Obesity and long term functional outcomes following elective total hip replacement

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Title:
Obesity and long term functional outcomes following elective total hip replacement
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English
Creator:
Vincent, Heather K.
Horodyski,, MaryBeth
Gearen, Peter
Vlasak, Richard
Seay, Amanda N.
Conrad, Bryan P.
Vincent, Kevin R.
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BioMed Central
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Abstract:
Introduction: Obesity rates continue to rise and more total hip arthroplasty procedures are being performed in progressively younger, obese patients. Hence, maintenance of long term physical function will become very important for quality of life, functional independence and hip prosthesis survival. Presently, there are no reviews of the long term efficacy of total hip arthroplasty on physical function. This review: 1) synopsized available data regarding obesity effects on long term functional outcomes after total hip arthroplasty, and 2) suggested future directions for research. Methods: A literature search was conducted from 1965 to January of 2011 for studies that evaluated long term functional outcomes at one year or longer after THA in obese (body mass index values ≥30 kg/m2) and non-obese patients (body mass index <30 kg/m2). Results: Five retrospective studies and 18 prospective studies were identified as those that assessed physical function before surgery out to ≥ one year after total hip arthroplasty. Study sample sizes ranged from 108–18,968 and followed patients from one to twenty years. Total hip arthroplasty confers significant pain reduction and improvement in quality of life irrespective of body mass index. Functional improvement occurred after total hip arthroplasty among all studies, but obese patients generally did not attain the same level of physical function by the follow-up time point. Discussion: Uncontrolled obesity after total hip arthroplasty is related to worsening of comorbidities and excessive health care costs over the long term. Aggressive and sustainable rehabilitation strategies that include physical exercise, psychosocial components and behavior modification may be highly useful in maximizing and maintaining weight loss after total hip arthroplasty. Keywords: Arthroplasty, Body mass index, Hip, Physical function, Disability, Obesity
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doi:10.1186/1749-799X-7-16 Cite this article as: Vincent et al.: Obesity and long term functional outcomes following elective total hip replacement. Journal of Orthopaedic Surgery and Research 2012 7:16.
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Vincent et al. Journal of Orthopaedic Surgery and Research 2012, 7:16 http://www.josr-online.com/content/7/1/16; Pgs. 1-12

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Vincent et al. Journal of Orthopaedic Surgery and Research 2012, 7:16
http://www.josr-online.com/content/7/1/16


Obesity and long term functional outcomes

following elective total hip replacement

Heather K Vincent, MaryBeth Horodyski, Peter Gearen, Richard Vlasak, Amanda N Seay,
Bryan P Conrad and Kevin R Vincent


Abstract
Introduction: Obesity rates continue to rise and more total hip arthroplasty procedures are being performed in
progressively younger, obese patients. Hence, maintenance of long term physical function will become very
important for quality of life, functional independence and hip prosthesis survival. Presently, there are no reviews of
the long term efficacy of total hip arthroplasty on physical function. This review: 1) synopsized available data
regarding obesity effects on long term functional outcomes after total hip arthroplasty, and 2) suggested future
directions for research.
Methods: A literature search was conducted from 1965 to January of 2011 for studies that evaluated long term
functional outcomes at one year or longer after THA in obese (body mass index values >30 kg/m2) and non-obese
patients (body mass index <30 kg/m2).
Results: Five retrospective studies and 18 prospective studies were identified as those that assessed physical
function before surgery out to > one year after total hip arthroplasty. Study sample sizes ranged from 108-18,968
and followed patients from one to twenty years. Total hip arthroplasty confers significant pain reduction and
improvement in quality of life irrespective of body mass index. Functional improvement occurred after total hip
arthroplasty among all studies, but obese patients generally did not attain the same level of physical function by
the follow-up time point.
Discussion: Uncontrolled obesity after total hip arthroplasty is related to worsening of comorbidities and excessive
health care costs over the long term. Aggressive and sustainable rehabilitation strategies that include physical
exercise, psychosocial components and behavior modification may be highly useful in maximizing and maintaining
weight loss after total hip arthroplasty.
Keywords: Arthroplasty, Body mass index, Hip, Physical function, Disability, Obesity


Introduction
The obese segment of the population with osteoarthritis is
burgeoning, and the demand for total hip arthroplasty
(THA) surgeries to treat obese persons is rising rapidly. Pri-
mary THA procedures will likely become necessary for a
greater prevalence of the U.S. population who is developing
debilitating OA earlier in life, and revision THAs will be-
come more frequent as these young adults age and the life
of the joint component ends. Evidence indicates that the
relative risk ratio for undergoing elective hip replacement

* Correspondence' vincehk@ortho ufl edu
interdisciplinary Center for Musculoskeletal Training and Research,
Department of Orthopaedics and Rehabilitation, Divisions of Research, Joint
Reconstruction, & Physical Medicine and Rehabilitation, University of Florida,
Gainesville, FL 32611, USA


ranges from 1.92 in overweight individuals to 8.56 in se-
verely obese individuals [1]. While extensive evidence has
focused on surgical outcomes, mortality medical complica-
tions after hip replacement [2], the relationship between
functional outcomes and obesity after THA over the long
term is not well understood, particularly in the obese pa-
tient. This is a significant scientific deficit as restoration of
physical function is one of the primary goals of THA [3,4].
As obesity rates continue rising and more THAs are
being performed in progressively younger, obese patients,
long term functional goals will become important. Func-
tional goals may include maintaining independence with
load bearing activities of daily living, independent mobility
and body transfers over the long term. Many obese patients


S2012 Vincent et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
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Vincent et al. Journal of Orthopaedic Surgery and Research 2012, 7:16
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with THA will be recommended to perform exercise (heavy
demand or weight bearing activity) for weight loss. In
addition, progressively more obese patients with THA % 11
be living longer with a joint implant and may be at risk for
failure and poorer quality of life over the long duration
compared with non-obese patients. For example, 35% of
patients with THA experience severe activity I -.( .-I.. by
year five; obesity .j,..::i. i..t predicted complete depend-
ence on :.i!! ,. aids and is associated with depression at
i1 ,...p1 [5]. The physical component of quality of life is
also lower in obese patients years after the procedure [6-8].
Hence, a clear understanding the effect of obesity on func-
tional outcomes after THA will be critical in establishing
expectations for the patients and care team and develop-
ment of strategies to optimize physical function and inde-
pendent mobility for as long as possible. Therefore, the
purposes of this review are to: 1) provide a current synopsis
of the available data i :..*:.:l-1. obesity effects on long term
functional outcomes after THA, and 2) to .,!,---i future
directions for research.

Search strategy
We conducted a literature search from 1965 to January
of 2011 in Medline, Cochrane Controlled Trials ". --I i.
CINAHL, Scopus and Web of Science. The search strat-
egy identified studies in English that examined the rela-
tionships between obesity or BMI, physical function after
total hip replacement. A functional measurement of mo-
bility, ambulation or transfers or a comprehensive self-
report tool that assesses physical function had to have
been reported a minimum of six months of !.II... -,,
after surgery. Estimates of obesity had to have been
reported including body mass index i-'.' ih body fat per-
centage or fat mass. Medical subject headings :'.I :. 1;/
keywords with all subheadings and as free text included
obesity, obese, mobility, functional limitation, physical
function, body fat, adiposity, waist circumference, total
hip replacement and hip arthroplasty. Studies that admi-
nistered surveys that reflected the perceived physical
functional ability were also included; these tools included
the Oxford Hip score (OHS), Harris Hip score Ir i -.
Western Ontario McMaster Osteoarthritis Index
(WOMAC) score or other specially constructed surveys
that included function-based questions, such as the Uni-
versity of California Los Angeles (UCLA) hip scoring
system. Studies that used functional tests !.' ill .... tests,
chair rise or timed up and go or body transfers or other
self care tasks) were also included. A total of 552 papers
were initially generated from this search. Studies that
had a i,..11 ,i' of less than six months, did not report
any form of functional measure at follow-up or did not
include an assessment of obesity were not included. The
lists of references of retrieved publications were manu-
ally checked to add any citations missed by the electronic


searches. Obesity was defined as an excessive body
weight >100 kg, a BMI >30 kg/m2 [9], or a large waist
circumference (>88 cm women, >102 cm men) [10].

Characteristics of included studies
A total of 23 articles were reviewed. Twenty articles
included self-report assessments of the WOMAC, HHS
or OHS or other survey based tools of physical function.
Eight studies included objective physical function assess-
ments. -.in. 1. were conducted in the United -. .i-
[7,11-13], Europe (: ; l. i: ,l,. [14], Scotland [15], the
United Kingdom [6,16-19], Switzerland [3], Denmark
_-ii,. Canada [2,21] and Australia [22-25]. Study sample
sizes ranged from 140 [15] to '',* [3] and were com-
prised of 17-77% women, .i. -.. '.in, on the study. We
identified three multicenter studies (two from Britain,
one from Switzerland, and one with 7 to 20 sites)
[3,16,18] and two studies based on joint surgery regis-
tries (American-based registry study) [13] and a Canad-
ian based registry [26].
Several studies demonstrated variability in the follow-up
time points for assessment, which limits generalizability of
the findings. For example, two retrospective studies cap-
tured follow up data from 0.1-15.6 years [14] and from
10-18.9 years [11]. Other retrospective studies captured
follow-up times out to one year [2] or at .l. -..- points of
time during the years i.,1,... .. the surgery [7,11,24]. A
few prospective studies contained t. II.... L data from dif-
ferent time points during years following the procedure
[23,27].

Hip surgical components and approaches
n; 'i. technique, component type and use of cement
varied among and within the identified studies. Several
surgical techniques were used across the studies, includ-
ing anterolateral [6,14,16,19], posterior [7,16,23], lateral
[28] and posterolateral [I1 -.'] approaches. There was
also variation in the type of component used, and ce-
ment use for fixation of the component. Cement proce-
dures were .., I-, -.. 1 in six studies [6,7,14,15,29,30], and
two studies described a mixed procedure of one cemen-
ted component and one non-cement component [28,31].
Numerous studies did not report or clearly describe the
components or the surgical procedure [2,3,13,15,17-
19,22,24,26,29,32]. Only a few of the studies ..-a..1.!!..:
the number of surgeons performing the arthroplasties,
thereby :.. ... .i some control over the variation in the
operating room procedures [17 i] Therefore, the
specific surgical iir, :. were widely varied among the
study pool.

Retrospective evidence
We identified five retrospective studies, and the sum-
maries of these studies are found in Table 1. Three


Page 2 of 12







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Table 1 Retrospective studies of functional outcomes in obese and non-obese patients with total hip arthroplasty
(THA)


Sample


193 to 1 year; Retrospective 61% were women BMI was
Mean age 63.5 years found for each patient


Haverkamp 411 Mean out to 20 years;
et al [14] (2008) Retrospective






LeDuff et al 770 210 years;
[7] (2007) Retrospective










McLaughlin 285 10-18 years;
& Lee [33] Retrospective





Yeung et a 2,026 6.3 year mean
[24] (2010) follow-u p; Retrospective


69% were women; BMI groups
were <25, > 25 and >30 kg/m2
Mean ages were 64-66 years
among groups



17% were women BMI groups
were < or > 30 kg/m2
Mean age 49 years









51% were women; BMI groups
were <30 or >30 kg/m Mean
ages 54-57 years



53% were female; BMI groups
were <30 or >30 kg/m2


Surgical Type & Components
Surgical components not
described; surgical type not
described: data obtained from
medical charts and .


Anterolateral approach;
Weber rotation THA System
(Allopro) with cement;





Posterior approach; 30-37%
of metaphyseal stem femora
components were cemented;
Conserve Plus hip resurfacing
prostheses were used







Uncemented T-tap acetabular
components (Biomet Inc.) and
Taperloc femoral points in obese
patients and from 53 to components
were used by one surgeon; al
were posterolateral approaches
Cementless procedures used;
components and approached were
not described


Study
Braeken
et al [2] (1997


THA = total hip arthroplasty; BMI = body mass index; EUROHIP = European Collaborative Database of Cost and Practice Patterns of Total Hip Replacement.
OR = odds ratio; RR = relative risk; HHS = Harris Hip Score; UCLA = University of California and Los Angeles (UCLA) activity scale; Medical Outcomes SF-12= Short
Form 12; WOMAC = Western Ontario and McMaster Osteoarthritis Index; VAS = visual analogue scale.
NS = not specified.


studies evaluated obesity effects on HHS score values
over varied :..-!..: .. time points out to 20 years. A
BMI value of >30 kg/m2 was related with a 4-9% lower
HHS scores at :,.II...' i. than BMI values less than
30 kg/m2 [14 i Despite HHS score .iI. ., .: .. im-
plant survival duration was similar by year 11. One
study that assessed follow-up HHS scores did not find
!il0, ; ... in improvement levels between non-obese
and obese patients after the procedure [11]. This corre-
sponded with no differences in revision rates or medical
complications. Two other reports showed that patients
with higher BMI values had 4-9% lower HHS scores at


maximum follow-up time of 1-10 years [14,24], and sig-
nificantly less range of motion during hip flexion, ad-
duction, internal rotation and lower knee flexion values
than patients with normal BMI values. Similar to the
findings of McLaughlin and Lee [11], Yeung et al [24]
reported no differences in the probability of 11 year in
implant survival based on BMI.
One study examined whether the functional and qual-
ity of life outcomes of hip resurfacing varied among non-
obese and obese patients using data obtained from an in-
stitutional ..-h; i. [7]. Data were obtained from clinical
visits at four months, one year and annually after


N Follow-up


Results
While high BMI was related
to high postoperative pain
levels, BMI itself was not a
strong contributor to the
regression model for
WOMAC functional score
(parameter estimate value
of 0.092).
HHS scores were progressively
lower for higher BMI brackets
at maximum follow-up time
(91.6, 86.8 and 83.7 points;
p 0.02); revision rates were
similar among BMI complication
rates and groups
By 6.2 years of follow-up, UCLA
scores for function and activity
werelower in the obese patients
than non-obese patients by -8%;
SF-12 physical component scores
were also lower in the obese
group (49.3 vs 51.4 points;
p 0.013); 5 year survivorship was
90.6% and 98.6% in patients with
BMI <25 and 30 kg/m2,
respectively.
By follow-up HHS 1 from 52 to
89 89 points in non-obese
patients, with no difference
between groups; no differences
in revision rates or complications
occurred between groups
HHS scores were lower for the
obese compared to the
non-obese patients at
follow-up (89.9 vs 93.2 points;
p < 0.001); HHS scores for
function, activities, hip range
of motion were lower in the
obese group (all p < 0.05);
survival rates were for the
implants were similar at year
11 (95-96%)


Page 3 of 12






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surgery, with -',!! ... -.-u times ranging from 2-10 years.
In obese patients, post-operative HHS score were 3.2
points lower, UCLA sub-scores for "function" and "activ-
ity" were 4-7% lower than those of the non-obese
patients. UCLA sub-scores of "-.. ::1! "'" were not differ-
ent between groups. Interestingly, survival of the hip im-
plant was higher in the obese patients compared to the
non-obese patients by year 5 (98.6% vs 90.6%).

Prospective evidence
Table 2 summarizes the prospective studies that we iden-
tified. Six studies used HHS as primary endpoints
.1 7,19,28], one study used OHS [16], one used the
UCLA activity score [31], and six studies employed the
WOMAC survey scores [8,18,26,28,34,35] as a main out-
come. Six studies used actual functional measures and
patient reported functional abilities .. i '.1~i .4 ,]

Harris hip score
HHS scores and functional sub-scores were captured at
a variety of time points ranging from one to five years.
In one study, sub-scores of HHS were reported in non-
obese and obese patients with THA by three years post-
surgery [15]. Sub-scores of % iii .11 distance, climbing
stairs, putting on shoes and socks, sitting and hip range
of motion were 4-25% lower in the obese group at fol-
low-up. Despite mean improvements in HHS and mobil-
ity, the cohort tended to gain weight by year three.
Another study tracked functional and clinical outcomes
in a group of morbidly obese patients with THA out to
year five; HHS scores improved significantly in all
patients by month six [6]. While the HHS scores were
higher in non-obese patients by year five, the absolute
improvement in scores were not i, i, based on obes-
ity status (52.0 vs 48.1 point change). Also, the morbidly
obese patients had more peri-operative complications
(12 vs 3 complications) and the five year survival was
9(0 .. and 100% in the obese and non-obese patients.
Both sex and revision status may be important factors
,..,1: .. ...^ HHS outcomes. For example, HHS scores
were evaluated among patients with a primary or revi-
sion THA in a Swiss cohort [28]. Patients with revisions
had a relative risk of 1.67 for being obese, and BMI was
found to be a stronger inverse predictor of HHS after re-
vision procedures than primary procedures by year five.
In a related study by the same author [8], HHS scores
were ..l, ..I in Swiss patients five years after THA
procedures and found that 81% and 70% of non-obese
and obese patients had good to excellent outcomes,
defined as a HHS score >80 points. These poorer out-
comes were i,. i, ..ii .1 in women than men. For example,
HHS scores in non-obese and obese women were 87.8
and 79.6 points respectively, and were 90.5 and 87.4
points in non-obese and obese men.


Among predictive and correlational studies, Moran et al
[19] examined whether BMI predicted HHS scores at fol-
low-up times of six and 18 months post-THA. While no
BMI-specific HHS data were presented, the authors
reported a small but significant multiple regression coeffi-
cient for BMI on the model for the follow-ups HHS. This
translated to a reduction in HHS by 0.25-0.35 points per
one point increase in BMI value. Another correlational
study that we included did not report actual HHS scores,
but superimposed HHS scores onto the Rosser Disability
Index matrix to generate a "quality of life" score as a
method of. .1m; i'., functional disability [17]. The find-
ings revealed that the median quality of life scores were
not different among patients with low and high BMI values
at one and three years of1 .' l'.' 'q- [17]. The authors con-
cluded that progressively higher BMI values up to 40 kg/
m2 were not related with these i I il, estimates.

