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Kinematic and Kinetic Analysis of the Reverse Shoulder Joint

Permanent Link: http://ufdc.ufl.edu/UFE0044298/00001

Material Information

Title: Kinematic and Kinetic Analysis of the Reverse Shoulder Joint an in Vivo Analysis
Physical Description: 1 online resource (40 p.)
Language: english
Creator: Walker, David R
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2012

Subjects

Subjects / Keywords: activation -- arthroplasty -- kinematics -- kinetics -- muscle -- reverse -- shoulder
Mechanical and Aerospace Engineering -- Dissertations, Academic -- UF
Genre: Mechanical Engineering thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Reverse Total shoulder arthroplasty (RTSA) is utilized to restore shoulder function in patients with osteoarthritis and rotator cuff deficiency. The purpose of this study was to assess the behavior of RTSA shoulder subjects as compared to healthy shouldered subjects. Scapulohumeral rhythm (SHR) of patients with RTSA during unloaded shoulder abduction and deltoid muscle activity during active shoulder abduction, flexion and external rotation were measured to give insight into the function of RTSA shoulders compared to normal shoulders. We studied 33 subjects at least 6 months post unilateral reverse total shoulder arthroplasty. Seventeen subjects (11-medial, 6- lateral) performed shoulder abduction (elevation and lowering) during fluoroscopic imaging. SHR was calculated from the slope of the humeral and scapular elevation angles. Subjects then performed both weighted (1.5kg) and un-weighted abduction (coronal plane) and forward flexion (sagittal plane), and un-weighted external rotation. Activation of the anterior, lateral and posterior aspects of the deltoid and upper trapezius muscles were recorded bilaterally using bipolar surface electrodes. Motion capture using passive reflective markers was used to quantify three-dimensional motions of both shoulders. For abduction above 40?, shoulders with RTSA exhibited an average SHR of 1.2:1. There were significant differences in SHR between medial and lateral offset groups of RTSA shoulders (p<<0.05).During abduction, lateral deltoid activity was significantly higher in implanted than in non-implanted shoulders for the medial group. During flexion, the anterior deltoid was significantly more active in the lateral group during weighted and un-weighted flexion. Posterior deltoid was not activated over 40% of MVIC. SHR in RTSA shoulders is significantly different from normal shoulders. Significant differences also occur between RTSA groups (medial/lateral). The muscle recruitment data suggest reverse total shoulder arthroplasty simplifies deltoid muscle activation. We observed higher muscle activation in the portion of the deltoid directly in line with the task, but reduced muscle function in the out-of-line portions of the muscle. This information will be useful to guide refinement in the geometric design of the prosthetic components, surgical alignment of the implants, intraoperative soft-tissue tensioning, and the design of muscle strengthening programs.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by David R Walker.
Thesis: Thesis (M.S.)--University of Florida, 2012.
Local: Adviser: Banks, Scott A.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2012
System ID: UFE0044298:00001

Permanent Link: http://ufdc.ufl.edu/UFE0044298/00001

Material Information

Title: Kinematic and Kinetic Analysis of the Reverse Shoulder Joint an in Vivo Analysis
Physical Description: 1 online resource (40 p.)
Language: english
Creator: Walker, David R
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2012

Subjects

Subjects / Keywords: activation -- arthroplasty -- kinematics -- kinetics -- muscle -- reverse -- shoulder
Mechanical and Aerospace Engineering -- Dissertations, Academic -- UF
Genre: Mechanical Engineering thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Reverse Total shoulder arthroplasty (RTSA) is utilized to restore shoulder function in patients with osteoarthritis and rotator cuff deficiency. The purpose of this study was to assess the behavior of RTSA shoulder subjects as compared to healthy shouldered subjects. Scapulohumeral rhythm (SHR) of patients with RTSA during unloaded shoulder abduction and deltoid muscle activity during active shoulder abduction, flexion and external rotation were measured to give insight into the function of RTSA shoulders compared to normal shoulders. We studied 33 subjects at least 6 months post unilateral reverse total shoulder arthroplasty. Seventeen subjects (11-medial, 6- lateral) performed shoulder abduction (elevation and lowering) during fluoroscopic imaging. SHR was calculated from the slope of the humeral and scapular elevation angles. Subjects then performed both weighted (1.5kg) and un-weighted abduction (coronal plane) and forward flexion (sagittal plane), and un-weighted external rotation. Activation of the anterior, lateral and posterior aspects of the deltoid and upper trapezius muscles were recorded bilaterally using bipolar surface electrodes. Motion capture using passive reflective markers was used to quantify three-dimensional motions of both shoulders. For abduction above 40?, shoulders with RTSA exhibited an average SHR of 1.2:1. There were significant differences in SHR between medial and lateral offset groups of RTSA shoulders (p<<0.05).During abduction, lateral deltoid activity was significantly higher in implanted than in non-implanted shoulders for the medial group. During flexion, the anterior deltoid was significantly more active in the lateral group during weighted and un-weighted flexion. Posterior deltoid was not activated over 40% of MVIC. SHR in RTSA shoulders is significantly different from normal shoulders. Significant differences also occur between RTSA groups (medial/lateral). The muscle recruitment data suggest reverse total shoulder arthroplasty simplifies deltoid muscle activation. We observed higher muscle activation in the portion of the deltoid directly in line with the task, but reduced muscle function in the out-of-line portions of the muscle. This information will be useful to guide refinement in the geometric design of the prosthetic components, surgical alignment of the implants, intraoperative soft-tissue tensioning, and the design of muscle strengthening programs.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by David R Walker.
Thesis: Thesis (M.S.)--University of Florida, 2012.
Local: Adviser: Banks, Scott A.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2012
System ID: UFE0044298:00001