WOMAC scores
One study examined the predictive value of one to four fac-
tors relating to the metabolic syndrome on WOMAC
scores before and at one year after THA [26]. These factors
included large waist circumference (>102 cm men, >88 cm
women), elevated triglycerides and low high density lipopro-
tein cholesterol, high blood pressure and elevated f' -r .:
blood glucose. BMI was calculated for each patient. P :-_: ..
sion analyses were performed to determine the effect of the
number of metabolic syndrome factors on WOMAC scores
by year one. The regression beta coefficient of having 4
metabolic factors on 1..-:l .r;.,i of WOMAC scores was
16.1 in this obese patient group compared with the beta co-
efficient of 0.6 in non-obese patients with one factor. The
coefficient for obesity alone was 2.4 (p = 0.03).
A study that analyzed data from twelve European
countries showed that one year WOMAC scores are
related to BMI [18]. Median baseline WOMAC scores
were higher in morbidly obese and obese patients com-
pared with non-obese patients (68.1 and 61.5 vs 57.6
points) but the median change in WOMAC scores was
l,;.1- i in the morbidly obese group by year one (56.1 vs
33.3 and 37.5 points; p = 0.012). In this cohort, the multi-
variate odds ratio of returning to normal functional sta-
tus was 3.1 compared to non-obese patients.
Lubbeke et al. performed two hospital-based cohorts
examining the 1) five year outcomes in obese men and
women with THA [8], and 2) the effects of ...I.!. i,..li.
and age after primary and revision THA [28]. In the first
study, sex differences in survey outcomes were analyzed in
a cohort of patients with THA. The crude incidence rate
was 4.7 times higher for infection, and the incidence rate
was 2.3 times higher for dislocation in obese patients com-
pared to non-obese patients. Five-year WOMAC function
sub-scores were 11% lower in obese women than men and
8% lower in non-obese women than men. Within each sex


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Table 2 Prospective studies of functional outcomes in obese and non-obese patients with total hip arthroplasty (THA)


Study N Follow-up

Aderinto et al [15] 140 3 years; Prospective
(2005) Follow-up


Andrew et al [16]
(2008)


1,421 5 years; Multi
center Prospective


Busato et al [3] 18,968 15 years; Multi-
(2008) center prospective






Chan and Villar [17] 166 to 3 years;
(1996) Prospective cohort





Chee et al [6] 108 5 years; Prospective
(2010) cohort







Dowsey et al [29] 471 1 year; Prospective
(2010) follow-up


Gandhi et al [26]
(2010)


707 hips I year
Prospective cohort


Jackson et al [23] 2,026 mean of 5 years;
(2009) Prospective cohort


Sample


61% were women;
groups were
<30 or >30 kg/m2






62% were women;
BMI groups were
<30, 30- <40 and
>40 kg/m2 Mean
ages were 69.1, 65.
and 60.6 years


sexes NS; BMI groups
were <25, 25- <30
and > 30 kg/m2





59% were women BMI
groups were <25,
25-29.9, 30-39.9,
>40 kg/m2 Mean ages
were 71.4, 69.0 and
68.1 years
41% were women; BM
groups were <35 kg/m2
or >35 (1 comorbidity)
and >40 kg/m2





60% were women; BM
groups were <30, 30-39
and > 40.0 kg/m2







59-66% were women;
waist circumference was
assessed for metabolic
syndrome BMI ranged
from 22.0 to 36.6 kg/m2
64.8-66.2 years


77% were women;
BMI groups were
Mean ages were 68
and 63 years


Surgical Type &
Components
Cemented prostheses;
approaches or components
were not described






Anterolateral or posterior
approaches were used;
cemented Stryker Exeter
femoral components and
several different acetabular
components




Surgical components not
described; surgical type not
described; Data were
obtained from the Total Hip
Registry (Switzerland)



Surgical components not
described; surgical type
not described




Anterolateral approach was
used on all patients; 25.5%
Charnley prosthesis
(dePuy, Int.), 74.5% Lubinus
SPII prosthesis (Waldmar-Link
GmbH); cemented



Surgical procedures not
described; surgical components
not described; cement used
varied across groups






Surgical components or
procedures not described;
patients were obtained
from a registry




Posterior surgical approach;
ABG2 Stryker cementless
femoral and acetabular
components


Results

At year 3, HHS scores 1 from 44 to
90 points (non-obese) and from
42.5 to 85 points (obese), with no
difference between groups; lower
scores for stairs, sitting and putting on
shoes-socks and range of motion
were lower in the obese patients
(p < 0.05).
By year 5, OHS scores were
best in the non-obese group
and worst in the obese group
(19.6 vs 25.6 points; p 0.005),
but no differences in the 5 year
change in OHS scores existed.
No differences in rates of revision,
dislocations or medical
complications existed.
High preoperative BMI was related
with a dose-effect response with
shorter unsupported walking
time less normal stair climb, and
shoe tying during the 15 year
follow-up, despitesimilar pain
relief across BMI brackets.
HHS scores were superimposed
onto the Rosser Index Matrix
(which ranks disability status); there
were no differences in Rosser scores
for disability among the BMI groups
by year 3.
Five year HHS were higher in
non-obese than morbidly obese
patients (91.8 vs 854 points;
p < 0.0001) despite similar pre-
operative scores; SF-36 subscores
for physical functioning were lower
in morbidly obese patients at
year 5.
Morbidly obese patients had a
lower change in HHS function
scores than obese and non-obese
patients, respectively by year
1(11.5 vs 15.6 and 16.2 points,
respectively); HHS were lowest
in morbidly obese patients by
year 1 (70.5 vs 79.8 and 80.8
points p 0.03).
1 year WOMAC scores (pain, function)
were highest in patients with 4
metabolic syndrome factors compared
to those with fewer factors; regression
B coefficients showed that obesity
predicted 1 year WOMAC scores
(B-2.4 1.4-4.2; 95% CI).
HHS were lower in obese vs
non-obese patients at follow-up
(89.9 vs 93.2 points); HHS functional
scores were also lower in the
obese group (29.6 vs 31.0 points);
hip flexion, adduction and internal
rotation ranges were less in the
obese vs non-obese patients. HHS
pain scores were not different
between groups.







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Table 2 Prospective studies of functional outcomes in obese and non-obese patients with total hip arthroplasty (THA)
(Continued)


1,327 1 year EUROHIP
Study of 20 orthopedic
centers


435 5-year; Prospective
cohort


Lubbeke et al [8] 2,495 5-year; Prospective
(2007) cohort


Lubbeke et al [30]
(2008)









Lubbeke et al [31]
(2010)


204 5-year; Prospective
cohort









503 5 or 10 years;
Prospective follow-up


Moran et al [19] 800 6-18 mo; Prospective
(2005) follow-up




Naylor et al [22] 198 1 year; Prospective
(2008) observational


56% were women;
BMI groups were <30,
30-39 and >40 kg/m2
Ages <50 to > 70 years


53-55% are women;
BMI groups were
30 kg/m2
Mean ages were
68 72 years


48.7-57.5% women;
8.5-9% were revisions;
BMI groups were < or > 30
kg/m2 Mean age 69 years


50-7.9% were women;
BMI groups were<
or 30 kg/m2 Age
range <50 to t80 years







58% were women; BM
groups were <25, 25-29.9
and > 30 kr/m2


61% women; BMI groups
were <25, 25-29.9,
30-39.9 >40 kg/m2 Mean
age was 68 years


56% were women; BM
groups were <30
or >30 kg/m2 Mean
age 67 years


Surgical components not
described; surgical type
not described


85% of patients had mixed
components
(1 cemented., non)


95% were lateral THA approach,
86% used Morscher press-fit
uncemented actetabular
component and Muller
straight stem cobalt chromium
femoral component


Cemented acetabular cups
were used in 67% and 80%
of obese and non-obese
patients







Hybrid prosthesis; Morscher
press fit uncemented cup and
cemented cobalt-chromium
stem (Zimmer); alumni
ceramic head, and a ceramic-
polyethylene surface


All were anterolatera
approach surgeries;
components were not
described


Surgical components not
described; approaches
not described


Judge et al [18]
(2010)


Median WOMAC scores were highest
in the morbidly obese group pre-THR,
(68.1 vs 61.5 and 57.6 points).

but the 1 year change in WOMAC
score was highest in the morbidly
obese group (median score change
of 56.1 vs 33.3 and 37.5 points);
morbidly obese patients showed
a 1 OR of "returning to normal"
(functionality) than the other groups.
Obesity was related with worse
outcomes after revision than primary
THA by year 5 (lower HHS scores: 76.7
vs 88.1 points; lower WOMAC function
scores 61.6 vs 70.0 points). BMI was
related to the mean difference of
HHS scores for primary and revision
THA (R coeffcient--1.0
[-0.1 to -1.95% CI]).
BMI of 30 kg/m2 was related with a
RR of 3.7-4.0 for revisions, 9.1-12.5 for
dislocations andl.9-8.0 for infections
in obese compared to non-obese
men and women. By year 5, HHS
were 87.8 and 79.6 points in non-
obese and obese women and 90.5
vs 87.4 points in non-obese and
obese men; WOMAC function
scores were 14.7% and 8.0% lower
in obese women and men thantheir
non-obese counterparts.

HHS were 82.8 14.7 and 71.4 17.0
points in the non-obese and obese
patients by year 5. Surgical revisions
were performed at 92 and 125 months
in obese and non-obese groups,
respectively. The adjusted hazard ratio
for occurrence of infection, dislocation
or re-revision increased from 1.0
(BMI < 25) to 1.5 (BMI 25-29.9) to
4.5 (BMI 30-34.9) to 10.9 (BMI >35.0).

At year 5, HHS j with each rogressively
higher BMI group (91.4, 88.4 and 85.1
points; p 0.019). At year 10, HHS
tended to be lower in patients with
BMI 30 kg/m2 compared with those
with BMI <25 and 25-29.9 kg/m2
(83.6 vs 87.3 and 87.1 points; p-0.08);
more obese patients had low UCLA
scores and more non-obese patients
had higher UCLA scores.

For every 1 point increase in BMI,
HHS scores dropped by 0.25 by
month 6 and by 0.35 by month
18 post-surgery. No BMI effect on
early failure of THA was found.

Obese patients had smaller increases
in timed mobility than non-obese
patients (0.23 m/s slower on 15 m
walk time) and the timed up and
go test (3.1 sec slower) at year 1;
WOMAC scores for function and
pain were worse in obese than
non-obese patients by year 1.


Lubbeke et al [28]
(2007)







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Page 7 of 12


Table 2 Prospective studies of functional outcomes in obese and non-obese patients with total hip arthroplasty (THA)
(Continued)


Singh et al [12] 2,687 2-5 years; Prospective
(2009) cohort of revision THA










Sballe et a (1987) 125 5 years;
[20] Prospective follow-up






Stickles et al [13] 5921 year; Prospective
(2001) follow-up


53-54% were women; BMI
brackets were <25,
25-29.9,30-39.9 >40 kg/m2
Mean 5 year age
was 65 years







A weight index was
calculated as < or > 120%
of pre-surgical weight;
analyses were also
performed using weight
brackets of< or> 80 kg;
Mean age at follow-up
70 (28-89) years
56% were women; BMI
brackets were <25,
25-29.9,30-40 >40 kg/m2
Mean age 69 years


Surgical components not
described; approaches
not described









All were posterolatera
approach surgeries;
Lubinus prostheses
were used and fixed with
gentamicin impregnated
radiopaque PMMA; One
surgeon performed all hip
replacements
Surgical components or
procedures not described;
patients were obtained
from a registry


At year 2, the OR for complete
dependence onwa king/gait aids
was 2.0 (vs 0.9 for BMI 25-29.9);
moderate to severe activity
imitation was predicted by
high BMI. The OR of reporting
difficulty in 3 of 7 mobility and
functional tasks T from 1.2 to 2.7
with increased BMI from 25-29.9
to 40 kg/m2, by year five, the OR
increased to 1.3 and 3.0 in these
same BMI brackets (all p<0.01).
Walking ability, defined using the
Charnley scoring system was lower
in patients with a weight index >120
pre-surgery, but similar to patients
with indexes <120 by year 5
(4.9 vs 5.0 points; p NSig).


By year 1, stair ascension and
descension difficulty was reported
in 86-88% of very obese patients
compared with 46-55% of
non-obese patients; BMI did not
correlate with change in WOMAC
scores (31.8 and 35.9 points, in
non-obese and very obese
patients, respectively; p > 0.05).


THA = total hip arthroplasty; BMI = body mass index; EUROHIP = European Collaborative Database of Cost and Practice Patterns of Total Hip Replacement.
OR = odds ratio; RR = relative risk; HHS = Harris Hip Score; UCLA = University of California and Los Angeles (UCLA) activity scale; Medical Outcomes SF-12 = Short
Form 12; WOMAC = Western Ontario and McMaster Osteoarthritis Index; VAS = visual analogue scale.
NSig = non-significant.


group, obese women and men had 8-11% lower WOMAC
function sub-scores than their non-obese counterparts. In
the second study, patients with primary and revision pro-
cedures were administered the WOMAC at five years [28].
of note, the patients with revisions were more often obese
than not. The WOMAC function sub-score was reported
to be lower in obese patients with revision THA compared
with non-obese patients (61.6 vs 70.0 points). This differ-
ence was deemed small but clinically significant.
A sample of Australian patients with primary unilateral
THA was analyzed for i. ..i- in WOMAC responses
by year one [34]. The obese patients reported improve-
ments in WOMAC function subscores from 44.6 to 23.3
points while the non-obese patients demonstrated
improvements in this same subscore from 40.7 to 13.7
points. Hence, the non-obese patients showed a greater
relative functional improvement than obese patients at
year one. Stickles et al [35] prospectively assessed
WOMAC responses in persons with THA across the BMI
spectrum: <25, 25-20, 30-35, 35-40 and >40 kg/m2. At
one year after surgery, WOMAC scores were progressively
less with each higher BMI bracket. There were no differ-
ences among BMI brackets in the total complication rate,
medical I"...':.. .... rate or orthopedic complication
rate.


Oxford hip scores (OHS)
One study presented responses to the Oxford Hip survey
in groups with low and high BMIs. Andrew et al. [16].
compared the OHS in non-obese, obese and morbidly
obese patients pre-surgery, three months and annually
until year five. By year three, the average OHS was high-
est in the non-obese group and lowest in the morbidly
obese group (19.6 + 8.6 vs 23.5 + 11.4 points); this pattern
was maintained out to year five. However, the five year
change in absolute OHS was not :. i.v. ..1 based on BMI,
o.-... i.-* comparable responsiveness to the procedure
over the long term. There were no differences in the
rates of perisurgical medical complications or long term
femoral stem position, femoral osteolysis or implant
survival.

UCLA activity score
A prospective study that compared the osteolysis rates
and patient satisfaction after THA was conducted by
Lubbeke et al [31]. The patient activity level was assessed
using the UCLA survey at the pre-surgery time point
and at years five and ten after THA. Patients were strati-
fied into non-obese, overweight, and obese groups based
on BMI. While the mean UCLA scores were similar be-
tween groups at follow-up, the 6.8% of obese patients






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.11. !..-- ..I- .... ./content/7/1/16


achieved a high activity UCLA score compared to 11.7%
overweight and 14.4% of normal weight groups. This
finding was corroborated with lower follow-up HHS in
the obese group compared to the remaining groups.
Obese patients had poorer pain scores and an odds ratio
of 1.44 of developing femoral osteolysis whereas the nor-
mal weight had an odds ratio of 2.64 compared to the
reference overweight group.

Functional tests
Several studies assessed functional capacity with walking
tests, stair climbing, and timed functional tests. In an
early study, I. J: -*',; ability was a primary functional five
year endpoint for a Danish cohort of patients with THA
[20]. Radiographic and surgical outcomes were measured
in addition to -.il : ability. The Charnley criteria [36]
were applied to -. ii .1 i ability (6 points= walking, no
limp; 5 points = extensive -. :.i .'-. with or without cane,
with limp; 4 points= moderate ,.. ii' ... with one crutch
or cane; 3 points =restricted walking with crutches; 2
points= wheelchair transfer activity; 1 point= bedridden)
before and after THA. Patients were -*( :.rtr..: i based on a
weight index (< or >120% of normal weight for height
and sex) or by body weight (<80 kg or >80 kg). Pre-op-
eratively, :ii 1^; ability scores were .1 .1.. .- based on
% of normal weight (1.8 vs 2.3 points in heavy versus
non-heavy patients, respectively; p < 0.05) but not abso-
lute body weight (2.2 points for both groups). Five years
post-THA, Charnely walking scores were not iill ....
based on either expression of body size. While surgical
blood loss was greater in heavy patients compared with
non-heavy patients, there were no ,_,,r .1. differences
in operation time, medical complications or loosening of
the implant based on weight.
Naylor et al [34] in Australia, performed short functional
tests in obese and non-obese patients before and at various
time points out to year one. These tests included a 15-
meter walking test and a timed-up-and-go (TUG) test
where an individual rises from a chair and returns to the
chair. While obesity did not preclude improvement in 15
meter -. ii .._. speed, the trajectory of change was lower in
the obese group by year one, and final walking speeds were
1.37 m/s and 1.14 m/s in non-obese and obese -i .r re-
spectively. Similarly, improvements in TUG test time were
slower in the obese group by year one (final TUG times
were 9.2 sec and 12.4 sec in the non-obese and obese
patients). The approximate 30% an 42% improvements in
walk and TUG times were not different based on obesity
status. There was a 2.8% greater chance that obese patients
would use a .- .1: ., aid at follow-up compared to non-
obese counterparts.
Difficulty ascending and .:1. .. .-_-:1;I- stairs was one end-
point in a prospective study of American patients hip or
knee arthroplasty [35]. Among the patients with THA, and


it was shown that the percentage of patients in each pro-
gressively higher BMI bracket (<25 to >40 kg/m [2])
reported ,i.iT.. ,lh with descending and ascending stairs.
This functional pattern was corroborated with self-report
WOMAC data, which showed lower scores in the one year
total WOMAC score and related physical component sub-
score in severely obese patients compared to non-obese
patients. Total ,! .. .i: complication rate was not i ::. 1i,1
across the BMI spectrum. However, a major limitation to
the study was that the i.- -`. technique used to capture
this stair climbing information was not presented in the
methods.
In a cohort of American patients with revision THA, ac-
tivity limitation and dependence on -.. :)1 !!I. aids was
assessed by Singh et al [12] at years two and five post-
THA. The evidence revealed that the odds ratio of devel-
oping moderate-severe physical activity limitation
increased from 1.2 to 2.7 in overweight and morbidly obese
patients. Severe obesity increased the two and five year
odds ratios of developing complete dependence on walking
aids to 2.0 and 2.7 compared with the reference of normal
weight.
Busato et al [3] collected a series of functional measure-
ments in a cohort of Swiss patients with THA at periodic
',1,... i: including ll 11 distance without support,
hip flexion range, stair climbing and putting on shoes and
socks. Data were reported as the percent of patients who
were able to achieve :1' .. >60 minutes, hip flexion
range >90 and capacity for normal stair climb and don-
ning of footwear. Irrespective of time point, fewer obese
patients were able to walk >60 minutes without support
and this percentage continued to lowered 27.2% from year
three to year 12 compared with the 18.5% fewer non-obese
patients. This same pattern occurred with stair climbing
and with tying shoes by year 12. Interestingly, the obese
patients increased the hip flexion range of motion by 7.8%,
whereas the non-obese group lost 11.6% of hip flexion mo-
tion by year 12. In all three BMI strata, pain relief was
achieved in the majority of patients and was largely main-
tained by year 12.
Hip range of motion was assessed in non-obese and
obese patients with cementless THA at a median follow-
up time of 5.1 years in addition to pain ratings, survey
scores and implant survival. Despite equivalent implant
survival rates between groups, obese patients achieved
9.4 less range of movement about the hip than non-
obese patients with flexion, 2 less adduction and 2.8 less
of internal rotation. Interestingly, pain relief and patient
satisfaction with the procedure were similar between
groups at follow-up.