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1 KINEMATIC AND KINETIC ANALYSIS OF THE REVERSE SHOULDER JOINT: AN IN VIVO ANALYSIS By DAVID R WALKER A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2012

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2 2012 David R. Walker

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3 ACKNOWLEDGMENTS I would like to thank first and foremost my Lord Jesus Christ for keeping me and sustaining my strength for this process. It is through his strength that I had the ability to accomplish such a formidable task. I would then like to thank my advisor Dr. Scot t Arthur Banks for all his undying help over the last 4.5 years. He has been instrumental in guiding and developing my skills. It was his ability to trust in my ability to run the studies being presented in thesis that allowed me to persevere and accomplis h this task. I would then like to thank Dr. Thomas Wright for also trusting in my ability to accomplish the task of running these studies. Dr. Wright also served as a mentor in understanding the shoulder anatomy as well as the reverse prosthesis function. I would like to also thank Aimee Struk for her instrumental recruitment and aiding to test all of the subjects. She has been a pleasure to work with and instrumental to getting this studies complete. I would like to thank Dr. Bryan Conrad for all his assis tance and mentorship. His training of use of the motion capture lab was instrumental in the successful completion of the studies presented. I would like to thank Dr. Bo Gao who mentored and was instrumental in the development of the initial analysis tools for both kinematic and EMG analysis. I would like to thank Lyneesha Sweeney, Courtney Cox, Mpho Sello, and Adori for their hard work in shape matching images for kinematic analysis. I would like to thank Ms. Jennifer Jones for her instrumental help in digi tizing motion data captured by the motion capture system. I would like to thank Ms. Eve Culbreth for her moral support through this time. Lastly I would like to thank my mother (Ms. Audrey Fisher) for her encouraging words and support through this whole p rocess.

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4 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ ............... 3 LIST OF FIGURES ................................ ................................ ................................ ......................... 5 ABSTRACT ................................ ................................ ................................ ................................ ..... 6 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .................... 8 Shoulder Anatomy ................................ ................................ ................................ .................... 8 Shoulder Joint Injuries ................................ ................................ ................................ .............. 8 Reverse Total Shoulder Arthroplasty ................................ ................................ ....................... 8 Scapulohumeral Rhyth m (SHR) ................................ ................................ ............................... 9 Muscle Activation and Function ................................ ................................ ............................. 10 2 SCAPULOHUMERAL RHYTHM OF REVERSE TOTAL SHOULDER ARTHROPLASTIES DURING NON WEIGHTED SHOULDER ABDUCTION .............. 16 Testing Protocol ................................ ................................ ................................ ...................... 16 Im age Acquisition and 3D Modeling ................................ ................................ ..................... 17 Model Image Registration ................................ ................................ ................................ ...... 17 Data Processing ................................ ................................ ................................ ...................... 18 Statistical Analysis ................................ ................................ ................................ .................. 18 3 REVERSE TOTAL SHOULDER ARTHROPLASTY SIMPLIFIES MUSCLE FUNCTION DURING ABDUCTION, FLEXION AND EXTERNAL ROTATION. .......... 24 Testing Protocol ................................ ................................ ................................ ...................... 25 Apparatus Set Up ................................ ................................ ................................ .................... 25 Lateral Delt oid ................................ ................................ ................................ ........................ 26 Anterior Del toid ................................ ................................ ................................ ...................... 26 Posterior Deltoid ................................ ................................ ................................ ..................... 27 General Observations ................................ ................................ ................................ .............. 27 4 CONCLU SION ................................ ................................ ................................ ....................... 35 Abduction ................................ ................................ ................................ ............................... 35 Flexion ................................ ................................ ................................ ................................ .... 36 LIST OF REFERENCES ................................ ................................ ................................ ............... 37 BIOGRAPHICAL SKETCH ................................ ................................ ................................ ......... 40

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5 LIST OF FIGURES Figure page 1 1 The human shoulder girdle consists of the humerus, scapula and clavicle ....................... 11 1 2 The shoulder musculature is multilayered and complex. ................................ ................... 12 1 3 A typical rotator cuff tear. From southwest orthopaedics medical center:. ....................... 13 1 4 Implanted reve rse shoulder prostheses can change significantly the medial/lateral location of the shoulder center of rotation. ................................ ................................ ........ 14 1 5 Rotator cuff deficient shoulders often lack sufficient stability to elevate without superior translation and impingement with an anatomic total shoulder arthroplasty ........ 15 2 1 Protocol of weighted abduction during fluoroscopy.Photo courtesy of David Walker at the Orthopaedic Sports and Medical Institute (OSMI) ................................ .................. 20 2 2 Humeral and scapular coordinate systems and degrees of freedom. ................................ 21 2 3 Reverse implant designs A. medial type implant B. neutral type implant C. Lateral type implant ................................ ................................ ................................ ....................... 22 2 4 Scapulahumeral rhythm of RTSA (medial vs. lateral) vs. normal population ................... 23 3 1 Surface electromyography placement ................................ ................................ ................ 31 3 2 Muscle activation of the implanted side lateral deltoid during un weighted abduction. ... 31 3 3 Muscle activation of the non implanted side lateral deltoid during un weighted abduction ................................ ................................ ................................ ............................ 32 3 4 Muscle activation of the implanted anterior deltoid during weighted flexion ................... 32 3 5 Muscle activation of the non implanted anterior deltoid during weighted flexion ........... 33 3 6 Muscle activation of the implanted posterior deltoid during un weighted external rotation ................................ ................................ ................................ ............................... 33 3 7 Muscle activation of the implanted posterior deltoid during weighted flexion ................. 34 3 8 Muscle activation of the non implanted posterior deltoid during un weighted abduction ................................ ................................ ................................ ............................ 34

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6 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requir eme nts for the Degree of Master of Science KINEMAT IC AND KINETIC ANALYSIS OF THE REVERSE SHOULDER JOINT: AN IN VIVO ANALYSIS By D avid R. Walker May 2012 Chair: Scott Arthur Banks Major: Mechanical Engineering Reverse Total shoulder arthroplasty (RTSA) is utilized to restore shoulder function in patien ts with osteoarthritis and rotator cuff deficiency. The purpose of this study was to assess the behavior of RTSA shoulder subjects as compared to healthy shouldered subjects Scapulohumeral rhythm (SHR) of patients with RTSA during unloaded shoulder abduc tion and deltoid muscle activity during active shoulder abduction, flexion and externa l rotation were measured to give insight into the function of RTSA shoulders compared to normal shoulders. We studied 33 subjects at least 6 months post unilateral reverse total shoulder arthroplasty. Seventeen subjects (11 medial, 6 lateral) performed shoulder abduction (elevation and lowering) during fluoroscopic imaging. SHR was calculated from the slope of the humeral and scapul ar elevation angles Subjects then performed both weighted (1.5kg) and un weighted abduction ( coronal plane ) and forward flexion ( sagittal plane ) and un weighted external rotation. A ctivation of the anterior, lateral and posterior aspects of the deltoid a nd upper trapezius muscles were recorded bilaterally using bipolar surface electrodes. Motion capture using passive reflective markers was used to quantify three dimensional motions of both shoulders.

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7 For abduction above 40 shoulders with RTSA exhibited an average SHR of 1.2:1. There were significant difference s in SHR between medial and lateral offset groups of RTSA shoulders (p< <0 .05). Durin g abduction, lateral deltoid activity was significantly higher in implanted than in non implanted shoulders for the medial group. During flexion, the anterior deltoid was significantly mor e active in the lateral group during weighted and un weighted flexion. Posterior deltoid was not activated over 40% of MVIC. SHR in RTSA shoulders is significantly different from n ormal shoulders. Significant differences also occur between RTSA groups (medial/lateral) The muscle recruitment data suggest reverse total shoulder arthroplasty simplifies deltoid muscle activation. We observed higher muscle activation in the portion of t he deltoid directly in line with the task, but reduced muscle function in the out of line portions of the muscle This information will be useful to guide refinement in the geometric design of the prosthetic components, surgical alignment of the implants, intraoperative soft tissue tensioning, and the design of muscle strengthening programs.

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8 CHAPTER 1 INTRODUCTION Shoulder Anatomy The shoulder jo int is comprised of three bones, the humerus, the scapula and the clavicle (Figure 1 1) [20] The shoulder is co ntrolled by a variety of muscles (Figure 1 2) [20] The rotator cuff muscles the trapezius and the deltoid serve to lift and stabilize the arm. The joint achieves great mobility under coordinated control of these muscles. An irreparable tear of the rotator cuff muscles may functionally immobilize the shoulder There are several different disorders that lead to immobilization of the shoulder. Shoulder Joint Injuries Shoulder joint related problems are a common reason for visits to the Orthopaedic s urgeon. In 2003 14 million people in the United States visited a doctor for a shoulder related i njury [27 ]. These people suffered from a variety of disorders such as rotator cuff arthropathy (Figure 1 3) frozen shoulder, and shoulder impingement syndrome [27] Irreparable tears of the rotator cuff muscles (Teres minor, supraspinatus, infraspinatus, and subscapularis) will cause the development of osteoarthritis (Figure1 3) and impairment of motion of the shoulder [ref] In the event of an irreparable rot ator cuff (Figure 1 3) the Reverse Total Shoulder Arth roplasty (RTSA) is an increasingly popular option to restore mobility in the shoulder Reverse Total Shoulder Arthroplasty The Reverse Total Shoulder Arthroplasty (RTSA) Paul Grammont who developed the principles lead ing to successful reverse and total sho ulder prostheses [21]. A reverse prosthesis is comprised of a glenosphere, a humeral stem, and a humeral cup (Figure 1 4). The rev erse prosthesis possesses several potential advantages. In a normal shoulder with an irreparable r otator cuff tear, patients often experience pain and