Overview of the findings
Of the evidence included in this review, the surgical
component, cementation or surgical approach did not


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appear to have any consistent effect on long term func-
tional outcomes in the obese patient. Of the 23 studies,
16 reported that obesity was associated with lower hip
function survey scores at follow-up, whereas four studies
did not. Five studies revealed negative long term effects
of obesity on various tasks of physical function, and one
study noted no adverse influence of obesity on walking
ability. While obesity does not necessarily preclude func-
tional improvements after surgery, the functional gains
achieved and the self-reported functional ability ...-- .II
are lower than those attained by non-obese patients.
Thus, evidence indicates that there is significant pain re-
lief and patient satisfaction after THA in obese patients,
whereas these patients fall short of achieving the same
long term functional level as their non-obese counter-
parts. Hence, in a time frame of as short as one year after
THA, obese patients are already at a functional deficit
compared to non-obese counterparts.

Potential explanations for functional outcomes in the obese
patient
Some postulated mechanisms underlying this F."..l,"L in-
clude fear of movement and fear avoidance of physical
activities, poor skeletal muscle quality, elevated perceived
effort with physical tasks, and maintenance of pre-surgi-
cal physical activity patterns. Our research laboratory has
recently shown that obese patients fear pain induced by
physical activity and movement, and this corresponds to
lower self-reported physical abilities with tasks related to
mobility (e.g., -. :,!! .. stair ..i1, "-.; :. body transfers and
recreational activities that involve running, start and stop
motions and jumping) [37,38]. Despite a paucity of lit-
erature addressing the interactions of pain, obesity and
joint function over the long term, obese patients can
achieve high satisfaction and pain relief and still not in-
crease participation in physical activities at home and in
the community. Whether this is due to residual fear of
movement and avoidance of activities that may trigger
pain is unknown.
Muscle strength rather than muscle mass may be a
more in.. .11; relevant determinant of functional status
in the older population [39] ... ip.. tissue itself contri-
butes to muscle loss through chronic, low grade produc-
tion of inflammatory cytokines, adipokines and free fatty
acids [40]. These chemicals slowly erode muscle mass in
the older obese adult, unfavorably shifting the ratio of
muscle mass to fat mass. In addition, existing muscles
become infiltrated by fat [41], thereby lowering muscle
quality and functional ability of the muscle tissue. Re-
sidual post-operative strength deficits and fat infiltration
may occur in the hip flexors (.: -... :1:. i, .i- i i. I .
compared to non-repaired hip) out to two years [42];
these deficits may contribute to lower functional ability
with tasks that activate these muscles. Hence, independent


from the improvements in pain and quality of life after a
total hip replacement, the obese patient may not achieve
the same level of function as non-obese patient in part due
to skeletal muscle .1p, ,i ,, especially if the patient does not
change physical activity patterns to activate loading bearing
muscle groups after THA.
The level of perceived .l.ii,. 11 and effort with physical
activity is a critical issue for obese individuals, especially
those with BMI >40 kg/m2. Morbidly obese patients have
poor cardiac, metabolic and ventilatory efficiency and have
lower compensatory hyperventilation with exercise [43]. A
given exercise workload may require a lot of energy to
move heavier limb segments against :i i0. in the mor-
bidly obese individuals (manifested as lower mechanical ef-
ficiency) [44,45]. Self-reported fatigue is higher with
increasing BMI [46]. Mobility related tasks, such as short
and long distance timed-. ,il ..i:. tests, stair climb. TUG
tests are consistently more challenging and take longer to
perform with increasing BMI [47]. Musculoskeletal pain
may occur at high intensity activities and may be the limit-
ing factor and not true muscle iai .'. I .i ( ..i. It I
the higher perception of muscular effort and discomfort of
dyspnea may discourage this population from regularly en-
gaging in physical activities.
While quantitative evidence of physical activity patterns
after THA in obese adults is sparse, Donovan et al [48].
reported that patient perceptions of physical activity
improved by one year after surgery. A total of 43% and 9%
of the patients felt that their activity level improved "a lot
more" and "a little more" since prior to joint replacement,
respectively. The majority of the referenced ...~..: how-
ever, showed that weight gain or maintenance 1;:. ii.
occurs after THA, inferring that physical activity levels
were not dramatically altered from pre-surgical levels. It
has been postulated that with the resolution of hip pain
and decreased need for analgesics, normal appetites and
caloric intake returned and counteracted any potential ef-
fect of increased physical activity in the obese patient [49].

Does weight loss after THA improve long term functional
outcomes?
The assumption that THA would reduce hip pain, and
therefore foster increased physical activity and weight
loss in the obese patient is not presently substantiated by
the limited evidence. In fact, several studies report main-
tenance of current weight [48] or continued weight gain
(ranging from 2.5%-3.6% increase in BMI) one to two
years after THA [49-51]. Data suggest that >75% of
patients experience weight gain over three years [15].
This trend occurs in men and women, irrespective of
pre-surgical BMI [50]. However, in one prospective
study, the average weight gain by one year was 2.8 kg,
with the change occurring primarily in women [52]. In
another study, non-obese and obese patients did not lose


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weight, while overweight patients gained a significant
amount of weight after surgery [53]. P,. ,1 BMI
values at : ..... '.. were independent of improvement in
mobility using WOMAC score [51] or self-reported
improvements in mobility [54]. We surmise that the ma-
jority of patients undergoing primary THA will increase
their BMI given sufficient follow-up time, irrespective of
the outcome [51]. Further investigation of strategies that
can be used to encourage perioperative weight loss and
slow, safe weight loss after surgery will be important for
functional change and preservation of the joint pros-
thesis i; : III

Clinical implications
Obese patients with THA are less functional than non-
obese counterparts. If over time the obese patient fails to
modify lifestyle, sarcopenic obesity worsens as a spiral of
deconditioning and functional dependence develops. The
ability to generate muscle strength and power will de-
cline without participation in physical activity. As the
obese patient ages and the negative lifestyle behaviors re-
main, obesity-related comorbidities will worsen. Add-
itional joint pains will develop and the joint implant will
ultimately fail earlier in life. Uncontrolled obesity after
THA will result in costly and complicated surgical revi-
sion procedures. This is a serious issue, because the
number of THA performed earlier in obese patients is
growing rapidly in the U.S. Possible solutions to this
combat this problem include: 1) a strong emphasis on
aggressive rehabilitation after THA that focuses on long
term maintenance of skeletal muscle quality and mass,
and 2) consistent, safe monitored weight loss over the
months T. !! .. .-.; the surgery to facilitate physical func-
tion and longevity of the joint implant.

Limitations to the evidence
There are several limitations that deserve comment.
TH .1 the determination of "physical function" varied
widely across the studies. In this population, there is not
yet a standard test battery performed before and after
surgery. Second, the reviewed studies ',1'... .I, did not
report severity or frequency of other musculoskeletal
pain that might be affected by THA. This issue is im-
portant, as the hip joint lies centrally to the lower body
cinematic chain. Correction of hip pain may improve
gait, posture and ambulation, thereby reducing other
joint symptoms in the spine and knee. We assume that
correction of pain and disability in the hip is the mech-
anism underlying functional improvement, particularly
in obese patients, but we are neglecting to address
whether THA has wider reaching effects on overall joint
mechanics and pain symptoms.
A substantial attrition rate occurred in many studies.
Attrition creates selection bias of the population, and in


many studies it was not clear how missing data were
handled. In some cases, only completers were included
in the analysis. Interpretation of long term results is con-
founded by the .I. .i......1 of selection bias. The lack of
emphasis on clinical importance has led to misconcep-
tions and I1 ..-.- :.-.. about the interpretation of the
results of clinical trials and a tendency to equate statis-
tical I i::.. .!!.. with clinical importance. In some
instances, statistically significant results may not be clin-
ically important and, conversely, statistically insignificant
results do not completely rule out the possibility of clin-
ically important effects [55].


Future directions
The National Health and Nutrition Examination Survey
III data show that lower body functional impairment is
becoming more prevalent in obese individuals; among
obese persons, 36.8% reported .:.-:.!i.r; in 1994, whereas
42.2% reported disability and functional impairment in
2004 [56]. Development of a battery of functional tests
of hip flexibility, muscle testing and mobility should be
standard practice for THA research to help predict func-
tional success of the surgery. A comprehensive pain and
fear assessment will help determine how systemic pain
relates to the symptoms and changes in the hip joint.
Prospective biomechanical assessments of lower body
kinematics in the surgical and non-surgical limb would
be very useful in tracking the long term joint motion and
physical capabilities. Psychiatric [57], psychosocial [58]
and behavioral traits [59] or genetic phenotypes [60]
associated with severe obesity should be factors to track
in future outcomes studies. There is a dire need for iden-
tification of specific exercise, psychosocial, pain manage-
ment and nutritional interventions that effectively
enhance gains made in physical function over the long
term. Finally, it would be clinically important to deter-
mine what amount of weight loss maximizes implant
lifespan.


Conclusions
THA confers significant pain reduction and improvement
in p, :1i.; of life irrespective of BMI. While functional im-
provement occurs after THA, available evidence indicates
that obese patients are less likely to attain the same level of
physical function over the long term. L -.. f...II, .: obesity
is related to worsening of comorbidities and excessive
health care costs over the long term. Aggressive and sus-
tainable rehabilitation strategies that include physical exer-
cise, psychosocial components and behavior modification
may be highly useful in maximizing and maintaining
weight loss after THA. Furthermore, this type of rehabili-
tation may also reduce the overall health care burden.


Page 10 of 12








Vincent et al. Journal of Orthopaedic Surgery and Research 2012, 7:16
.1s. !.-- .I- -... ./content/7/1/16


competing interests


Authors' contributions
HV primary writer MBH text contributor, editing PI
editing RV text contributor, ediLing ANS collection
contributor BPC text contributor, editing KRV text
authors read and approved the final manuscript


G text contributor,
of scientiec papers, text
:ontributor, editing A;1


Acknowledgements
This work has been supported by the University of Forda's interdisciplinary
Center for Muscuioskeietal Training and Research, Department of
Orthopaedi(cs and Rehab~iiialhon

Received: 9 March 2011 Accepted: 2 April 2012
Published: 25 April 2012


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Competing interests
She authors declare that tpev ha3


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doi:10.1186/1749-799X-7-16
Cite this article as: Vincent et al Obesity and long term functional
outcomes following elective total hip replacement. Journal of
Orthopaedic Surgery and Research 2012 7'16


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!DOCTYPE art SYSTEM 'http:www.biomedcentral.comxmlarticle.dtd'
ui 1749-799X-7-16
ji 1749-799X
fm
dochead Review
bibl
title
p Obesity and long term functional outcomes following elective total hip replacement
aug
au id A1 ca yes snm Vincentmi Kfnm Heatherinsr iid I1 email vincehk@ortho.ufl.edu
A2 HorodyskiMaryBethhorodmb@ortho.ufl.edu
A3 GearenPetergearepf@ortho.ufl.edu
A4 VlasakRichardvlasarg@ortho.ufl.edu
A5 SeayNAmandastevean@ortho.ufl.edu
A6 ConradPBryanconrapb@ortho.ufl.edu
A7 VincentRKevinvincekr@ortho.ufl.edu
insg
ins Interdisciplinary Center for Musculoskeletal Training and Research, Department of Orthopaedics and Rehabilitation, Divisions of Research, Joint Reconstruction, & Physical Medicine and Rehabilitation, University of Florida, Gainesville, FL, 32611, USA
source Journal of Orthopaedic Surgery and Research
issn 1749-799X
pubdate 2012
volume 7
issue 1
fpage 16
url http://www.josr-online.com/content/7/1/16
xrefbib pubidlist pubid idtype doi 10.1186/1749-799X-7-16pmpid 22533938
history rec date day 9month 3year 2011acc 242012pub 2542012
cpyrt 2012collab Vincent et al; licensee BioMed Central Ltd.note This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
kwdg
kwd Arthroplasty
Body mass index
Hip
Physical function
Disability
Obesity
abs
sec
st
Abstract
Introduction
Obesity rates continue to rise and more total hip arthroplasty procedures are being performed in progressively younger, obese patients. Hence, maintenance of long term physical function will become very important for quality of life, functional independence and hip prosthesis survival. Presently, there are no reviews of the long term efficacy of total hip arthroplasty on physical function. This review: 1) synopsized available data regarding obesity effects on long term functional outcomes after total hip arthroplasty, and 2) suggested future directions for research.
Methods
A literature search was conducted from 1965 to January of 2011 for studies that evaluated long term functional outcomes at one year or longer after THA in obese (body mass index values ≥30 kg/msup 2) and non-obese patients (body mass index <30 kg/m2).
Results
Five retrospective studies and 18 prospective studies were identified as those that assessed physical function before surgery out to ≥ one year after total hip arthroplasty. Study sample sizes ranged from 108–18,968 and followed patients from one to twenty years. Total hip arthroplasty confers significant pain reduction and improvement in quality of life irrespective of body mass index. Functional improvement occurred after total hip arthroplasty among all studies, but obese patients generally did not attain the same level of physical function by the follow-up time point.
Discussion
Uncontrolled obesity after total hip arthroplasty is related to worsening of comorbidities and excessive health care costs over the long term. Aggressive and sustainable rehabilitation strategies that include physical exercise, psychosocial components and behavior modification may be highly useful in maximizing and maintaining weight loss after total hip arthroplasty.
meta
classifications
classification subtype Primary type springerjournalsubject Musculoskeletal disorders
Secondary Sports medicine
Surgery
bdy
Introduction
The obese segment of the population with osteoarthritis is burgeoning, and the demand for total hip arthroplasty (THA) surgeries to treat obese persons is rising rapidly. Primary THA procedures will likely become necessary for a greater prevalence of the U.S. population who is developing debilitating OA earlier in life, and revision THAs will become more frequent as these young adults age and the life of the joint component ends. Evidence indicates that the relative risk ratio for undergoing elective hip replacement ranges from 1.92 in overweight individuals to 8.56 in severely obese individuals abbrgrp
abbr bid B1 1
. While extensive evidence has focused on surgical outcomes, mortality medical complications after hip replacement
B2 2
, the relationship between functional outcomes and obesity after THA over the long term is not well understood, particularly in the obese patient. This is a significant scientific deficit as restoration of physical function is one of the primary goals of THA
B3 3
B4 4
.As obesity rates continue rising and more THAs are being performed in progressively younger, obese patients, long term functional goals will become important. Functional goals may include maintaining independence with load bearing activities of daily living, independent mobility and body transfers over the long term. Many obese patients with THA will be recommended to perform exercise (heavy demand or weight bearing activity) for weight loss. In addition, progressively more obese patients with THA will be living longer with a joint implant and may be at risk for failure and poorer quality of life over the long duration compared with non-obese patients. For example, 35% of patients with THA experience severe activity limitation by year five; obesity significantly predicted complete dependence on walking aids and is associated with depression at follow-up
B5 5
. The physical component of quality of life is also lower in obese patients years after the procedure
B6 6
B7 7
B8 8
. Hence, a clear understanding the effect of obesity on functional outcomes after THA will be critical in establishing expectations for the patients and care team and development of strategies to optimize physical function and independent mobility for as long as possible. Therefore, the purposes of this review are to: 1) provide a current synopsis of the available data regarding obesity effects on long term functional outcomes after THA, and 2) to suggest future directions for research.
Search strategy
We conducted a literature search from 1965 to January of 2011 in Medline, Cochrane Controlled Trials Register, CINAHL, Scopus and Web of Science. The search strategy identified studies in English that examined the relationships between obesity or BMI, physical function after total hip replacement. A functional measurement of mobility, ambulation or transfers or a comprehensive self-report tool that assesses physical function had to have been reported a minimum of six months of follow-up after surgery. Estimates of obesity had to have been reported including body mass index (BMI), body fat percentage or fat mass. Medical subject headings (MeSH)/keywords with all subheadings and as free text included obesity, obese, mobility, functional limitation, physical function, body fat, adiposity, waist circumference, total hip replacement and hip arthroplasty. Studies that administered surveys that reflected the perceived physical functional ability were also included; these tools included the Oxford Hip score (OHS), Harris Hip score (HHS), Western Ontario McMaster Osteoarthritis Index (WOMAC) score or other specially constructed surveys that included function-based questions, such as the University of California Los Angeles (UCLA) hip scoring system. Studies that used functional tests (walking tests, chair rise or timed up and go or body transfers or other self care tasks) were also included. A total of 552 papers were initially generated from this search. Studies that had a follow-up of less than six months, did not report any form of functional measure at follow-up or did not include an assessment of obesity were not included. The lists of references of retrieved publications were manually checked to add any citations missed by the electronic searches. Obesity was defined as an excessive body weight >100 kg, a BMI ≥30 kg/m2
B9 9
, or a large waist circumference (>88 cm women, >102 cm men)
B10 10
.
Characteristics of included studies
A total of 23 articles were reviewed. Twenty articles included self-report assessments of the WOMAC, HHS or OHS or other survey based tools of physical function. Eight studies included objective physical function assessments. Studies were conducted in the United States
7
B11 11
B12 12
B13 13
, Europe (Netherlands
B14 14
, Scotland
B15 15
, the United Kingdom
6
B16 16
B17 17
B18 18
B19 19
, Switzerland
3
, Denmark
B20 20
), Canada
2
B21 21
and Australia
B22 22
B23 23
B24 24
B25 25
. Study sample sizes ranged from 140
15
to 18,968
3
and were comprised of 17-77% women, depending on the study. We identified three multicenter studies (two from Britain, one from Switzerland, and one with 7 to 20 sites)
3
16
18
and two studies based on joint surgery registries (American-based registry study)
13
and a Canadian based registry
B26 26
.Several studies demonstrated variability in the follow-up time points for assessment, which limits generalizability of the findings. For example, two retrospective studies captured follow up data from 0.1-15.6 years
14
and from 10–18.9 years
11
. Other retrospective studies captured follow-up times out to one year
2
or at different points of time during the years following the surgery
7
11
24
. A few prospective studies contained follow-up data from different time points during years following the procedure
23
B27 27
.
Hip surgical components and approaches
Surgical technique, component type and use of cement varied among and within the identified studies. Several surgical techniques were used across the studies, including anterolateral
6
14
16
19
, posterior
7
16
23
, lateral
B28 28
and posterolateral
11
20
approaches. There was also variation in the type of component used, and cement use for fixation of the component. Cement procedures were described in six studies
6
7
14
15
B29 29
B30 30
, and two studies described a mixed procedure of one cemented component and one non-cement component
28
B31 31
. Numerous studies did not report or clearly describe the components or the surgical procedure
2
3
13
15
17
18
19
22
24
26
29
B32 32
. Only a few of the studies controlled the number of surgeons performing the arthroplasties, thereby providing some control over the variation in the operating room procedures
17
23
24
. Therefore, the specific surgical details were widely varied among the study pool.
Retrospective evidence
We identified five retrospective studies, and the summaries of these studies are found in Table tblr tid T1 1. Three studies evaluated obesity effects on HHS score values over varied follow-up time points out to 20 years. A BMI value of >30 kg/m2 was related with a 4-9% lower HHS scores at follow-up than BMI values less than 30 kg/m2
14
24
. Despite HHS score differences, implant survival duration was similar by year 11. One study that assessed follow-up HHS scores did not find differences in improvement levels between non-obese and obese patients after the procedure
11
. This corresponded with no differences in revision rates or medical complications. Two other reports showed that patients with higher BMI values had 4-9% lower HHS scores at maximum follow-up time of 1–10 years
14
24
, and significantly less range of motion during hip flexion, adduction, internal rotation and lower knee flexion values than patients with normal BMI values. Similar to the findings of McLaughlin and Lee
11
, Yeung et al
24
reported no differences in the probability of 11 year in implant survival based on BMI.
table
Table 1
caption
b Retrospective studies of functional outcomes in obese and non-obese patients with total hip arthroplasty (THA)
tgroup align left cols 5
colspec colname c1 colnum 1 colwidth 1*
c2 2
c3 3
c4 4
c5
thead valign top
row rowsep
entry
Study
N Follow-up
Sample
Surgical Type & Components
Results
tfoot
THA = total hip arthroplasty; BMI = body mass index; EUROHIP = European Collaborative Database of Cost and Practice Patterns of Total Hip Replacement.OR = odds ratio; RR = relative risk; HHS = Harris Hip Score; UCLA = University of California and Los Angeles (UCLA) activity scale; Medical Outcomes SF-12 = Short Form 12; WOMAC = Western Ontario and McMaster Osteoarthritis Index; VAS = visual analogue scale.NS = not specified.
tbody
Braeken et al
2
(1997)
193 to 1 year; Retrospective Mean age 63.5 years
61% were women BMI was found for each patient
Surgical components not described; surgical type not described: data obtained from medical charts and mailings
While high BMI was related to high postoperative pain levels, BMI itself was not a strong contributor to the regression model for WOMAC functional score (parameter estimate value of 0.092).
Haverkamp et al
14
(2008)
411 Mean out to 20 years; Retrospective
69% were women; BMI groups were <25, ≥ 25 and >30 kg/m2 Mean ages were 64–66 years among groups
Anterolateral approach; Weber rotation THA System (Allopro) with cement;
HHS scores were progressively lower for higher BMI brackets at maximum follow-up time (91.6, 86.8 and 83.7 points; p = 0.02); revision rates were similar among BMI complication rates and groups
LeDuff et al
7
(2007)
770 2–10 years; Retrospective
17% were women BMI groups were < or ≥ 30 kg/m2 Mean age 49 years
Posterior approach; 30-37% of metaphyseal stem femoral components were cemented; Conserve Plus hip resurfacing prostheses were used
By 6.2 years of follow-up, UCLA scores for function and activity werelower in the obese patients than non-obese patients by ~8%; SF-12 physical component scores were also lower in the obese group (49.3 vs 51.4 points; p = 0.013); 5 year survivorship was 90.6% and 98.6% in patients with BMI <25 and 30 kg/m2, respectively.
McLaughlin & Lee
B33 33
285 10–18 years; Retrospective
51% were women; BMI groups were <30 or ≥30 kg/m2 Mean ages 54–57 years
Uncemented T-tap acetabular components (Biomet Inc.) and Taperloc femoral points in obese patients and from 53 to components were used by one surgeon; all were posterolateral approaches
By follow-up HHS ↑ from 52 to 89 89 points in non-obese patients, with no difference between groups; no differences in revision rates or complications occurred between groups
Yeung et al
24
(2010)
2,026 6.3 year mean follow-up; Retrospective
53% were female; BMI groups were <30 or ≥30 kg/m2
Cementless procedures used; components and approached were not described
HHS scores were lower for the obese compared to the non-obese patients at follow-up (89.9 vs 93.2 points; p < 0.001); HHS scores for function, activities, hip range of motion were lower in the obese group (all p < 0.05); survival rates were for the implants were similar at year 11 (95-96%)
One study examined whether the functional and quality of life outcomes of hip resurfacing varied among non-obese and obese patients using data obtained from an institutional registry
7
. Data were obtained from clinical visits at four months, one year and annually after surgery, with follow-up times ranging from 2–10 years. In obese patients, post-operative HHS score were 3.2 points lower, UCLA sub-scores for “function” and “activity” were 4-7% lower than those of the non-obese patients. UCLA sub-scores of “walking” were not different between groups. Interestingly, survival of the hip implant was higher in the obese patients compared to the non-obese patients by year 5 (98.6% vs 90.6%).
Prospective evidence
Table T2 2 summarizes the prospective studies that we identified. Six studies used HHS as primary endpoints
6
8
15
17
19
28
, one study used OHS
16
, one used the UCLA activity score
31
, and six studies employed the WOMAC survey scores
8
18
26
28
B34 34
B35 35
as a main outcome. Six studies used actual functional measures and patient reported functional abilities
3
12
20
23
34
35
.
Table 2
Prospective studies of functional outcomes in obese and non-obese patients with total hip arthroplasty (THA)
Study
N Follow-up
Sample
Surgical Type & Components
Results
THA = total hip arthroplasty; BMI = body mass index; EUROHIP = European Collaborative Database of Cost and Practice Patterns of Total Hip Replacement.OR = odds ratio; RR = relative risk; HHS = Harris Hip Score; UCLA = University of California and Los Angeles (UCLA) activity scale; Medical Outcomes SF-12 = Short Form 12; WOMAC = Western Ontario and McMaster Osteoarthritis Index; VAS = visual analogue scale.NSig = non-significant.
Aderinto et al
15
(2005)
140 3 years; Prospective Follow-up
61% were women; groups were <30 or ≥30 kg/m2
Cemented prostheses; approaches or components were not described
At year 3, HHS scores ↑ from 44 to 90 points (non-obese) and from 42.5 to 85 points (obese), with no difference between groups; lower scores for stairs, sitting and putting on shoes-socks and range of motion were lower in the obese patients (p < 0.05).
Andrew et al
16
(2008)
1,421 5 years; Multi- center Prospective
62% were women; BMI groups were <30, 30- < 40 and ≥40 kg/m2 Mean ages were 69.1, 65.5 and 60.6 years
Anterolateral or posterior approaches were used; cemented Stryker Exeter femoral components and several different acetabular components
By year 5, OHS scores were best in the non-obese group and worst in the obese group (19.6 vs 25.6 points; p = 0.005), but no differences in the 5 year change in OHS scores existed. No differences in rates of revision, dislocations or medical complications existed.
Busato et al
3
(2008)
18,968 15 years; Multi- center prospective
sexes NS; BMI groups were <25, 25- <30 and ≥ 30 kg/m2
Surgical components not described; surgical type not described; Data were obtained from the Total Hip Registry (Switzerland)
High preoperative BMI was related with a dose-effect response with shorter unsupported walking time less normal stair climb, and shoe tying during the 15 year follow-up, despitesimilar pain relief across BMI brackets.
Chan and Villar
17
(1996)
166 to 3 years; Prospective cohort
59% were women BMI groups were <25, 25–29.9, 30–39.9, >40 kg/m2 Mean ages were 71.4, 69.0 and 68.1 years
Surgical components not described; surgical type not described
HHS scores were superimposed onto the Rosser Index Matrix (which ranks disability status); there were no differences in Rosser scores for disability among the BMI groups by year 3.
Chee et al
6
(2010)
108 5 years; Prospective cohort
41% were women; BMI groups were <35 kg/m2 or >35 (1 comorbidity) and >40 kg/m2
Anterolateral approach was used on all patients; 25.5% Charnley prosthesis (dePuy, Int.), 74.5% Lubinus SPII prosthesis (Waldmar-Link GmbH); cemented
Five year HHS were higher in non-obese than morbidly obese patients (91.8 vs 85.4 points; p < 0.0001) despite similar pre- operative scores; SF-36 subscores for physical functioning were lower in morbidly obese patients at year 5.
Dowsey et al
29
(2010)
471 1 year; Prospective follow-up
60% were women; BMI groups were <30, 30–39 and ≥ 40.0 kg/m2
Surgical procedures not described; surgical components not described; cement used varied across groups
Morbidly obese patients had a lower change in HHS function scores than obese and non-obese patients, respectively by year 1(11.5 vs 15.6 and 16.2 points, respectively); HHS were lowest in morbidly obese patients by year 1 (70.5 vs 79.8 and 80.8 points p = 0.03).
Gandhi et al
26
(2010)
707 hips I year Prospective cohort
59-66% were women; waist circumference was assessed for metabolic syndrome BMI ranged from 22.0 to 36.6 kg/m2 64.8-66.2 years
Surgical components or procedures not described; patients were obtained from a registry
1 year WOMAC scores (pain, function) were highest in patients with 4 metabolic syndrome factors compared to those with fewer factors; regression B coefficients showed that obesity predicted 1 year WOMAC scores (B = 2.4 1.4-4.2; 95% CI).
Jackson et al
23
(2009)
2,026 mean of 5 years; Prospective cohort
77% were women; BMI groups were Mean ages were 68 and 63 years
Posterior surgical approach; ABG2 Stryker cementless femoral and acetabular components
HHS were lower in obese vs non-obese patients at follow-up (89.9 vs 93.2 points); HHS functional scores were also lower in the obese group (29.6 vs 31.0 points); hip flexion, adduction and internal rotation ranges were less in the obese vs non-obese patients. HHS pain scores were not different between groups.
Judge et al
18
(2010)
1,327 1 year EUROHIP Study of 20 orthopedic centers
56% were women; BMI groups were <30, 30–39 and ≥40 kg/m2 Ages <50 to ≥ 70 years
Surgical components not described; surgical type not described
Median WOMAC scores were highest in the morbidly obese group pre-THR, (68.1 vs 61.5 and 57.6 points). but the 1 year change in WOMAC score was highest in the morbidly obese group (median score change of 56.1 vs 33.3 and 37.5 points); morbidly obese patients showed a ↑ OR of “returning to normal” (functionality) than the other groups.
Lubbeke et al
28
(2007)
435 5-year; Prospective cohort
53-55% are women; BMI groups were  < or ≥ 30 kg/m2 Mean ages were 68 72 years
85% of patients had mixed components (1 cemented,1 non)
Obesity was related with worse outcomes after revision than primary THA by year 5 (lower HHS scores: 76.7 vs 88.1 points; lower WOMAC function scores 61.6 vs 70.0 points). BMI was related to the mean difference of HHS scores for primary and revision THA (R coefficient = −1.0 [−0.1 to −1.95% CI]).
Lubbeke et al
8
(2007)
2,495 5-year; Prospective cohort
48.7-57.5% women; 8.5-9% were revisions; BMI groups were < or ≥ 30  kg/m2 Mean age 69 years
95% were lateral THA approach, 86% used Morscher press-fit uncemented actetabular component and Muller straight stem cobalt chromium femoral component
BMI of ≥30 kg/m2 was related with a RR of 3.7-4.0 for revisions, 9.1-12.5 for dislocations and1.9-8.0 for infections in obese compared to non-obese men and women. By year 5, HHS were 87.8 and 79.6 points in non- obese and obese women and 90.5 vs 87.4 points in non-obese and obese men; WOMAC function scores were 14.7% and 8.0% lower in obese women and men thantheir non-obese counterparts.
Lubbeke et al
30
(2008)
204 5-year; Prospective cohort
50-7.9% were women; BMI groups were <  or ≥ 30 kg/m2 Age range <50 to ≥80 years
Cemented acetabular cups were used in 67% and 80% of obese and non-obese patients
HHS were 82.8 ± 14.7 and 71.4 ± 17.0 points in the non-obese and obese patients by year 5. Surgical revisions were performed at 92 and 125 months in obese and non-obese groups, respectively. The adjusted hazard ratio for occurrence of infection, dislocation or re-revision increased from 1.0 (BMI < 25) to 1.5 (BMI 25–29.9) to 4.5 (BMI 30–34.9) to 10.9 (BMI ≥35.0).
Lubbeke et al
31
(2010)
503 5 or 10 years; Prospective follow-up
58% were women; BMI groups were <25, 25–29.9 and ≥ 30 kg/m2
Hybrid prosthesis; Morscher press fit uncemented cup and cemented cobalt-chromium stem (Zimmer); alumnia ceramic head, and a ceramic- polyethylene surface
At year 5, HHS ↓ with each rogressively higher BMI group (91.4, 88.4 and 85.1 points; p = 0.019). At year 10, HHS tended to be lower in patients with BMI ≥30 kg/m2 compared with those with BMI <25 and 25–29.9 kg/m2 (83.6 vs 87.3 and 87.1 points; p = 0.08); more obese patients had low UCLA scores and more non-obese patients had higher UCLA scores.
Moran et al
19
(2005)
800 6–18 mo; Prospective follow-up
61% women; BMI groups were <25, 25–29.9, 30–39.9 ≥40 kg/m2 Mean age was 68 years
All were anterolateral approach surgeries; components were not described
For every 1 point increase in BMI, HHS scores dropped by 0.25 by month 6 and by 0.35 by month 18 post-surgery. No BMI effect on early failure of THA was found.
Naylor et al
22
(2008)
198 1 year; Prospective observational
56% were women; BMI groups were <30 or ≥30 kg/m2 Mean age 67 years
Surgical components not described; approaches not described
Obese patients had smaller increases in timed mobility than non-obese patients (0.23 m/s slower on 15 m walk time) and the timed up and go test (3.1 sec slower) at year 1; WOMAC scores for function and pain were worse in obese than non-obese patients by year 1.
Singh et al
12
(2009)
2,687 2–5 years; Prospective cohort of revision THA
53-54% were women; BMI brackets were <25, 25–29.9, 30–39.9 ≥40 kg/m2 Mean 5 year age was 65 years
Surgical components not described; approaches not described
At year 2, the OR for complete dependence onwalking/gait aids was 2.0 (vs 0.9 for BMI 25–29.9); moderate to severe activity limitation was predicted by high BMI. The OR of reporting difficulty in 3 of 7 mobility and functional tasks ↑ from 1.2 to 2.7 with increased BMI from 25–29.9 to 40 kg/m2, by year five, the OR increased to 1.3 and 3.0 in these same BMI brackets (all p < 0.01).
Søballe et al (1987)
20
125 5 years; Prospective follow-up
A weight index was calculated as < or > 120% of pre-surgical weight; analyses were also performed using weight brackets of < or > 80 kg; Mean age at follow-up 70 (28–89) years
All were posterolateral approach surgeries; Lubinus prostheses were used and fixed with gentamicin impregnated radiopaque PMMA; One surgeon performed all hip replacements
Walking ability, defined using the Charnley scoring system was lower in patients with a weight index >120 pre-surgery, but similar to patients with indexes <120 by year 5 (4.9 vs 5.0 points; p = NSig).
Stickles et al
13
(2001)
5921 year; Prospective follow-up
56% were women; BMI brackets were <25, 25–29.9, 30–40 >40 kg/m2 Mean age 69 years
Surgical components or procedures not described; patients were obtained from a registry
By year 1, stair ascension and descension difficulty was reported in 86-88% of very obese patients compared with 46-55% of non-obese patients; BMI did not correlate with change in WOMAC scores (31.8 and 35.9 points, in non-obese and very obese patients, respectively; p > 0.05).
Harris hip score
HHS scores and functional sub-scores were captured at a variety of time points ranging from one to five years. In one study, sub-scores of HHS were reported in non-obese and obese patients with THA by three years post-surgery
15
. Sub-scores of walking distance, climbing stairs, putting on shoes and socks, sitting and hip range of motion were 4-25% lower in the obese group at follow-up. Despite mean improvements in HHS and mobility, the cohort tended to gain weight by year three. Another study tracked functional and clinical outcomes in a group of morbidly obese patients with THA out to year five; HHS scores improved significantly in all patients by month six
6
. While the HHS scores were higher in non-obese patients by year five, the absolute improvement in scores were not different based on obesity status (52.0 vs 48.1 point change). Also, the morbidly obese patients had more peri-operative complications (12 vs 3 complications) and the five year survival was 90.9% and 100% in the obese and non-obese patients.Both sex and revision status may be important factors influencing HHS outcomes. For example, HHS scores were evaluated among patients with a primary or revision THA in a Swiss cohort
28
. Patients with revisions had a relative risk of 1.67 for being obese, and BMI was found to be a stronger inverse predictor of HHS after revision procedures than primary procedures by year five. In a related study by the same author
8
, HHS scores were collected in Swiss patients five years after THA procedures and found that 81% and 70% of non-obese and obese patients had good to excellent outcomes, defined as a HHS score ≥80 points. These poorer outcomes were magnified in women than men. For example, HHS scores in non-obese and obese women were 87.8 and 79.6 points respectively, and were 90.5 and 87.4 points in non-obese and obese men.Among predictive and correlational studies, Moran et al
19
examined whether BMI predicted HHS scores at follow-up times of six and 18 months post-THA. While no BMI-specific HHS data were presented, the authors reported a small but significant multiple regression coefficient for BMI on the model for the follow-ups HHS. This translated to a reduction in HHS by 0.25-0.35 points per one point increase in BMI value. Another correlational study that we included did not report actual HHS scores, but superimposed HHS scores onto the Rosser Disability Index matrix to generate a “quality of life” score as a method of estimating functional disability
17
. The findings revealed that the median quality of life scores were not different among patients with low and high BMI values at one and three years of follow-up
17
. The authors concluded that progressively higher BMI values up to 40 kg/m2 were not related with these disability estimates.
WOMAC scores
One study examined the predictive value of one to four factors relating to the metabolic syndrome on WOMAC scores before and at one year after THA
26
. These factors included large waist circumference (>102 cm men, >88 cm women), elevated triglycerides and low high density lipoprotein cholesterol, high blood pressure and elevated fasting blood glucose. BMI was calculated for each patient. Regression analyses were performed to determine the effect of the number of metabolic syndrome factors on WOMAC scores by year one. The regression beta coefficient of having 4 metabolic factors on prediction of WOMAC scores was 16.1 in this obese patient group compared with the beta coefficient of 0.6 in non-obese patients with one factor. The coefficient for obesity alone was 2.4 (p = 0.03).A study that analyzed data from twelve European countries showed that one year WOMAC scores are related to BMI
18
. Median baseline WOMAC scores were higher in morbidly obese and obese patients compared with non-obese patients (68.1 and 61.5 vs 57.6 points) but the median change in WOMAC scores was highest in the morbidly obese group by year one (56.1 vs 33.3 and 37.5 points; p = 0.012). In this cohort, the multivariate odds ratio of returning to normal functional status was 3.1 compared to non-obese patients.Lubbeke et al. performed two hospital-based cohorts examining the 1) five year outcomes in obese men and women with THA
8
, and 2) the effects of comorbidities and age after primary and revision THA
28
. In the first study, sex differences in survey outcomes were analyzed in a cohort of patients with THA. The crude incidence rate was 4.7 times higher for infection, and the incidence rate was 2.3 times higher for dislocation in obese patients compared to non-obese patients. Five-year WOMAC function sub-scores were 11% lower in obese women than men and 8% lower in non-obese women than men. Within each sex group, obese women and men had 8-11% lower WOMAC function sub-scores than their non-obese counterparts. In the second study, patients with primary and revision procedures were administered the WOMAC at five years
28
. of note, the patients with revisions were more often obese than not. The WOMAC function sub-score was reported to be lower in obese patients with revision THA compared with non-obese patients (61.6 vs 70.0 points). This difference was deemed small but clinically significant.A sample of Australian patients with primary unilateral THA was analyzed for differences in WOMAC responses by year one
34
. The obese patients reported improvements in WOMAC function subscores from 44.6 to 23.3 points while the non-obese patients demonstrated improvements in this same subscore from 40.7 to 13.7 points. Hence, the non-obese patients showed a greater relative functional improvement than obese patients at year one. Stickles et al
35
prospectively assessed WOMAC responses in persons with THA across the BMI spectrum: <25, 25–20, 30–35, 35–40 and >40 kg/m2. At one year after surgery, WOMAC scores were progressively less with each higher BMI bracket. There were no differences among BMI brackets in the total complication rate, medical complication rate or orthopedic complication rate.
Oxford hip scores (OHS)
One study presented responses to the Oxford Hip survey in groups with low and high BMIs. Andrew et al.
16
. compared the OHS in non-obese, obese and morbidly obese patients pre-surgery, three months and annually until year five. By year three, the average OHS was highest in the non-obese group and lowest in the morbidly obese group (19.6 ± 8.6 vs 23.5 ± 11.4 points); this pattern was maintained out to year five. However, the five year change in absolute OHS was not different based on BMI, indicating comparable responsiveness to the procedure over the long term. There were no differences in the rates of perisurgical medical complications or long term femoral stem position, femoral osteolysis or implant survival.
UCLA activity score
A prospective study that compared the osteolysis rates and patient satisfaction after THA was conducted by Lubbeke et al
31
. The patient activity level was assessed using the UCLA survey at the pre-surgery time point and at years five and ten after THA. Patients were stratified into non-obese, overweight, and obese groups based on BMI. While the mean UCLA scores were similar between groups at follow-up, the 6.8% of obese patients achieved a high activity UCLA score compared to 11.7% overweight and 14.4% of normal weight groups. This finding was corroborated with lower follow-up HHS in the obese group compared to the remaining groups. Obese patients had poorer pain scores and an odds ratio of 1.44 of developing femoral osteolysis whereas the normal weight had an odds ratio of 2.64 compared to the reference overweight group.
Functional tests
Several studies assessed functional capacity with walking tests, stair climbing, and timed functional tests. In an early study, walking ability was a primary functional five year endpoint for a Danish cohort of patients with THA
20
. Radiographic and surgical outcomes were measured in addition to walking ability. The Charnley criteria
B36 36
were applied to walking ability (6 points = walking, no limp; 5 points = extensive walking, with or without cane, with limp; 4 points = moderate walking with one crutch or cane; 3 points = restricted walking with crutches; 2 points = wheelchair transfer activity; 1 point = bedridden) before and after THA. Patients were stratified based on a weight index (< or >120% of normal weight for height and sex) or by body weight (<80 kg or >80 kg). Pre-operatively, walking ability scores were different based on % of normal weight (1.8 vs 2.3 points in heavy versus non-heavy patients, respectively; p < 0.05) but not absolute body weight (2.2 points for both groups). Five years post-THA, Charnely walking scores were not different based on either expression of body size. While surgical blood loss was greater in heavy patients compared with non-heavy patients, there were no significant differences in operation time, medical complications or loosening of the implant based on weight.Naylor et al
34
in Australia, performed short functional tests in obese and non-obese patients before and at various time points out to year one. These tests included a 15-meter walking test and a timed-up-and-go (TUG) test where an individual rises from a chair and returns to the chair. While obesity did not preclude improvement in 15 meter walking speed, the trajectory of change was lower in the obese group by year one, and final walking speeds were 1.37 m/s and 1.14 m/s in non-obese and obese patients, respectively. Similarly, improvements in TUG test time were slower in the obese group by year one (final TUG times were 9.2 sec and 12.4 sec in the non-obese and obese patients). The approximate 30% an 42% improvements in walk and TUG times were not different based on obesity status. There was a 2.8% greater chance that obese patients would use a walking aid at follow-up compared to non-obese counterparts.Difficulty ascending and descending stairs was one endpoint in a prospective study of American patients hip or knee arthroplasty
35
. Among the patients with THA, and it was shown that the percentage of patients in each progressively higher BMI bracket (<25 to >40 kg/m
2
) reported difficulty with descending and ascending stairs. This functional pattern was corroborated with self-report WOMAC data, which showed lower scores in the one year total WOMAC score and related physical component subscore in severely obese patients compared to non-obese patients. Total medical complication rate was not different across the BMI spectrum. However, a major limitation to the study was that the specific technique used to capture this stair climbing information was not presented in the methods.In a cohort of American patients with revision THA, activity limitation and dependence on walking aids was assessed by Singh et al
12
at years two and five post-THA. The evidence revealed that the odds ratio of developing moderate-severe physical activity limitation increased from 1.2 to 2.7 in overweight and morbidly obese patients. Severe obesity increased the two and five year odds ratios of developing complete dependence on walking aids to 2.0 and 2.7 compared with the reference of normal weight.Busato et al
3
collected a series of functional measurements in a cohort of Swiss patients with THA at periodic follow-ups, including walking distance without support, hip flexion range, stair climbing and putting on shoes and socks. Data were reported as the percent of patients who were able to achieve walking >60 minutes, hip flexion range >90 and capacity for normal stair climb and donning of footwear. Irrespective of time point, fewer obese patients were able to walk >60 minutes without support and this percentage continued to lowered 27.2% from year three to year 12 compared with the 18.5% fewer non-obese patients. This same pattern occurred with stair climbing and with tying shoes by year 12. Interestingly, the obese patients increased the hip flexion range of motion by 7.8%, whereas the non-obese group lost 11.6% of hip flexion motion by year 12. In all three BMI strata, pain relief was achieved in the majority of patients and was largely maintained by year 12.Hip range of motion was assessed in non-obese and obese patients with cementless THA at a median follow-up time of 5.1 years in addition to pain ratings, survey scores and implant survival. Despite equivalent implant survival rates between groups, obese patients achieved 9.4 less range of movement about the hip than non-obese patients with flexion, 2 less adduction and 2.8 less of internal rotation. Interestingly, pain relief and patient satisfaction with the procedure were similar between groups at follow-up.
Overview of the findings
Of the evidence included in this review, the surgical component, cementation or surgical approach did not appear to have any consistent effect on long term functional outcomes in the obese patient. Of the 23 studies, 16 reported that obesity was associated with lower hip function survey scores at follow-up, whereas four studies did not. Five studies revealed negative long term effects of obesity on various tasks of physical function, and one study noted no adverse influence of obesity on walking ability. While obesity does not necessarily preclude functional improvements after surgery, the functional gains achieved and the self-reported functional ability generally are lower than those attained by non-obese patients. Thus, evidence indicates that there is significant pain relief and patient satisfaction after THA in obese patients, whereas these patients fall short of achieving the same long term functional level as their non-obese counterparts. Hence, in a time frame of as short as one year after THA, obese patients are already at a functional deficit compared to non-obese counterparts.
Potential explanations for functional outcomes in the obese patient
Some postulated mechanisms underlying this finding include fear of movement and fear avoidance of physical activities, poor skeletal muscle quality, elevated perceived effort with physical tasks, and maintenance of pre-surgical physical activity patterns. Our research laboratory has recently shown that obese patients fear pain induced by physical activity and movement, and this corresponds to lower self-reported physical abilities with tasks related to mobility (e.g., walking, stair climbing, body transfers and recreational activities that involve running, start and stop motions and jumping)
B37 37
B38 38
. Despite a paucity of literature addressing the interactions of pain, obesity and joint function over the long term, obese patients can achieve high satisfaction and pain relief and still not increase participation in physical activities at home and in the community. Whether this is due to residual fear of movement and avoidance of activities that may trigger pain is unknown.Muscle strength rather than muscle mass may be a more clinically relevant determinant of functional status in the older population
B39 39
. Adipose tissue itself contributes to muscle loss through chronic, low grade production of inflammatory cytokines, adipokines and free fatty acids
B40 40
. These chemicals slowly erode muscle mass in the older obese adult, unfavorably shifting the ratio of muscle mass to fat mass. In addition, existing muscles become infiltrated by fat
B41 41
, thereby lowering muscle quality and functional ability of the muscle tissue. Residual post-operative strength deficits and fat infiltration may occur in the hip flexors (15% strength difference compared to non-repaired hip) out to two years
B42 42
; these deficits may contribute to lower functional ability with tasks that activate these muscles. Hence, independent from the improvements in pain and quality of life after a total hip replacement, the obese patient may not achieve the same level of function as non-obese patient in part due to skeletal muscle quality, especially if the patient does not change physical activity patterns to activate loading bearing muscle groups after THA.The level of perceived difficulty and effort with physical activity is a critical issue for obese individuals, especially those with BMI ≥ 40 kg/m2. Morbidly obese patients have poor cardiac, metabolic and ventilatory efficiency and have lower compensatory hyperventilation with exercise
B43 43
. A given exercise workload may require a lot of energy to move heavier limb segments against gravity in the morbidly obese individuals (manifested as lower mechanical efficiency)
B44 44
B45 45
. Self-reported fatigue is higher with increasing BMI
B46 46
. Mobility related tasks, such as short and long distance timed walking tests, stair climb. TUG tests are consistently more challenging and take longer to perform with increasing BMI
B47 47
. Musculoskeletal pain may occur at high intensity activities and may be the limiting factor and not true muscle fatigue
45
. Collectively, the higher perception of muscular effort and discomfort of dyspnea may discourage this population from regularly engaging in physical activities.While quantitative evidence of physical activity patterns after THA in obese adults is sparse, Donovan et al
B48 48
. reported that patient perceptions of physical activity improved by one year after surgery. A total of 43% and 9% of the patients felt that their activity level improved “a lot more” and “a little more” since prior to joint replacement, respectively. The majority of the referenced studies, however, showed that weight gain or maintenance typically occurs after THA, inferring that physical activity levels were not dramatically altered from pre-surgical levels. It has been postulated that with the resolution of hip pain and decreased need for analgesics, normal appetites and caloric intake returned and counteracted any potential effect of increased physical activity in the obese patient
B49 49
.
Does weight loss after THA improve long term functional outcomes?
The assumption that THA would reduce hip pain, and therefore foster increased physical activity and weight loss in the obese patient is not presently substantiated by the limited evidence. In fact, several studies report maintenance of current weight
48
or continued weight gain (ranging from 2.5%-3.6% increase in BMI) one to two years after THA
49
B50 50
B51 51
. Data suggest that ≥75% of patients experience weight gain over three years
15
. This trend occurs in men and women, irrespective of pre-surgical BMI
50
. However, in one prospective study, the average weight gain by one year was 2.8 kg, with the change occurring primarily in women
B52 52
. In another study, non-obese and obese patients did not lose weight, while overweight patients gained a significant amount of weight after surgery
B53 53
. Post-surgical BMI values at follow-up were independent of improvement in mobility using WOMAC score
51
or self-reported improvements in mobility
B54 54
. We surmise that the majority of patients undergoing primary THA will increase their BMI given sufficient follow-up time, irrespective of the outcome
51
. Further investigation of strategies that can be used to encourage perioperative weight loss and slow, safe weight loss after surgery will be important for functional change and preservation of the joint prosthesis lifespan.
Clinical implications
Obese patients with THA are less functional than non-obese counterparts. If over time the obese patient fails to modify lifestyle, sarcopenic obesity worsens as a spiral of deconditioning and functional dependence develops. The ability to generate muscle strength and power will decline without participation in physical activity. As the obese patient ages and the negative lifestyle behaviors remain, obesity-related comorbidities will worsen. Additional joint pains will develop and the joint implant will ultimately fail earlier in life. Uncontrolled obesity after THA will result in costly and complicated surgical revision procedures. This is a serious issue, because the number of THA performed earlier in obese patients is growing rapidly in the U.S. Possible solutions to this combat this problem include: 1) a strong emphasis on aggressive rehabilitation after THA that focuses on long term maintenance of skeletal muscle quality and mass, and 2) consistent, safe monitored weight loss over the months following the surgery to facilitate physical function and longevity of the joint implant.
Limitations to the evidence
There are several limitations that deserve comment. First, the determination of “physical function” varied widely across the studies. In this population, there is not yet a standard test battery performed before and after surgery. Second, the reviewed studies typically did not report severity or frequency of other musculoskeletal pain that might be affected by THA. This issue is important, as the hip joint lies centrally to the lower body kinematic chain. Correction of hip pain may improve gait, posture and ambulation, thereby reducing other joint symptoms in the spine and knee. We assume that correction of pain and disability in the hip is the mechanism underlying functional improvement, particularly in obese patients, but we are neglecting to address whether THA has wider reaching effects on overall joint mechanics and pain symptoms.A substantial attrition rate occurred in many studies. Attrition creates selection bias of the population, and in many studies it was not clear how missing data were handled. In some cases, only completers were included in the analysis. Interpretation of long term results is confounded by the likelihood of selection bias. The lack of emphasis on clinical importance has led to misconceptions and disagreements about the interpretation of the results of clinical trials and a tendency to equate statistical significance with clinical importance. In some instances, statistically significant results may not be clinically important and, conversely, statistically insignificant results do not completely rule out the possibility of clinically important effects
B55 55
.
Future directions
The National Health and Nutrition Examination Survey III data show that lower body functional impairment is becoming more prevalent in obese individuals; among obese persons, 36.8% reported disability in 1994, whereas 42.2% reported disability and functional impairment in 2004
B56 56
. Development of a battery of functional tests of hip flexibility, muscle testing and mobility should be standard practice for THA research to help predict functional success of the surgery. A comprehensive pain and fear assessment will help determine how systemic pain relates to the symptoms and changes in the hip joint. Prospective biomechanical assessments of lower body kinematics in the surgical and non-surgical limb would be very useful in tracking the long term joint motion and physical capabilities. Psychiatric
B57 57
, psychosocial
B58 58
and behavioral traits
B59 59
or genetic phenotypes
B60 60
associated with severe obesity should be factors to track in future outcomes studies. There is a dire need for identification of specific exercise, psychosocial, pain management and nutritional interventions that effectively enhance gains made in physical function over the long term. Finally, it would be clinically important to determine what amount of weight loss maximizes implant lifespan.
Conclusions
THA confers significant pain reduction and improvement in quality of life irrespective of BMI. While functional improvement occurs after THA, available evidence indicates that obese patients are less likely to attain the same level of physical function over the long term. Uncontrolled obesity is related to worsening of comorbidities and excessive health care costs over the long term. Aggressive and sustainable rehabilitation strategies that include physical exercise, psychosocial components and behavior modification may be highly useful in maximizing and maintaining weight loss after THA. Furthermore, this type of rehabilitation may also reduce the overall health care burden.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
HV primary writer. MBH text contributor, editing. PFG text contributor, editing. RV text contributor, editing. ANS collection of scientific papers, text contributor. BPC text contributor, editing. KRV text contributor, editing. All authors read and approved the final manuscript.
bm
ack
Acknowledgements
This work has been supported by the University of Florida’s Interdisciplinary Center for Musculoskeletal Training and Research, Department of Orthopaedics and Rehabilitation.
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Surg200878643944410.1111/j.1445-2197.2008.04554.x18522562Metabolic syndrome and the functional outcomes of hip and knee arthroplastyGandhiRRazakFDaveyJRMahomedNNJ Rheumatol20103791917192210.3899/jrheum.09124220634242Results of surgical repair of abductor avulsion after primary total hip arthroplastyLübbekeAKampfenSSternRHoffmeyerPJ Arthroplast200823569469810.1016/j.arth.2007.08.018Primary and revision hip arthroplasty: 5-year outcomes and influence of age and comorbidityLübbekeAKatzJNPernegerTVHoffmeyerPJ Rheumatol200734239440017143967The impact of obesity on weight change and outcomes at 12 months in patients undergoing total hip arthroplastyDowseyMMLiewDStoneyJDChoongPFMedical Journal of Austria201019311721Outcomes of obese and nonobese patients undergoing revision total hip arthroplastyLübbekeAMoonsKGGaravagliaGHoffmeyerPArthritis and Rheumatism200859573874510.1002/art.2356218438918Influence of obesity on femoral osteolysis five and ten years following total hip arthroplastyLübbekeAGaravagliaGBareaCRoussosCSternRHoffmeyerPJournal of Bone and Joint Surgery American Volume201092101964197210.2106/JBJS.I.00749Effect of sex and living arrangement on the timing and outcome of joint replacement surgeryGandhiRRazakFDaveyJRRampersaudYRMahomedNNCan J Surg20105313741pmcid 281001920100411The outcome of total hip replacement in obese and non-obese patients at 10- to 18-yearsMcLaughlinJRLeeKRJournal of Bone and Joint Surgery, British volume200688101286129210.1302/0301-620X.88B10.17660Severe other joint disease and obesity independently influence recovery after joint replacement surgery: an observational studyNaylorJMHarmerARHeardRCAustralian Journal of Physiotherapy2008541576410.1016/S0004-9514(08)70067-918298360Defining the relationship between obesity and total joint arthroplastySticklesBPhillipsLBroxWTOwensBLanzerWLObesity R20019321922310.1038/oby.2001.24The long-term results of low-friction arthroplasty of the hip performed as a primary interventionCharnelyJJournal of Bone and Joint Surgery British Volume19725416176Morbid obesity is associated with fear of movement and lower quality of life in patients with knee pain-related diagnosesVincentHKLambKMDayTITillmanSMVincentKRGeorgeSZPM&R201028713722346082323029467Fear of movement, quality of life and self-reported disability in obese patients with chronic lumbar painVincentHKOmliMRDayTIHodgesMVincentKRGeorgeSZPain Med2011In press.Sarcopenic obesity: definition, cause and consequencesStenholmSHarrisTBRantanenTVisserMKritchevskySBFerrucciLCurrent Opinions in Clinical Nutrition and Metabolism Care200811669370010.1097/MCO.0b013e328312c37dObesity in older adults: relationship to functional limitationJensenGHsiaoPYCurrent Opinion in Clinical Nutrition and Metabolic Care2010131465110.1097/MCO.0b013e32833309cf19841579Skeletal muscle lipid concentration quantified by magnetic resonance imagingGoodpasterBHStengerVABoadaFetal Am J Clin Nutr200479574875415113711Muscle strength, gait, and balance in 20 patients with hip osteoarthritis followed for 2 years after THARaschADalénNBergHEActa Orthopedics201081218318810.3109/17453671003793204Poor compensatory hyperventilation in morbidly obese women at peak exerciseZavorskyGSMuriasJMKim doJGowJChristouNVRespiration, Physiologya nd Neurobiology200715918719510.1016/j.resp.2007.07.001Ventilatory and perceptual responses to cycle exercise in obese womenOfirDLavenezianaPWebbKAO’DonnellDEJ Appl Physiol20071022217222610.1152/japplphysiol.00898.200617234804Exercise capacity in lean versus obese womenHulensMVansantGLysensRClaessensALMulsEScandinavian Journal of Medicine and Sport Science200111530530910.1034/j.1600-0838.2001.110509.xShort-term changes of fatigability and muscle performance in severe obese patients after an integrated body mass reduction programSartorioAFontanaPTrecateLLafortunaCLDiabetes Nutrition and Metabolism20031628893Obesity and mobility disability in the older adultVincentHKVincentKRLambKMObes 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REVIEWOpenAccessObesityandlongtermfunctionaloutcomes followingelectivetotalhipreplacementHeatherKVincent*,MaryBethHorodyski,PeterGearen,RichardVlasak,AmandaNSeay, BryanPConradandKevinRVincentAbstractIntroduction: Obesityratescontinuetoriseandmoretotalhiparthroplastyproceduresarebeingperformedin progressivelyyounger,obesepatients.Hence,maintenanceoflongtermphysicalfunctionwillbecomevery importantforqualityoflife,functionalindependenceandhipprosthesissurvival.Presently,therearenoreviewsof thelongtermefficacyoftotalhiparthroplastyonphysicalfunction.Thisreview:1)synopsizedavailabledata regardingobesityeffectsonlongtermfunctionaloutcomesaftertotalhiparthroplasty,and2)suggestedfuture directionsforresearch. Methods: Aliteraturesearchwasconductedfrom1965toJanuaryof2011forstudiesthatevaluatedlongterm functionaloutcomesatoneyearorlongerafterTHAinobese(bodymassindexvalues 30kg/m2)andnon-obese patients(bodymassindex < 30kg/m2). Results: Fiveretrospectivestudiesand18prospectivestudieswereidentifiedasthosethatassessedphysical functionbeforesurgeryoutto oneyearaftertotalhiparthroplasty.Studysamplesizesrangedfrom108 – 18,968 andfollowedpatientsfromonetotwentyyears.Totalhiparthroplastyconferssignificantpainreductionand improvementinqualityoflifeirrespectiveofbodymassindex.Functionalimprovementoccurredaftertotalhip arthroplastyamongallstudies,butobesepatientsgenerallydidnotattainthesamelevelofphysicalfunctionby thefollow-uptimepoint. Discussion: Uncontrolledobesityaftertotalhiparthroplastyisrelatedtoworseningofcomorbiditiesandexcessive healthcarecostsoverthelongterm.Aggressiveandsustainablerehabilitationstrategiesthatincludephysical exercise,psychosocialcomponentsandbehaviormodificationmaybehighlyusefulinmaximizingandmaintaining weightlossaftertotalhiparthroplasty. Keywords: Arthroplasty,Bodymassindex,Hip,Physicalfunction,Disability,ObesityIntroductionTheobesesegmentofthepopulationwithosteoarthritisis burgeoning,andthedemandfortotalhiparthroplasty (THA)surgeriestotreatobesepersonsisrisingrapidly.PrimaryTHAprocedureswilllikelybecomenecessaryfora greaterprevalenceoftheU.S.populationwhoisdeveloping debilitatingOAearlierinlife,andrevisionTHAswillbecomemorefrequentastheseyoungadultsageandthelife ofthejointcomponentends.Evidenceindicatesthatthe relativeriskratioforunderg oingelectivehipreplacement rangesfrom1.92inoverweightindividualsto8.56inseverelyobeseindividuals[1].W hileextensiveevidencehas focusedonsurgicaloutcomes,mortalitymedicalcomplicationsafterhipreplacement[2],therelationshipbetween functionaloutcomesandobesityafterTHAoverthelong termisnotwellunderstood,particularlyintheobesepatient.Thisisasignificantscie ntificdeficitasrestorationof physicalfunctionisoneoftheprimarygoalsofTHA[3,4]. AsobesityratescontinuerisingandmoreTHAsare beingperformedinprogressivelyyounger,obesepatients, longtermfunctionalgoalswillbecomeimportant.Functionalgoalsmayincludemaintainingindependencewith loadbearingactivitiesofdailyliving,independentmobility andbodytransfersoverthel ongterm.Manyobesepatients *Correspondence: vincehk@ortho.ufl.edu InterdisciplinaryCenterforMusculoskeletalTrainingandResearch, DepartmentofOrthopaedicsandRehabilitation,DivisionsofResearch,Joint Reconstruction,&PhysicalMedicineandRehabilitation,UniversityofFlorida, Gainesville,FL32611,USA 2012Vincentetal;licenseeBioMedCentralLtd.ThisisanOpenAccessarticledistributedunderthetermsoftheCreative CommonsAttributionLicense(http://creativecommons.org/licenses/by/2.0),whichpermitsunrestricteduse,distribution,and reproductioninanymedium,providedtheoriginalworkisproperlycited.Vincent etal.JournalofOrthopaedicSurgeryandResearch 2012, 7 :16 http://www.josr-online.com/content/7/1/16