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9 dislocation of the humeral head. RTSA obviates the need for rotator cuff muscles by fixing the center of rotation (COR) of the humerus relative to the scapula. This allows for stabili zation of the COR without need for dynamic muscular stabilization of the joint The implant defined COR also allows for manipulation of the deltoid moment arm. RTSA can alleviat e pain while restoring motion to shoulders with irreparable rotator cuff injuries or failed total shoulder replacements (Figure 1 5) The optimal amount of lateral offset in RTSA remains the subject of current study and debate [refs]. Three designs of RTS A were available to study for this thesis, with each adopting a different philosophy for how far laterally the COR should be placed (medial, neutral and lateral, Figure 1 4) [21, 25]. Improper placement of the COR can lead to possible implant failure by g lenoid loosening, and impingement syndrome Therefore, information on reverse shoulder joint behavior with reference to normal shoulders is vital to identify ideal placement of the COR and minimize implant failure The measurement of motion and muscle fun ction in RTSA shoulders is the primary motivation for the studies that comprise C hapters 2 and 3. The measurement of motion of the humerus and scapula will be used to calculate a parameter known as the scapulohumeral rhythm (SHR) Scapulohumeral Rhythm (SHR ) The coordinated motion of the humerus and scapula has been defined as a ratio between how each of the bodies move, hence the scapulohumeral rhythm (SHR). SHR was first reported to be a constant 2:1 (humerus : scapula) ratio by Inman et al for normal healt hy subjects [27] Many researchers have since measured SHR in normal and pathological shoulders [27 29] To date, there has been no report of SHR for RTSA patients. Alterations in the position and movement of the scapula, called scapular dyskinesia [28 29] change the SHR and likely

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10 manifest in various shoulder disorders, such as rotator cuff tears, impingement syndrome, frozen shoulder, osteoarthritis, throwing injuries and instability [22] It is vital to know the SHR of the RTSA popu lation in determining if RTSA SHR differs from normal shoulders and to assess possible points of failure for the implant. Calculating SHR of RTSA subjects during shoulder abduction will help assess how the RTSA shoulder functions with respect to a normal shoulder. Muscle Act ivation a nd Function Muscles are the actuators of the shoulder joint. They produce tension that is applied to the bone s via tendon s to drive motion In RTSA patients the primary muscles that perf orm lifting of the arm are the d eltoi ds and the upper trapezius (Figure 1 2) [21,24] How these muscles are recruit ed is vital to understand ing the function of the RTSA shoul der. It is likely that c hange s in RTSA geometry directly affect the function of these muscles. Measurements of muscle activity during abduction flexion and exte rnal rotation will be presented in Chapter 3 By measuring muscle activity during t hese activities, a model of how muscle recruit ment varies with different RTSA designs can be developed These measurements can be used to assess ideal placement of the COR to optimize function in RTSA shoulders.

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11 Figure 1 1. The human shoulder girdle consists of the humerus, scapula and clavicle ( From: between mob 2129 )

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12 Figure 1 2. The shoulder m usculature is multilayered and complex For RTSA shoulders, the muscles of greatest functional importance are the deltoid and trapezius. Sagittal (top) and posterior coronal views (bottom) (from : H.E.J. Veeger and F.C.T. van derHelm, of Biomechanics 40 (2007) 2119 2129 )

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13 Figure 1 3. A typical rotator cuff tear. From southwest orthopaedics medical center: www.southwest ortho.com/images/sports/shoulder rotator cuff.jpg

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14 Figure 1 4. Implanted r everse shoulder prosthes e s can change significantly the medial/lateral location of the shoulder center of rotation. From http://www.jaaos.org/content/19/7/439/F4.expansion

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15 Figure 1 5. Rotator cuff deficient shoulders often lack sufficient stability to elevate without superior translation and impingement with an anatomic total shoulder art hroplasty (A). Patients with reverse total shoulder arthroplasty (B) often can elevate their geometrically stable shoulder without superior translation and impingement (C). From http://www.shouldersurgeon.com/shoulder_replacement_surgery/