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withTHAwillberecommendedtoperformexercise(heavy demandorweightbearingactivity)forweightloss.In addition,progressivelymoreobesepatientswithTHAwill belivinglongerwithajointimplantandmaybeatriskfor failureandpoorerqualityoflifeoverthelongduration comparedwithnon-obesepatients.Forexample,35%of patientswithTHAexperiencesevereactivitylimitationby yearfive;obesitysignificantl ypredictedcompletedependenceonwalkingaidsandisassociatedwithdepressionat follow-up[5].Thephysicalcomponentofqualityoflifeis alsolowerinobesepatientsyearsaftertheprocedure[6-8]. Hence,aclearunderstandingtheeffectofobesityonfunctionaloutcomesafterTHAwill becriticalinestablishing expectationsforthepatientsandcareteamanddevelopmentofstrategiestooptimizephysicalfunctionandindependentmobilityforaslongaspossible.Therefore,the purposesofthisreviewareto:1)provideacurrentsynopsis oftheavailabledataregardingobesityeffectsonlongterm functionaloutcomesafter THA,and2)tosuggestfuture directionsforresearch.SearchstrategyWeconductedaliteraturesearchfrom1965toJanuary of2011inMedline,CochraneControlledTrialsRegister, CINAHL,ScopusandWebofScience.ThesearchstrategyidentifiedstudiesinEnglishthatexaminedtherelationshipsbetweenobesityorBMI,physicalfunctionafter totalhipreplacement.Afunctionalmeasurementofmobility,ambulationortransfersoracomprehensiveselfreporttoolthatassessesphysicalfunctionhadtohave beenreportedaminimumofsixmonthsoffollow-up aftersurgery.Estimatesofobesityhadtohavebeen reportedincludingbodymassindex(BMI),bodyfatpercentageorfatmass.Medicalsubjectheadings(MeSH)/ keywordswithallsubheadingsandasfreetextincluded obesity,obese,mobility,functionallimitation,physical function,bodyfat,adiposity,waistcircumference,total hipreplacementandhiparthroplasty.Studiesthatadministeredsurveysthatreflectedtheperceivedphysical functionalabilitywerealsoincluded;thesetoolsincluded theOxfordHipscore(OHS),HarrisHipscore(HHS), WesternOntarioMcMasterOsteoarthritisIndex (WOMAC)scoreorotherspeciallyconstructedsurveys thatincludedfunction-basedquestions,suchastheUniversityofCaliforniaLosAngeles(UCLA)hipscoring system.Studiesthatusedfunctionaltests(walkingtests, chairriseortimedupandgoorbodytransfersorother selfcaretasks)werealsoincluded.Atotalof552papers wereinitiallygeneratedfromthissearch.Studiesthat hadafollow-upoflessthansixmonths,didnotreport anyformoffunctionalmeasureatfollow-upordidnot includeanassessmentofobesitywerenotincluded.The listsofreferencesofretrievedpublicationsweremanuallycheckedtoaddanycitationsmissedbytheelectronic searches.Obesitywasdefinedasanexcessivebody weight > 100kg,aBMI 30kg/m2[9],oralargewaist circumference( > 88cmwomen, > 102cmmen)[10].CharacteristicsofincludedstudiesAtotalof23articleswerereviewed.Twentyarticles includedself-reportassessmentsoftheWOMAC,HHS orOHSorothersurveybasedtoolsofphysicalfunction. Eightstudiesincludedobjectivephysicalfunctionassessments.StudieswereconductedintheUnitedStates [7,11-13],Europe(Netherlands[14],Scotland[15],the UnitedKingdom[6,16-19],Switzerland[3],Denmark [20]),Canada[2,21]andAustralia[22-25].Studysample sizesrangedfrom140[15]to18,968[3]andwerecomprisedof17-77%women,dependingonthestudy.We identifiedthreemulticenterstudies(twofromBritain, onefromSwitzerland,andonewith7to20sites) [3,16,18]andtwostudiesbasedonjointsurgeryregistries(American-basedregistrystudy)[13]andaCanadianbasedregistry[26]. Severalstudiesdemonstratedvariabilityinthefollow-up timepointsforassessment,whichlimitsgeneralizabilityof thefindings.Forexample,tworetrospectivestudiescapturedfollowupdatafrom0.1-15.6years[14]andfrom 10 – 18.9years[11].Otherretrospectivestudiescaptured follow-uptimesouttooneyear[2]oratdifferentpointsof timeduringtheyearsfollowingthesurgery[7,11,24].A fewprospectivestudiescontainedfollow-updatafromdifferenttimepointsduringyearsfollowingtheprocedure [23,27].HipsurgicalcomponentsandapproachesSurgicaltechnique,componenttypeanduseofcement variedamongandwithintheidentifiedstudies.Several surgicaltechniqueswereusedacrossthestudies,includinganterolateral[6,14,16,19],posterior[7,16,23],lateral [28]andposterolateral[11,20]approaches.Therewas alsovariationinthetypeofcomponentused,andcementuseforfixationofthecomponent.Cementproceduresweredescribedinsixstudies[6,7,14,15,29,30],and twostudiesdescribedamixedprocedureofonecementedcomponentandonenon-cementcomponent[28,31]. Numerousstudiesdidnotreportorclearlydescribethe componentsorthesurgicalprocedure[2,3,13,15,1719,22,24,26,29,32].Onlyafewofthestudiescontrolled thenumberofsurgeonsperformingthearthroplasties, therebyprovidingsomecontroloverthevariationinthe operatingroomprocedures[17,23,24].Therefore,the specificsurgicaldetailswerewidelyvariedamongthe studypool.RetrospectiveevidenceWeidentifiedfiveretrospectivestudies,andthesummariesofthesestudiesarefoundinTable1.ThreeVincent etal.JournalofOrthopaedicSurgeryandResearch 2012, 7 :16Page2of12 http://www.josr-online.com/content/7/1/16

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studiesevaluatedobesityeffectsonHHSscorevalues overvariedfollow-uptimepointsoutto20years.A BMIvalueof > 30kg/m2wasrelatedwitha4-9%lower HHSscoresatfollow-upthanBMIvalueslessthan 30kg/m2[14,24].DespiteHHSscoredifferences,implantsurvivaldurationwassimilarbyyear11.One studythatassessedfollow-upHHSscoresdidnotfind differencesinimprovementlevelsbetweennon-obese andobesepatientsaftertheprocedure[11].Thiscorrespondedwithnodifferencesinrevisionratesormedical complications.Twootherreportsshowedthatpatients withhigherBMIvalueshad4-9%lowerHHSscoresat maximumfollow-uptimeof1 – 10years[14,24],andsignificantlylessrangeofmotionduringhipflexion,adduction,internalrotationandlowerkneeflexionvalues thanpatientswithnormalBMIvalues.Similartothe findingsofMcLaughlinandLee[11],Yeungetal[24] reportednodifferencesintheprobabilityof11yearin implantsurvivalbasedonBMI. Onestudyexaminedwhetherthefunctionalandqualityoflifeoutcomesofhipresurfacingvariedamongnonobeseandobesepatientsusingdataobtainedfromaninstitutionalregistry[7].Datawereobtainedfromclinical visitsatfourmonths,oneyearandannuallyafter Table1Retrospectivestudiesoffunctionaloutcomesinobeseandnon-obesepatientswithtotalhiparthroplasty (THA)StudyNFollow-upSampleSurgicalType&ComponentsResults Braeken etal[ 2 ](1997) 193to1year;Retrospective Meanage63.5years 61%werewomenBMIwas foundforeachpatient Surgicalcomponentsnot described;surgicaltypenot described:dataobtainedfrom medicalchartsandmailings WhilehighBMIwasrelated tohighpostoperativepain levels,BMIitselfwasnota strongcontributortothe regressionmodelfor WOMACfunctionalscore (parameterestimatevalue of0.092). Haverkamp etal[ 14 ](2008) 411Meanoutto20years; Retrospective 69%werewomen;BMIgroups were < 25, 25and > 30kg/m2Meanageswere64 – 66years amonggroups Anterolateralapproach; WeberrotationTHASystem (Allopro)withcement; HHSscoreswereprogressively lowerforhigherBMIbrackets atmaximumfollow-uptime (91.6,86.8and83.7points; p=0.02);revisionrateswere similaramongBMIcomplication ratesandgroups LeDuffetal [ 7 ](2007) 7702 – 10years; Retrospective 17%werewomenBMIgroups were < or 30kg/m2Meanage49years Posteriorapproach;30-37% ofmetaphysealstemfemoral componentswerecemented; ConservePlushipresurfacing prostheseswereused By6.2yearsoffollow-up,UCLA scoresforfunctionandactivity werelowerintheobesepatients thannon-obesepatientsby~8%; SF-12physicalcomponentscores werealsolowerintheobese group(49.3vs51.4points; p=0.013);5yearsurvivorshipwas 90.6%and98.6%inpatientswith BMI < 25and30kg/m2, respectively. McLaughlin &Lee[ 33 ] 28510 – 18years; Retrospective 51%werewomen;BMIgroups were < 30or 30kg/m2Mean ages54 – 57years UncementedT-tapacetabular components(BiometInc.)and Taperlocfemoralpointsinobese patientsandfrom53tocomponents wereusedbyonesurgeon;all wereposterolateralapproaches Byfollow-upHHS from52to 8989pointsinnon-obese patients,withnodifference betweengroups;nodifferences inrevisionratesorcomplications occurredbetweengroups Yeungetal [ 24 ](2010) 2,0266.3yearmean follow-up;Retrospective 53%werefemale;BMIgroups were < 30or 30kg/m2Cementlessproceduresused; componentsandapproachedwere notdescribed HHSscoreswerelowerforthe obesecomparedtothe non-obesepatientsat follow-up(89.9vs93.2points; p < 0.001);HHSscoresfor function,activities,hiprange ofmotionwerelowerinthe obesegroup(allp < 0.05); survivalrateswereforthe implantsweresimilaratyear 11(95-96%)THA=totalhiparthroplasty;BMI=bodymassindex;EUROHIP=EuropeanCollaborativeDatabaseofCostandPracticePatternsofTotalHipReplacement. OR=oddsratio;RR=relativerisk;HHS=HarrisHipScore;UCLA=UniversityofCaliforniaandLosAngeles(UCLA)activityscale;MedicalOutcomesSF-1 2=Short Form12;WOMAC=WesternOntarioandMcMasterOsteoarthritisIndex;VAS=visualanaloguescale. NS=notspecified.Vincent etal.JournalofOrthopaedicSurgeryandResearch 2012, 7 :16Page3of12 http://www.josr-online.com/content/7/1/16

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surgery,withfollow-uptimesrangingfrom2 – 10years. Inobesepatients,post-operativeHHSscorewere3.2 pointslower,UCLAsub-scoresfor “ function ” and “ activity ” were4-7%lowerthanthoseofthenon-obese patients.UCLAsub-scoresof “ walking ” werenotdifferentbetweengroups.Interestingly,survivalofthehipimplantwashigherintheobesepatientscomparedtothe non-obesepatientsbyyear5(98.6%vs90.6%).ProspectiveevidenceTable2summarizestheprospectivestudiesthatweidentified.SixstudiesusedHHSasprimaryendpoints [6,8,15,17,19,28],onestudyusedOHS[16],oneusedthe UCLAactivityscore[31],andsixstudiesemployedthe WOMACsurveyscores[8,18,26,28,34,35]asamainoutcome.Sixstudiesusedactualfunctionalmeasuresand patientreportedfunctionalabilities[3,12,20,23,34,35].HarrishipscoreHHSscoresandfunctionalsub-scoreswerecapturedat avarietyoftimepointsrangingfromonetofiveyears. Inonestudy,sub-scoresofHHSwerereportedinnonobeseandobesepatientswithTHAbythreeyearspostsurgery[15].Sub-scoresofwalkingdistance,climbing stairs,puttingonshoesandsocks,sittingandhiprange ofmotionwere4-25%lowerintheobesegroupatfollow-up.DespitemeanimprovementsinHHSandmobility,thecohorttendedtogainweightbyyearthree. Anotherstudytrackedfunctionalandclinicaloutcomes inagroupofmorbidlyobesepatientswithTHAoutto yearfive;HHSscoresimprovedsignificantlyinall patientsbymonthsix[6].WhiletheHHSscoreswere higherinnon-obesepatientsbyyearfive,theabsolute improvementinscoreswerenotdifferentbasedonobesitystatus(52.0vs48.1pointchange).Also,themorbidly obesepatientshadmoreperi-operativecomplications (12vs3complications)andthefiveyearsurvivalwas 90.9%and100%intheobeseandnon-obesepatients. Bothsexandrevisionstatusmaybeimportantfactors influencingHHSoutcomes.Forexample,HHSscores wereevaluatedamongpatientswithaprimaryorrevisionTHAinaSwisscohort[28].Patientswithrevisions hadarelativeriskof1.67forbeingobese,andBMIwas foundtobeastrongerinversepredictorofHHSafterrevisionproceduresthanprimaryproceduresbyyearfive. Inarelatedstudybythesameauthor[8],HHSscores werecollectedinSwisspatientsfiveyearsafterTHA proceduresandfoundthat81%and70%ofnon-obese andobesepatientshadgoodtoexcellentoutcomes, definedasaHHSscore 80points.Thesepooreroutcomesweremagnifiedinwomenthanmen.Forexample, HHSscoresinnon-obeseandobesewomenwere87.8 and79.6pointsrespectively,andwere90.5and87.4 pointsinnon-obeseandobesemen. Amongpredictiveandcorrelationalstudies,Moranetal [19]examinedwhetherBMIpredictedHHSscoresatfollow-uptimesofsixand18monthspost-THA.Whileno BMI-specificHHSdatawerepresented,theauthors reportedasmallbutsignificantmultipleregressioncoefficientforBMIonthemodelforthefollow-upsHHS.This translatedtoareductioninHHSby0.25-0.35pointsper onepointincreaseinBMIvalue.Anothercorrelational studythatweincludeddidnotreportactualHHSscores, butsuperimposedHHSscoresontotheRosserDisability Indexmatrixtogeneratea “ qualityoflife ” scoreasa methodofestimatingfunctionaldisability[17].Thefindingsrevealedthatthemedianqualityoflifescoreswere notdifferentamongpatientswithlowandhighBMIvalues atoneandthreeyearsoffollow-up[17].TheauthorsconcludedthatprogressivelyhigherBMIvaluesupto40kg/ m2werenotrelatedwiththesedisabilityestimates.WOMACscoresOnestudyexaminedthepredictivevalueofonetofourfactorsrelatingtothemetabolicsyndromeonWOMAC scoresbeforeandatoneyearafterTHA[26].Thesefactors includedlargewaistcircumference( > 102cmmen, > 88cm women),elevatedtriglyceridesandlowhighdensitylipoproteincholesterol,highbloodpressureandelevatedfasting bloodglucose.BMIwascalculatedforeachpatient.Regressionanalyseswereperformedtodeterminetheeffectofthe numberofmetabolicsyndromefactorsonWOMACscores byyearone.Theregressionbetacoefficientofhaving4 metabolicfactorsonpredictionofWOMACscoreswas 16.1inthisobesepatientgroupcomparedwiththebetacoefficientof0.6innon-obesepatientswithonefactor.The coefficientforobesityalonewas2.4(p=0.03). AstudythatanalyzeddatafromtwelveEuropean countriesshowedthatoneyearWOMACscoresare relatedtoBMI[18].MedianbaselineWOMACscores werehigherinmorbidlyobeseandobesepatientscomparedwithnon-obesepatients(68.1and61.5vs57.6 points)butthemedianchangeinWOMACscoreswas highestinthemorbidlyobesegroupbyyearone(56.1vs 33.3and37.5points;p=0.012).Inthiscohort,themultivariateoddsratioofreturningtonormalfunctionalstatuswas3.1comparedtonon-obesepatients. Lubbekeetal.performedtwohospital-basedcohorts examiningthe1)fiveyearoutcomesinobesemenand womenwithTHA[8],and2)theeffectsofcomorbidities andageafterprimaryandrevisionTHA[28].Inthefirst study,sexdifferencesinsurveyoutcomeswereanalyzedin acohortofpatientswithTHA.Thecrudeincidencerate was4.7timeshigherforinfection,andtheincidencerate was2.3timeshigherfordislocationinobesepatientscomparedtonon-obesepatients.Five-yearWOMACfunction sub-scoreswere11%lowerinobesewomenthanmenand 8%lowerinnon-obesewomenthanmen.WithineachsexVincent etal.JournalofOrthopaedicSurgeryandResearch 2012, 7 :16Page4of12 http://www.josr-online.com/content/7/1/16