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16 CHAPTER 2 SCAPULOHUMERAL RHYTHM OF REVERSE TOTAL SHOULDER ARTHROPLASTIES DURING NON WEIGHTED SHOULDER ABDUCTION Reverse total shoulder arthroplasty (RTSA) is an effective treatment option for patients with symptomatic glenohumeral arthritis and a deficient rotator cuff. RTSA has been reported to produce early satisfactory clinical outcomes in terms of pain relief and restoration of active forward flexion and abduction [21, 23, and 24 ]. However, deltoid tensioning and potential instability, humeral fixation, glenosph ere fixation, scapular notching and polyethylene wear are currently unsolved challenges that may lead to a significant decrease in the functional outcomes and increase the risk of RTSA failure [24] There is currently little known about shoulder function after R T SA or if differences in surgical technique or implant desig n affect shoulder performance [21, 23, 24 ]. A better understanding of the motion of the shoulder after RTSA is critical to understand how shoulders with RTSA function and how to address the se challenges and improve functional outcomes and longevity. The purpose of this study was to quantify scapulohumeral rhythm (SHR) in p atients with RTSA during unloaded shoulder abduction. Testing Protocol Seventeen subjects gave informed written consent to participate in an Institutional Review Board (IRB) approved protocol. These subjects had uni or bi lateral RTSA and performed shoulder abduction (elevation and lowering) with and w ithout a handheld 1.36 kg we ight (Figure 2 1) Subjects received one of three RTSA designs (Aequalis Tornier, Inc., Edina, MN; Equinoxe Reverse Shoulder, Exactech Inc., Gainesville, FL; RSP DJO Surgical, Austin TX). The Aequalis (n=6) and Equinoxe (n=5) shoulders composed the Medial Group, while the RSP shoulders (n=6) composed the Lateral Group based upon the lateral offset of the glenosphere center of rotation.

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17 A group of young healthy shoulders examined using the same protocol and measurement methods served as a Contro l Group [33 Matsuki et al]. Image A cquisition and 3D M odeling Fluoroscopic images of the implanted shoulder for each subject were captured during non weighted abduction (recorded at 7.5 Hz ) using a C arm fluoroscopy machine (give model name and maker, city ) The subject stood parallel to the plane of the image intensifier Elevation and lowering in the frontal plane were performed, at approximately eight sec onds per cycle, with the elbow fully extended and the arm extern ally rotated Subjects were allowed t o move their arms naturally, their bodies were not constrained, and the speed of motion was not strictly controlled. Subjects performed the activity while it was demonstrated by the testing staff. Three dimensional implant surface models were acquired fro m the manufacturers of all implant designs. The models were oriented and translated to establish consistent component origins and alignment (Figure 2 1). The Y axis was parallel to the humeral shaft, and Z axis was defined as a line through the intertuber cular groov X axis was horizontal pointed medially toward the center of the body and Y and Z axes was pointed superiorly and anteriorly, respectively (Figure 2 2 ). Model I mage R egistration The 3D positio n and orientation of the humeral and the scapula r components were determined using model image registration techniques ( Figure 2 3 ) [26] The implant model was projected onto the distortion corrected fluoroscopic image, and its three dimensional pose was iterati vely adjusted to match its silhouette with the silhouette of the fluoroscopic image (Figure 2 3)

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18 Data P rocessing The kinematics of the humerus and the scapula components of the implant relative to the x ray coordinate system were determined using Cardan angles [30]. Elevation of the humeral component was defined as rotation about the Z axis. Motion of the scapula r component was defined as anterior posterior tilt about the X axis, internal external rotation about the Y axis, and upward downward rotation ab out the Z axis (Figure 2 2 ). Scapular elevation was plotted as a function of humeral elevation, and a best fit polynomial regression curve was used to interpolate scapular elevation values in 15 increments of the humeral elevation angle [31]. SHR was cal culated from arm at side to maximum elevation positions using the expression SHR = component is the increment in scapular component upward rotation angle [27] SHR was computed at 15 increment s polynomial regression line using scapular upward rotation as the independent value and humeral elevation angle as the dependent value. Then, SHR w as calculated as 1 1. Statistical A nalysis T wo way repeated measures analysis of variance (ANOVA) was used to comp are the incremental data of scapular angles and SHR between between Medial and Lateral RTSA groups, and between RTSAs and Controls.T he level of significance for all comparisons was set at p< 0 .05. wise post hoc comparisons. There was a significant difference between the RTSA group and the normal group SHR (p< 0.05, p=0.0000 8). For abduction above 40 shoulders with RTSA exhibited an average SHR

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19 of 1.2:1 (Figure 2 4 ) There was significant difference in SHR between medial and lateral offset groups of RTSA shoulders (p=0.002341 ). SHR was highly variable for abduction less tha n 40 with SHR ranging from a low of 1 to greater than 10 (Figures.2 4) At arm elevation angles less than 40 SHR in RTSA shoulders is highl y variable and the mean SHR (Figures. 2 4,) for RTSA appears higher than the SHR for normal shoulders (Figures. 2 4 ). At higher elevation angles SHR in shoulders with RTSA (1 1.4 ) is much more consistent and is lower than SHR in normal shoulders (2 4). At higher elevations the scapula rotates a lot more in the reverse shoulder population (Figures. 2 4,) Medial and lateral groups within the RTSA population have a significant difference in SHR (p=0.0002341). It can be observed that rotator cuff deficient, art hritic shoulders treated with R TSA do not move like healthy young shoulders. Previous studies have looked at n ormal shoulder SHR [9, 27 29]. This study purposed to calculate the SHR for RTSA patients. Significant differences were found between the SHR for RTSA population as compared to the normal population. There were significant differences found in the SHR betw een medial and lateral RTSA shoulder groups. This insight shows that the RTSA SHR is different from normal shoulders and it is also different depending on the RTSA design (medial/lateral). Comparison of RTSA groups (medial/lateral) to normal shoulders may give insight to which RTSA design restores more of a normal function to the shoulder.