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Table2Prospectivestudiesoffunctionaloutcomesinobeseandnon-obesepatientswithtotalhiparthroplasty(THA)StudyNFollow-upSampleSurgicalType& Components Results Aderintoetal[ 15 ] (2005) 1403years;Prospective Follow-up 61%werewomen; groupswere < 30or 30kg/m2Cementedprostheses; approachesorcomponents werenotdescribed Atyear3,HHSscores from44to 90points(non-obese)andfrom 42.5to85points(obese),withno differencebetweengroups;lower scoresforstairs,sittingandputtingon shoes-socksandrangeofmotion werelowerintheobesepatients (p < 0.05). Andrewetal[ 16 ] (2008) 1,4215years;MulticenterProspective 62%werewomen; BMIgroupswere < 30,30< 40and 40kg/m2Mean ageswere69.1,65.5 and60.6years Anterolateralorposterior approacheswereused; cementedStrykerExeter femoralcomponentsand severaldifferentacetabular components Byyear5,OHSscoreswere bestinthenon-obesegroup andworstintheobesegroup (19.6vs25.6points;p=0.005), butnodifferencesinthe5year changeinOHSscoresexisted. Nodifferencesinratesofrevision, dislocationsormedical complicationsexisted. Busatoetal[ 3 ] (2008) 18,96815years;Multicenterprospective sexesNS;BMIgroups were < 25,25< 30 and 30kg/m2Surgicalcomponentsnot described;surgicaltypenot described;Datawere obtainedfromtheTotalHip Registry(Switzerland) HighpreoperativeBMIwasrelated withadose-effectresponsewith shorterunsupportedwalking timelessnormalstairclimb,and shoetyingduringthe15year follow-up,despitesimilarpain reliefacrossBMIbrackets. ChanandVillar[ 17 ] (1996) 166to3years; Prospectivecohort 59%werewomenBMI groupswere < 25, 25 – 29.9,30 – 39.9, > 40kg/m2Meanages were71.4,69.0and 68.1years Surgicalcomponentsnot described;surgicaltype notdescribed HHSscoresweresuperimposed ontotheRosserIndexMatrix (whichranksdisabilitystatus);there werenodifferencesinRosserscores fordisabilityamongtheBMIgroups byyear3. Cheeetal[ 6 ] (2010) 1085years;Prospective cohort 41%werewomen;BMI groupswere < 35kg/m2or > 35(1comorbidity) and > 40kg/m2Anterolateralapproachwas usedonallpatients;25.5% Charnleyprosthesis (dePuy,Int.),74.5%Lubinus SPIIprosthesis(Waldmar-Link GmbH);cemented FiveyearHHSwerehigherin non-obesethanmorbidlyobese patients(91.8vs85.4points; p < 0.0001)despitesimilarpreoperativescores;SF-36subscores forphysicalfunctioningwerelower inmorbidlyobesepatientsat year5. Dowseyetal[ 29 ] (2010) 4711year;Prospective follow-up 60%werewomen;BMI groupswere < 30,30 – 39 and 40.0kg/m2 Surgicalproceduresnot described;surgicalcomponents notdescribed;cementused variedacrossgroups Morbidlyobesepatientshada lowerchangeinHHSfunction scoresthanobeseandnon-obese patients,respectivelybyyear 1(11.5vs15.6and16.2points, respectively);HHSwerelowest inmorbidlyobesepatientsby year1(70.5vs79.8and80.8 pointsp=0.03). Gandhietal[ 26 ] (2010) 707hipsIyear Prospectivecohort 59-66%werewomen; waistcircumferencewas assessedformetabolic syndromeBMIranged from22.0to36.6kg/m264.8-66.2years Surgicalcomponentsor proceduresnotdescribed; patientswereobtained fromaregistry 1yearWOMACscores(pain,function) werehighestinpatientswith4 metabolicsyndromefactorscompared tothosewithfewerfactors;regression Bcoefficientsshowedthatobesity predicted1yearWOMACscores (B=2.41.4-4.2;95%CI). Jacksonetal[ 23 ] (2009) 2,026meanof5years; Prospectivecohort 77%werewomen; BMIgroupswere Meanageswere68 and63years Posteriorsurgicalapproach; ABG2Strykercementless femoralandacetabular components HHSwerelowerinobesevs non-obesepatientsatfollow-up (89.9vs93.2points);HHSfunctional scoreswerealsolowerinthe obesegroup(29.6vs31.0points); hipflexion,adductionandinternal rotationrangeswerelessinthe obesevsnon-obesepatients.HHS painscoreswerenotdifferent betweengroups. Vincent etal.JournalofOrthopaedicSurgeryandResearch 2012, 7 :16Page5of12 http://www.josr-online.com/content/7/1/16

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Table2Prospectivestudiesoffunctionaloutcomesinobeseandnon-obesepatientswithtotalhiparthroplasty(THA) (Continued)Judgeetal[ 18 ] (2010) 1,3271yearEUROHIP Studyof20orthopedic centers 56%werewomen; BMIgroupswere < 30, 30 – 39and 40kg/m2Ages < 50to 70years Surgicalcomponentsnot described;surgicaltype notdescribed MedianWOMACscoreswerehighest inthemorbidlyobesegrouppre-THR, (68.1vs61.5and57.6points). butthe1yearchangeinWOMAC scorewashighestinthemorbidly obesegroup(medianscorechange of56.1vs33.3and37.5points); morbidlyobesepatientsshowed a ORof “ returningtonormal ” (functionality)thantheothergroups. Lubbekeetal[ 28 ] (2007) 4355-year;Prospective cohort 53-55%arewomen; BMIgroupswere < or 30kg/m2Meanageswere 6872years 85%ofpatientshadmixed components (1cemented,1non) Obesitywasrelatedwithworse outcomesafterrevisionthanprimary THAbyyear5(lowerHHSscores:76.7 vs88.1points;lowerWOMACfunction scores61.6vs70.0points).BMIwas relatedtothemeandifferenceof HHSscoresforprimaryandrevision THA(Rcoefficient= Š 1.0 [ Š 0.1to Š 1.95%CI]). Lubbekeetal[ 8 ] (2007) 2,4955-year;Prospective cohort 48.7-57.5%women; 8.5-9%wererevisions; BMIgroupswere < or 30 kg/m2Meanage69years 95%werelateralTHAapproach, 86%usedMorscherpress-fit uncementedactetabular componentandMuller straightstemcobaltchromium femoralcomponent BMIof 30kg/m2wasrelatedwitha RRof3.7-4.0forrevisions,9.1-12.5for dislocationsand1.9-8.0forinfections inobesecomparedtonon-obese menandwomen.Byyear5,HHS were87.8and79.6pointsinnonobeseandobesewomenand90.5 vs87.4pointsinnon-obeseand obesemen;WOMACfunction scoreswere14.7%and8.0%lower inobesewomenandmenthantheir non-obesecounterparts. Lubbekeetal[ 30 ] (2008) 2045-year;Prospective cohort 50-7.9%werewomen; BMIgroupswere < or 30kg/m2Age range < 50to 80years Cementedacetabularcups wereusedin67%and80% ofobeseandnon-obese patients HHSwere82.814.7and71.417.0 pointsinthenon-obeseandobese patientsbyyear5.Surgicalrevisions wereperformedat92and125months inobeseandnon-obesegroups, respectively.Thead justedhazardratio foroccurrenceofinfection,dislocation orre-revisionincreasedfrom1.0 (BMI < 25)to1.5(BMI25 – 29.9)to 4.5(BMI30 – 34.9)to10.9(BMI 35.0). Lubbekeetal[ 31 ] (2010) 5035or10years; Prospectivefollow-up 58%werewomen;BMI groupswere < 25,25 – 29.9 and 30kg/m2Hybridprosthesis;Morscher pressfituncementedcupand cementedcobalt-chromium stem(Zimmer);alumnia ceramichead,andaceramicpolyethylenesurface Atyear5,HHS # witheachrogressively higherBMIgroup(91.4,88.4and85.1 points;p=0.019).Atyear10,HHS tendedtobelowerinpatientswith BMI 30kg/m2comparedwiththose withBMI < 25and25 – 29.9kg/m2(83.6vs87.3and87.1points;p=0.08); moreobesepatientshadlowUCLA scoresandmorenon-obesepatients hadhigherUCLAscores. Moranetal[ 19 ] (2005) 8006 – 18mo;Prospective follow-up 61%women;BMIgroups were < 25,25 – 29.9, 30 – 39.9 40kg/m2Mean agewas68years Allwereanterolateral approachsurgeries; componentswerenot described Forevery1pointincreaseinBMI, HHSscoresdroppedby0.25by month6andby0.35bymonth 18post-surgery.NoBMIeffecton earlyfailureofTHAwasfound. Nayloretal[ 22 ] (2008) 1981year;Prospective observational 56%werewomen;BMI groupswere < 30 or 30kg/m2Mean age67years Surgicalcomponentsnot described;approaches notdescribed Obesepatientshadsmallerincreases intimedmobilitythannon-obese patients(0.23m/ssloweron15m walktime)andthetimedupand gotest(3.1secslower)atyear1; WOMACscoresforfunctionand painwereworseinobesethan non-obesepatientsbyyear1. Vincent etal.JournalofOrthopaedicSurgeryandResearch 2012, 7 :16Page6of12 http://www.josr-online.com/content/7/1/16

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group,obesewomenandmenhad8-11%lowerWOMAC functionsub-scoresthantheirnon-obesecounterparts.In thesecondstudy,patientswithprimaryandrevisionprocedureswereadministeredtheWOMACatfiveyears[28]. ofnote,thepatientswithrevisionsweremoreoftenobese thannot.TheWOMACfunctionsub-scorewasreported tobelowerinobesepatientswithrevisionTHAcompared withnon-obesepatients(61.6vs70.0points).Thisdifferencewasdeemedsmallbutclinicallysignificant. AsampleofAustralianpatientswithprimaryunilateral THAwasanalyzedfordifferencesinWOMACresponses byyearone[34].TheobesepatientsreportedimprovementsinWOMACfunctionsubscoresfrom44.6to23.3 pointswhilethenon-obesepatientsdemonstrated improvementsinthissamesubscorefrom40.7to13.7 points.Hence,thenon-obesepatientsshowedagreater relativefunctionalimprovementthanobesepatientsat yearone.Sticklesetal[35]prospectivelyassessed WOMACresponsesinpersonswithTHAacrosstheBMI spectrum: < 25,25 – 20,30 – 35,35 – 40and > 40kg/m2.At oneyearaftersurgery,WOMACscoreswereprogressively lesswitheachhigherBMIbracket.TherewerenodifferencesamongBMIbracketsinthetotalcomplicationrate, medicalcomplicationrateororthopediccomplication rate.Oxfordhipscores(OHS)OnestudypresentedresponsestotheOxfordHipsurvey ingroupswithlowandhighBMIs.Andrewetal.[16]. comparedtheOHSinnon-obese,obeseandmorbidly obesepatientspre-surgery,threemonthsandannually untilyearfive.Byyearthree,theaverageOHSwashighestinthenon-obesegroupandlowestinthemorbidly obesegroup(19.68.6vs23.511.4points);thispattern wasmaintainedouttoyearfive.However,thefiveyear changeinabsoluteOHSwasnotdifferentbasedonBMI, indicatingcomparableresponsivenesstotheprocedure overthelongterm.Therewerenodifferencesinthe ratesofperisurgicalmedicalcomplicationsorlongterm femoralstemposition,femoralosteolysisorimplant survival.UCLAactivityscoreAprospectivestudythatcomparedtheosteolysisrates andpatientsatisfactionafterTHAwasconductedby Lubbekeetal[31].Thepatientactivitylevelwasassessed usingtheUCLAsurveyatthepre-surgerytimepoint andatyearsfiveandtenafterTHA.Patientswerestratifiedintonon-obese,overweight,andobesegroupsbased onBMI.WhilethemeanUCLAscoresweresimilarbetweengroupsatfollow-up,the6.8%ofobesepatients Table2Prospectivestudiesoffunctionaloutcomesinobeseandnon-obesepatientswithtotalhiparthroplasty(THA) (Continued)Singhetal[ 12 ] (2009) 2,6872 – 5years;Prospective cohortofrevisionTHA 53-54%werewomen;BMI bracketswere < 25, 25 – 29.9,30 – 39.9 40kg/m2Mean5yearage was65years Surgicalcomponentsnot described;approaches notdescribed Atyear2,theORforcomplete dependenceonwalking/gaitaids was2.0(vs0.9forBMI25 – 29.9); moderatetosevereactivity limitationwaspredictedby highBMI.TheORofreporting difficultyin3of7mobilityand functionaltasks from1.2to2.7 withincreasedBMIfrom25 – 29.9 to40kg/m2,byyearfive,theOR increasedto1.3and3.0inthese sameBMIbrackets(allp < 0.01). Sballeetal(1987) [ 20 ] 1255years; Prospectivefollow-up Aweightindexwas calculatedas < or > 120% ofpre-surgicalweight; analyseswerealso performedusingweight bracketsof < or > 80kg; Meanageatfollow-up 70(28 – 89)years Allwereposterolateral approachsurgeries; Lubinusprostheses wereusedandfixedwith gentamicinimpregnated radiopaquePMMA;One surgeonperformedallhip replacements Walkingability,definedusingthe Charnleyscoringsystemwaslower inpatientswithaweightindex > 120 pre-surgery,butsimilartopatients withindexes < 120byyear5 (4.9vs5.0points;p=NSig). Sticklesetal[ 13 ] (2001) 5921year;Prospective follow-up 56%werewomen;BMI bracketswere < 25, 25 – 29.9,30 – 40 > 40kg/m2Meanage69years Surgicalcomponentsor proceduresnotdescribed; patientswereobtained fromaregistry Byyear1,stairascensionand descensiondifficultywasreported in86-88%ofveryobesepatients comparedwith46-55%of non-obesepatients;BMIdidnot correlatewithchangeinWOMAC scores(31.8and35.9points,in non-obeseandveryobese patients,respectively;p > 0.05).THA=totalhiparthroplasty;BMI=bodymassindex;EUROHIP=EuropeanCollaborativeDatabaseofCostandPracticePatternsofTotalHipReplacement. OR=oddsratio;RR=relativerisk;HHS=HarrisHipScore;UCLA=UniversityofCaliforniaandLosAngeles(UCLA)activityscale;MedicalOutcomesSF-1 2=Short Form12;WOMAC=WesternOntarioandMcMasterOsteoarthritisIndex;VAS=visualanaloguescale. NSig=non-significant.Vincent etal.JournalofOrthopaedicSurgeryandResearch 2012, 7 :16Page7of12 http://www.josr-online.com/content/7/1/16