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20 Figure 2 1. Protocol of weighted abduction during fluoroscopy. Photo courtesy of David Walker at the Orthopaedic Sports and Medical Institute (OSMI)

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21 Figure 2 2. Humeral and scapular coordinate systems and degrees of freedom From citation 27

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22 Figure 2 3. Reverse implant designs A. medial type implant B. neutral type implant C. Lateral type implant From exac.com, tornier.com, encore.com

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23 F igure 2 4 Scapulahumeral rhythm of RTSA (medial vs. lateral) vs. n ormal population

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24 CHAPTER 3 REVERSE TOTAL SHOULDER ARTHROPLASTY SIMPLIFIES MUSCLE FUNCTION DURING ABDUCTION, FLEXION AND EXTERNAL ROTATION Reverse total shoulder arthroplasty (RTSA) is an effective treatment option for patients with symptomatic glenohumeral arthritis and a deficient rotator cuff. RTSA has been reported to produce early satisfactory clinical outcomes in terms of pain relief and restoration of active forward fle xion and abdu ction [1 ]. However, deltoid tensioning and potential instability, humeral fixation, glenosphere fixation, scapular notching and polyethylene wear are currently unsolved challenges that may lead to a significant decrease in the functional outcomes and increase the risk of RTSA failure [24] A better understanding of muscle activity after RTSA is cri tical to understand how shoulders with RTSA function and how to address these challenges and improve functional outcomes and longevity. Most RTSA research efforts have focused on improving the design and biomechanics of reverse prostheses. Few studies have focused on the deltoid, which becomes the primary mover in the rotator cuff deficient shoulder and RTSA. We currently lack a fundamental understanding how deltoid tension and activity relates to functional outcomes such as range of motion (ROM), arm stren gth and functional scores with RTSA. Insufficient deltoid tensioning may lead to prosthetic instability, whereas excessive deltoid tension may result in acromial fractures [4]. Deltoid tensioning is thought to directly affect the activation pattern and act ive force generating ability of the muscle [4 6], such that active ROM and shoulder function depend on the interplay between RTSA geometry and deltoid length and tension. In the healthy and rotator cuff deficient shoulder, muscle tension is required to dyn amically stabilize the glenohumeral joint and to move the arm. RTSA provides definitive geometric stability to the replaced shoulder so that muscle tension is not required to stabilize the glenohumeral joint. Thus, we might expect muscle fibers in the most mechanically advantageous

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25 locations to be preferentially recruited to perform functional tasks, while collateral and antagonist muscle activity is decreased compared to non RTSA shoulders. This hypothesis is the converse of phenomena observed in the knee where joint instability results in increased antagonist muscle activity as a means to dynamically stabilize the joint [7]. The purpose of this study was to determine shoul der muscle recruitment i n patients with RTSA. We measured deltoid and upper trapezius muscle activity in the RTSA and non involved contralateral shoulders of subjects during both weighted and un weighted shoulder abduction and flexion, and un weighted external rotation. Testing Protocol 50 subjects (33 RTSA, 17 healthy ) between 60 85 years of age gave written consent to participate in this IRB approved study. Patients were an average of 37 months post unilateral RTSA (range 12 63 months). Patients received prosthes e s with a medial or lateral center of rotation : The Medial Group consisted of 17 shoulders with an Aequalis implant (Tornier Inc., Edina, MN) or an Equinoxe impla nt (Exactech, Gainesville, FL), and the Lateral Group consisted of 16 shoulders with a Reverse implant (DJO surgical, Austin TX) (Figure 2 3). recorded during weighted and un weighted abduction, weighted and un weighted flexion, and un weighted external rotation. Motions were performed so that one cycle required approximately 15 seconds. Weighted trials utilized a 1.5kg hand held weight. Each su bject was tested bilaterally. Subjects rested for 2 minutes between activities to minimize the effects of fatigue. Apparatus Set Up A twelve camera motion capture system was used to record the motions of fifteen skin mounted retro reflective markers at 6 0Hz ( Fig ure 3 1) [8 9] Eight channels of s kin surface e lectromyography (EMG) w ere collected simultaneously at 1200 Hz using bipolar electrodes

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26 placed bilaterally on the anterior, lateral, and posterior aspects of the deltoid and on the upper trapezius ( Figure 3 1, Telemyo 2400,Nora xon USA Inc. Scottsdale, AZ) [10 ]. Maximal voluntary isometric contraction (MVIC) data and maximal activation during each functional activity performed were used to normalize the EMG signals [11 ]. A hand held dynamometer was us ed to measure the maximum force generated at the wrist joint during MVIC trials. Reflective marker kinematics were determined using standard software (EvaRT, Motion Analysis Corporation, Santa Rosa, CA) and filtered using a fourth order, zero phase shift, low pass Butterworth filter with a 12 Hz cutoff frequency. A custom program was used to compute shoulder abduction, flexion, and external rotation angles using an abduction flexion external rotation sequence [30] EMG data were mean filtered [10 ] and fitt ed spline curves were used to determine the EMG signal magnitude at specific arm angles. Comparisons between the RTSA and contralateral shoulders were performed using t wo way repeated measures ANOVA with t he level of significance chosen to be 0.05. Honestly Significant Difference was used to perform pair wise post hoc comparisons. Lateral Deltoid Activation of the lateral deltoid was significantly higher in the Medial Group of RTSA shoulder s than in the ir contralateral shoulder during weighted and un weighted abduct ion throughout the entire cycle (Figures 3 2, 3 3, middle graph). The Lateral Group of RTSA shoulders showed significantly higher activation of the lateral deltoid muscle in the first 70 of humeral elevation (Figures 3 2, 3 3, lateral gr aph, p<<0.05). After 70 the non implanted side had a higher activation for the lateral deltoid muscle (Figure 13 14, top graph, p<<0.05). Anterior Deltoid Activation of the anterior deltoid was significantly higher in the implanted shoulder of Lateral Gr oup of RTSA shoulders than in the ir contralateral shoulder s during weighted and un

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27 weighted flexion throughout the entire cycle (Figures 3 4, 3 5, top graph). The Medial Group of shoulders showed significantly higher activation of the lateral deltoid muscl e in the first 50 of humeral elevation during flexion (Figures 3 4,3 5, middle graph, p<<0.05). After 50, the contralateral shoulders showed higher lateral deltoid activation (Figures 3 4, 3 5, bottom top, p<<0.05). Posterior Deltoid Maximum posterior deltoid activity of 18% MVIC was observed during external rotation in RTSA shoulders and posterior deltoid activity in all activities averaged less than 40% of M VIC for both RTSA and uninvolved shoulders (Figures 3 6 3 7 and 3 8 ) General Obse rvations Weighted trials showed significantly higher muscle activation t han un weighted trials (Figures 3 4, 3 5 ). RTSA shoulders did not elevate as far as contralateral should ers during weighted trials (Figures 3 4 ). During weighted trials, RTSA implanted shoulders showed significantly higher activation of muscle fibers acting in line with the motion, e.g. lateral deltoid for abduction and anterior deltoid for flexion ( Figures 3 2, 3 4 ). Anterior and posterior deltoid activation in RTSA shoulders were comp arable or lower than in contralateral shoulders during weighted abduction. Posterior deltoid was not highly active during unresisted internal/external rotator Deltoid muscle function is a critical determinant of shoul der function following RTSA. I t r emains difficult to determine optimal deltoid tensioning during reverse shoulder surgery, and there is little objective information about how the deltoid functions in RTSA patients. The purpose of this study was to quantify deltoid and upper trapezius musc le activity in shoulders with RTSA. We found muscle function in the shoulder with RTSA is significantly different from the normal shoulder. RTSA shoulder deltoid activity is higher for fibers in line with the motion,

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28 and lower for adjacent parts of the mus cle (Figures 3 2, 3 4 ). ) As expected, muscle activity increased during weighted trials in both RTSA and contralateral shoulders (Figures 3 4, 3 5 ). ) [12] Th e results suggest simplified muscle coordination post RTSA, where muscles act to move the arm but play less of a joint stabilizing role. This study includes 33 patients with unilateral RTSA. All subjects received RTSA devices with medial and lateral centers of rotation, and so should be representative of that patient group. alateral shoulder for comparison, but their contralateral shoulder muscle activity may not be representative of healthy or young shoulders. We were limited to eight channels of EMG, four channels bilaterally, so it was not possible to record muscle activit y for teres minor or other important shoulder muscles. We attempted to minimize experimental variability by (1) having a single examiner prepare and place the EMG electrodes for all subjects; (2) coaching subjects on how to perform the MVIC trials to get t he best possible activation levels for normalization; and (3) saving for analysis only trials where the subject maintained the correct upright posture. Our primary finding is deltoid activation is strongly related to activity, such that deltoid fibers dir ectly causing motion are active while adjacent fibers are relatively quiet. Thus, the lateral deltoid was hig hly active for abduction (Fig. 3 2 ) while the anterior deltoid was h ighly active for flexion (Fig. 3 4 ). The posterior deltoid was minimally active during th e three motions studied (Figure 3 6, 3 7, 3 8 ). The posterior deltoid showed only 20% activation during unresisted external rotation which does not support the literature [13] (Figure 3 7) This might change dramatically for external rotation ag ainst resistance, with the posterior deltoid MVIC trials as an example.