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achievedahighactivityUCLAscorecomparedto11.7% overweightand14.4%ofnormalweightgroups.This findingwascorroboratedwithlowerfollow-upHHSin theobesegroupcomparedtotheremaininggroups. Obesepatientshadpoorerpainscoresandanoddsratio of1.44ofdevelopingfemoralosteolysiswhereasthenormalweighthadanoddsratioof2.64comparedtothe referenceoverweightgroup.FunctionaltestsSeveralstudiesassessedfunctionalcapacitywithwalking tests,stairclimbing,andtimedfunctionaltests.Inan earlystudy,walkingabilitywasaprimaryfunctionalfive yearendpointforaDanishcohortofpatientswithTHA [20].Radiographicandsurgicaloutcomesweremeasured inadditiontowalkingability.TheCharnleycriteria[36] wereappliedtowalkingability(6points=walking,no limp;5points=extensivewalking,withorwithoutcane, withlimp;4points=moderatewalkingwithonecrutch orcane;3points=restrictedwalkingwithcrutches;2 points=wheelchairtransferactivity;1point=bedridden) beforeandafterTHA.Patientswerestratifiedbasedona weightindex( < or > 120%ofnormalweightforheight andsex)orbybodyweight( < 80kgor > 80kg).Pre-operatively,walkingabilityscoresweredifferentbasedon %ofnormalweight(1.8vs2.3pointsinheavyversus non-heavypatients,respectively;p < 0.05)butnotabsolutebodyweight(2.2pointsforbothgroups).Fiveyears post-THA,Charnelywalkingscoreswerenotdifferent basedoneitherexpressionofbodysize.Whilesurgical bloodlosswasgreaterinheavypatientscomparedwith non-heavypatients,therewerenosignificantdifferences inoperationtime,medicalcomplicationsorlooseningof theimplantbasedonweight. Nayloretal[34]inAustralia,performedshortfunctional testsinobeseandnon-obesepatientsbeforeandatvarious timepointsouttoyearone.Thesetestsincludeda15meterwalkingtestandatimed-up-and-go(TUG)test whereanindividualrisesfromachairandreturnstothe chair.Whileobesitydidnotprecludeimprovementin15 meterwalkingspeed,thetrajectoryofchangewaslowerin theobesegroupbyyearone,andfinalwalkingspeedswere 1.37m/sand1.14m/sinnon-obeseandobesepatients,respectively.Similarly,improvementsinTUGtesttimewere slowerintheobesegroupbyyearone(finalTUGtimes were9.2secand12.4secinthenon-obeseandobese patients).Theapproximate30%an42%improvementsin walkandTUGtimeswerenotdifferentbasedonobesity status.Therewasa2.8%greaterchancethatobesepatients woulduseawalkingaidatfollow-upcomparedtononobesecounterparts. DifficultyascendinganddescendingstairswasoneendpointinaprospectivestudyofAmericanpatientshipor kneearthroplasty[35].AmongthepatientswithTHA,and itwasshownthatthepercentageofpatientsineachprogressivelyhigherBMIbracket( < 25to > 40kg/m[2]) reporteddifficultywithdescendingandascendingstairs. Thisfunctionalpatternwascorroboratedwithself-report WOMACdata,whichshowedlowerscoresintheoneyear totalWOMACscoreandrelatedphysicalcomponentsubscoreinseverelyobesepatientscomparedtonon-obese patients.Totalmedicalcomplicationratewasnotdifferent acrosstheBMIspectrum.However,amajorlimitationto thestudywasthatthespecifictechniqueusedtocapture thisstairclimbinginformationwasnotpresentedinthe methods. InacohortofAmericanpatientswithrevisionTHA,activitylimitationanddependenceonwalkingaidswas assessedbySinghetal[12]atyearstwoandfivepostTHA.Theevidencerevealedthattheoddsratioofdevelopingmoderate-severephysicalactivitylimitation increasedfrom1.2to2.7inoverweightandmorbidlyobese patients.Severeobesityincreasedthetwoandfiveyear oddsratiosofdevelopingcompletedependenceonwalking aidsto2.0and2.7comparedwiththereferenceofnormal weight. Busatoetal[3]collectedaseriesoffunctionalmeasurementsinacohortofSwisspatientswithTHAatperiodic follow-ups,includingwalkingdistancewithoutsupport, hipflexionrange,stairclimbingandputtingonshoesand socks.Datawerereportedasthepercentofpatientswho wereabletoachievewalking > 60minutes,hipflexion range > 90andcapacityfornormalstairclimbanddonningoffootwear.Irrespectiveoftimepoint,fewerobese patientswereabletowalk > 60minuteswithoutsupport andthispercentagecontinuedtolowered27.2%fromyear threetoyear12comparedwiththe18.5%fewernon-obese patients.Thissamepatternoccurredwithstairclimbing andwithtyingshoesbyyear12.Interestingly,theobese patientsincreasedthehipflexionrangeofmotionby7.8%, whereasthenon-obesegrouplost11.6%ofhipflexionmotionbyyear12.InallthreeBMIstrata,painreliefwas achievedinthemajorityofpatientsandwaslargelymaintainedbyyear12. Hiprangeofmotionwasassessedinnon-obeseand obesepatientswithcementlessTHAatamedianfollowuptimeof5.1yearsinadditiontopainratings,survey scoresandimplantsurvival.Despiteequivalentimplant survivalratesbetweengroups,obesepatientsachieved 9.4lessrangeofmovementaboutthehipthannonobesepatientswithflexion,2lessadductionand2.8less ofinternalrotation.Interestingly,painreliefandpatient satisfactionwiththeprocedureweresimilarbetween groupsatfollow-up.OverviewofthefindingsOftheevidenceincludedinthisreview,thesurgical component,cementationorsurgicalapproachdidnotVincent etal.JournalofOrthopaedicSurgeryandResearch 2012, 7 :16Page8of12 http://www.josr-online.com/content/7/1/16

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appeartohaveanyconsistenteffectonlongtermfunctionaloutcomesintheobesepatient.Ofthe23studies, 16reportedthatobesitywasassociatedwithlowerhip functionsurveyscoresatfollow-up,whereasfourstudies didnot.Fivestudiesrevealednegativelongtermeffects ofobesityonvarioustasksofphysicalfunction,andone studynotednoadverseinfluenceofobesityonwalking ability.Whileobesitydoesnotnecessarilyprecludefunctionalimprovementsaftersurgery,thefunctionalgains achievedandtheself-reportedfunctionalabilitygenerally arelowerthanthoseattainedbynon-obesepatients. Thus,evidenceindicatesthatthereissignificantpainreliefandpatientsatisfactionafterTHAinobesepatients, whereasthesepatientsfallshortofachievingthesame longtermfunctionallevelastheirnon-obesecounterparts.Hence,inatimeframeofasshortasoneyearafter THA,obesepatientsarealreadyatafunctionaldeficit comparedtonon-obesecounterparts.Potentialexplanationsforfunctionaloutcomesintheobese patientSomepostulatedmechanismsunderlyingthisfindingincludefearofmovementandfearavoidanceofphysical activities,poorskeletalmusclequality,elevatedperceived effortwithphysicaltasks,andmaintenanceofpre-surgicalphysicalactivitypatterns.Ourresearchlaboratoryhas recentlyshownthatobesepatientsfearpaininducedby physicalactivityandmovement,andthiscorrespondsto lowerself-reportedphysicalabilitieswithtasksrelatedto mobility(e.g.,walking,stairclimbing,bodytransfersand recreationalactivitiesthatinvolverunning,startandstop motionsandjumping)[37,38].Despiteapaucityofliteratureaddressingtheinteractionsofpain,obesityand jointfunctionoverthelongterm,obesepatientscan achievehighsatisfactionandpainreliefandstillnotincreaseparticipationinphysicalactivitiesathomeandin thecommunity.Whetherthisisduetoresidualfearof movementandavoidanceofactivitiesthatmaytrigger painisunknown. Musclestrengthratherthanmusclemassmaybea moreclinicallyrelevantdeterminantoffunctionalstatus intheolderpopulation[39].Adiposetissueitselfcontributestomusclelossthroughchronic,lowgradeproductionofinflammatorycytokines,adipokinesandfreefatty acids[40].Thesechemicalsslowlyerodemusclemassin theolderobeseadult,unfavorablyshiftingtheratioof musclemasstofatmass.Inaddition,existingmuscles becomeinfiltratedbyfat[41],therebyloweringmuscle qualityandfunctionalabilityofthemuscletissue.Residualpost-operativestrengthdeficitsandfatinfiltration mayoccurinthehipflexors(15%strengthdifference comparedtonon-repairedhip)outtotwoyears[42]; thesedeficitsmaycontributetolowerfunctionalability withtasksthatactivatethesemuscles.Hence,independent fromtheimprovementsinpainandqualityoflifeaftera totalhipreplacement,theobesepatientmaynotachieve thesameleveloffunctionasnon-obesepatientinpartdue toskeletalmusclequality,especiallyifthepatientdoesnot changephysicalactivitypatternstoactivateloadingbearing musclegroupsafterTHA. Thelevelofperceiveddifficultyandeffortwithphysical activityisacriticalissueforobeseindividuals,especially thosewithBMI 40kg/m2.Morbidlyobesepatientshave poorcardiac,metabolicandventilatoryefficiencyandhave lowercompensatoryhyperventilationwithexercise[43].A givenexerciseworkloadmayrequirealotofenergyto moveheavierlimbsegmentsagainstgravityinthemorbidlyobeseindividuals(manifestedaslowermechanicalefficiency)[44,45].Self-reportedfatigueishigherwith increasingBMI[46].Mobilityrelatedtasks,suchasshort andlongdistancetimedwalkingtests,stairclimb.TUG testsareconsistentlymorechallengingandtakelongerto performwithincreasingBMI[47].Musculoskeletalpain mayoccurathighintensityactivitiesandmaybethelimitingfactorandnottruemusclefatigue[45].Collectively, thehigherperceptionofmusculareffortanddiscomfortof dyspneamaydiscouragethispopulationfromregularlyengaginginphysicalactivities. Whilequantitativeevidenceofphysicalactivitypatterns afterTHAinobeseadultsissparse,Donovanetal[48]. reportedthatpatientperceptionsofphysicalactivity improvedbyoneyearaftersurgery.Atotalof43%and9% ofthepatientsfeltthattheiractivitylevelimproved “ alot more ” and “ alittlemore ” sincepriortojointreplacement, respectively.Themajorityofthereferencedstudies,however,showedthatweightgainormaintenancetypically occursafterTHA,inferringthatphysicalactivitylevels werenotdramaticallyalteredfrompre-surgicallevels.It hasbeenpostulatedthatwiththeresolutionofhippain anddecreasedneedforanalgesics,normalappetitesand caloricintakereturnedandcounteractedanypotentialeffectofincreasedphysicalactivityintheobesepatient[49].DoesweightlossafterTHAimprovelongtermfunctional outcomes?TheassumptionthatTHAwouldreducehippain,and thereforefosterincreasedphysicalactivityandweight lossintheobesepatientisnotpresentlysubstantiatedby thelimitedevidence.Infact,severalstudiesreportmaintenanceofcurrentweight[48]orcontinuedweightgain (rangingfrom2.5%-3.6%increaseinBMI)onetotwo yearsafterTHA[49-51].Datasuggestthat 75%of patientsexperienceweightgainoverthreeyears[15]. Thistrendoccursinmenandwomen,irrespectiveof pre-surgicalBMI[50].However,inoneprospective study,theaverageweightgainbyoneyearwas2.8kg, withthechangeoccurringprimarilyinwomen[52].In anotherstudy,non-obeseandobesepatientsdidnotloseVincent etal.JournalofOrthopaedicSurgeryandResearch 2012, 7 :16Page9of12 http://www.josr-online.com/content/7/1/16

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weight,whileoverweightpatientsgainedasignificant amountofweightaftersurgery[53].Post-surgicalBMI valuesatfollow-upwereindependentofimprovementin mobilityusingWOMACscore[51]orself-reported improvementsinmobility[54].WesurmisethatthemajorityofpatientsundergoingprimaryTHAwillincrease theirBMIgivensufficientfollow-uptime,irrespectiveof theoutcome[51].Furtherinvestigationofstrategiesthat canbeusedtoencourageperioperativeweightlossand slow,safeweightlossaftersurgerywillbeimportantfor functionalchangeandpreservationofthejointprosthesislifespan.ClinicalimplicationsObesepatientswithTHAarelessfunctionalthannonobesecounterparts.Ifovertimetheobesepatientfailsto modifylifestyle,sarcopenicobesityworsensasaspiralof deconditioningandfunctionaldependencedevelops.The abilitytogeneratemusclestrengthandpowerwilldeclinewithoutparticipationinphysicalactivity.Asthe obesepatientagesandthenegativelifestylebehaviorsremain,obesity-relatedcomorbiditieswillworsen.Additionaljointpainswilldevelopandthejointimplantwill ultimatelyfailearlierinlife.Uncontrolledobesityafter THAwillresultincostlyandcomplicatedsurgicalrevisionprocedures.Thisisaseriousissue,becausethe numberofTHAperformedearlierinobesepatientsis growingrapidlyintheU.S.Possiblesolutionstothis combatthisprobleminclude:1)astrongemphasison aggressiverehabilitationafterTHAthatfocusesonlong termmaintenanceofskeletalmusclequalityandmass, and2)consistent,safemonitoredweightlossoverthe monthsfollowingthesurgerytofacilitatephysicalfunctionandlongevityofthejointimplant.LimitationstotheevidenceThereareseverallimitationsthatdeservecomment. First,thedeterminationof “ physicalfunction ” varied widelyacrossthestudies.Inthispopulation,thereisnot yetastandardtestbatteryperformedbeforeandafter surgery.Second,thereviewedstudiestypicallydidnot reportseverityorfrequencyofothermusculoskeletal painthatmightbeaffectedbyTHA.Thisissueisimportant,asthehipjointliescentrallytothelowerbody kinematicchain.Correctionofhippainmayimprove gait,postureandambulation,therebyreducingother jointsymptomsinthespineandknee.Weassumethat correctionofpainanddisabilityinthehipisthemechanismunderlyingfunctionalimprovement,particularly inobesepatients,butweareneglectingtoaddress whetherTHAhaswiderreachingeffectsonoveralljoint mechanicsandpainsymptoms. Asubstantialattritionrateoccurredinmanystudies. Attritioncreatesselectionbiasofthepopulation,andin manystudiesitwasnotclearhowmissingdatawere handled.Insomecases,onlycompleterswereincluded intheanalysis.Interpretationoflongtermresultsisconfoundedbythelikelihoodofselectionbias.Thelackof emphasisonclinicalimportancehasledtomisconceptionsanddisagreementsabouttheinterpretationofthe resultsofclinicaltrialsandatendencytoequatestatisticalsignificancewithclinicalimportance.Insome instances,statisticallysignificantresultsmaynotbeclinicallyimportantand,conversely,statisticallyinsignificant resultsdonotcompletelyruleoutthepossibilityofclinicallyimportanteffects[55].FuturedirectionsTheNationalHealthandNutritionExaminationSurvey IIIdatashowthatlowerbodyfunctionalimpairmentis becomingmoreprevalentinobeseindividuals;among obesepersons,36.8%reporteddisabilityin1994,whereas 42.2%reporteddisabilityandfunctionalimpairmentin 2004[56].Developmentofabatteryoffunctionaltests ofhipflexibility,muscletestingandmobilityshouldbe standardpracticeforTHAresearchtohelppredictfunctionalsuccessofthesurgery.Acomprehensivepainand fearassessmentwillhelpdeterminehowsystemicpain relatestothesymptomsandchangesinthehipjoint. Prospectivebiomechanicalassessmentsoflowerbody kinematicsinthesurgicalandnon-surgicallimbwould beveryusefulintrackingthelongtermjointmotionand physicalcapabilities.Psychiatric[57],psychosocial[58] andbehavioraltraits[59]orgeneticphenotypes[60] associatedwithsevereobesityshouldbefactorstotrack infutureoutcomesstudies.Thereisadireneedforidentificationofspecificexercise,psychosocial,painmanagementandnutritionalinterventionsthateffectively enhancegainsmadeinphysicalfunctionoverthelong term.Finally,itwouldbeclinicallyimportanttodeterminewhatamountofweightlossmaximizesimplant lifespan.ConclusionsTHAconferssignificantpainreductionandimprovement inqualityoflifeirrespectiveofBMI.WhilefunctionalimprovementoccursafterTHA,availableevidenceindicates thatobesepatientsarelesslikelytoattainthesamelevelof physicalfunctionoverthelongterm.Uncontrolledobesity isrelatedtoworseningofcomorbiditiesandexcessive healthcarecostsoverthelongterm.Aggressiveandsustainablerehabilitationstrategiesthatincludephysicalexercise,psychosocialcomponentsandbehaviormodification maybehighlyusefulinmaximizingandmaintaining weightlossafterTHA.Furthermore,thistypeofrehabilitationmayalsoreducetheoverallhealthcareburden.Vincent etal.JournalofOrthopaedicSurgeryandResearch 2012, 7 :16Page10of12 http://www.josr-online.com/content/7/1/16

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Competinginterests Theauthorsdeclarethattheyhavenocompetinginterests. Authors ’ contributions HVprimarywriter.MBHtextcontributor,editing.PFGtextcontributor, editing.RVtextcontributor,editing.ANScollectionofscientificpapers,text contributor.BPCtextcontributor,editing.KRVtextcontributor,editing.All authorsreadandapprovedthefinalmanuscript. Acknowledgements ThisworkhasbeensupportedbytheUniversityofFlorida ’ sInterdisciplinary CenterforMusculoskeletalTrainingandResearch,Departmentof OrthopaedicsandRehabilitation. Received:9March2011Accepted:2April2012 Published:25April2012 References1.BourneR,MukhiS,ZhuN,KeresteciM,MarinM: Roleofobesityontherisk fortotalhiporkneearthroplasty. ClinicalOrthopedicsandRelatedResearch 2007, 465: 185 – 188. 2.BraekenAM,Lochhaas-GerlachJA,GollishJD,MylesJD,MackenzieTA: Determinantsof6 – 12monthpostoperativefunctionalstatusandpain afterelectivetotalhipreplacement. 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PM&R 2010, 2 (8):713 – 722. 38.VincentHK,OmliMR,DayTI,HodgesM,VincentK,R.,GeorgeSZ(2011)Fear ofmovement,qualityoflifeandself-reporteddisabilityinobesepatients withchroniclumbarpain. PainMedicine. Inpress 39.StenholmS,HarrisTB,RantanenT,VisserM,KritchevskySB,FerrucciL: Sarcopenicobesity:definition,causeandconsequences. CurrentOpinions inClinicalNutritionandMetabolismCare 2008, 11 (6):693 – 700.Vincent etal.JournalofOrthopaedicSurgeryandResearch 2012, 7 :16Page11of12 http://www.josr-online.com/content/7/1/16

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Abstract
Introduction
Obesity rates continue to rise and more total hip arthroplasty procedures are being performed in progressively younger, obese patients. Hence, maintenance of long term physical function will become very important for quality of life, functional independence and hip prosthesis survival. Presently, there are no reviews of the long term efficacy of total hip arthroplasty on physical function. This review: 1) synopsized available data regarding obesity effects on long term functional outcomes after total hip arthroplasty, and 2) suggested future directions for research.
Methods
A literature search was conducted from 1965 to January of 2011 for studies that evaluated long term functional outcomes at one year or longer after THA in obese (body mass index values ≥30 kg/m2) and non-obese patients (body mass index <30 kg/m2).
Results
Five retrospective studies and 18 prospective studies were identified as those that assessed physical function before surgery out to ≥ one year after total hip arthroplasty. Study sample sizes ranged from 108–18,968 and followed patients from one to twenty years. Total hip arthroplasty confers significant pain reduction and improvement in quality of life irrespective of body mass index. Functional improvement occurred after total hip arthroplasty among all studies, but obese patients generally did not attain the same level of physical function by the follow-up time point.
Discussion
Uncontrolled obesity after total hip arthroplasty is related to worsening of comorbidities and excessive health care costs over the long term. Aggressive and sustainable rehabilitation strategies that include physical exercise, psychosocial components and behavior modification may be highly useful in maximizing and maintaining weight loss after total hip arthroplasty.
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Vincent, Heather K
Horodyski, MaryBeth
Gearen, Peter
Vlasak, Richard
Seay, Amanda N
Conrad, Bryan P
Vincent, Kevin R
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Heather K Vincent et al.; licensee BioMed Central Ltd.
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Journal of Orthopaedic Surgery and Research. 2012 Apr 25;7(1):16
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