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29 In healthy shoulders the primary arm abductors are the deltoid and upper trapezius [14 17]. Increased activation of the deltoid muscles has been found in patients with impingement and /or rotator cuff deficiency [18 19]. Increased deltoid activity in cuff deficient shoulders leads to instability and upward humeral migration. Our secondary finding was that deltoid fibers not in line with motion were significantly less active in RTSA shou lders than in the contralateral shoulders (Figure 3 7) During flexion RTSA shoulders showed high activity for anterior deltoid fibers and lower activity in lateral and pos terior fibers. During abduction medial RTSA shoulders showed high lateral deltoid activity and lower activity in the anterior and posterior fibers. Lateral RTSA shoulders showed this pattern for all elevation angles during abduction. These findings suggest generalized deltoid activity in contra lateral shoulders provides glenohumeral stability, while that function is less required in the intrinsically stable RTSA shoulders. These findings provide an interesting counterpoint to knee joint function, where antagonist muscle cocontraction increases a s a stabilizing mechanism for knee instability after ACL tears [7]. For both abduction and flexion motions, deltoid activity reaches a plateau mid motion with greater abduction or flexion. These patterns of muscle activation suggest an increasing contri bution of scapular rotation to overall motion at higher abduction/flexion angles, or a decreasing scapulohumeral rhythm. The SHR results in Chapter 2 support this assertion. Deltoid fibers directly in line with the motion work increasingly harder at low an d middle angles of motion, and then maintain a high level of activation at greater degrees of elevation. This muscle activity coincides with greater glenohumeral motion in the RTSA patients at low angles with increasing contribution of scapular thoracic mo tion above 40 degrees as the upper trapezius becomes more active.

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30 We conclude that deltoid function in shoulders with RTSA is not normal. Deltoid function appears to be greatly simplified, where the major task is arm motion w ith most shoulder stability pr ovided by the implant. Opposing heads of the deltoid no longer need to work in an eccentric fashion to balance the glenohumeral joint. Lateral deltoid fibers are active for abduction and relatively quiet during flexion, while anterior fibers are active for flexion and relatively quiet for abduction. Medial and Lateral Groups of RTSA shoulders exhibit statistically distinct muscle activation patterns, which will be more fully explored in future work. Contrary to popular opinion we found little role for the p osterior deltoid (only 20% activation) in unresisted exter nal rotation in RTSA patients (Figure 3 6) The posterior deltoid was also quiet for abduction and flexion (Figures.3 7, 3 8) These observations of muscle function in RTSA shoulders improve our un derstanding of joint function in rotator cuff deficient replaced shoulders. Specific deltoid fibers in line with the desired motion act as the primary mover of the arm at low and mid angles of elevation, and this has major implications for rehabilitation, surgical technique and implant design. Based on our findings, rehabilitation might productively focus on the anterior and lateral deltoid at low and mid angles of flexion and abduction, respectively to opti mize function in patients with medial ized and lat eralized center of rotation RTSA. There appears to be little value in a strengthening program directed at the posterior deltoid.

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31 Figure 3 1. Surface e lectromyography placement Photo provided by David R Walker at the orthopaedic sport and medical institute. Figure 3 2. Muscle activation of the implanted side lateral deltoid during un weighted abduction Provided by R software

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32 Figure 3 3. Muscle activation of the non implanted side lateral deltoid during un weighted abduction Figure 3 4. Muscle activation of the implanted anterior deltoid during weighted flexion

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33 Figure 3 5. Muscle activation of the non implanted anterior deltoi d during weighted flexion Figure 3 6. Muscle activation of the implanted posterior deltoid during un weighted external rotation

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34 Figure 3 7. Muscle activation of the implanted posterior deltoid during weighted flexion Figure 3 8. Muscle activation of the non implanted posterior deltoid during un weighted abduction

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35 CHAPTER 4 CONCLUSION Understanding the function of the Reverse Total shoulder Arthroplasty (RTSA) during motion is critical to the design of preclinical plans for the plac ement of the implant. The studies scapulohumeral kinematics and muscle function In Chapter 2 it was found that SHR at low abduction angles in both healthy and RT SA shoulders is highly variable SHR in RTSA shoulders decreases dramatically with abduction, such that mostly scapular elevation is observed at the extreme of abduction. Rotator cuff deficient arthritic shoulders treated with RTSA do not move like healthy young shoulders (Figure 2 4, 2 5, 2 6) Further, Medial and Lateral RTSA populations had significantly different SHR (p=0.0002341). In Chapter 3 it was found that the lat eral deltoid functioned as the primary abductor (Figure 13 14) of the arm and the anterior deltoid functioned as the primary flexor of the arm (Figures 3 4, 3 5). Posterior deltoid activity in all activities averaged less than 40% of MVIC (Figures 3 6, 3 7 3 8). It was seen that there was a significant difference in activation between the Medial and Lateral Groups of the RTSA population. Abduction For abduction the Lateral RTSA Group had higher lateral deltoid activity in the implanted shoulder for early abduction. Beyond 70 elevation, the contralateral shoulders showed higher lateral deltoid activation than the implanted Lateral Group shoulders. Conversely the Medial Group did not show this behavior; the implanted side displayed a higher activation for t he lateral deltoid for all degrees of elevation than the non implanted side.

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36 Flexion For flexion the Medial Group had higher anterior deltoid activity in the implanted side for early angles of flexion. Above 50 degrees elevation, anterior deltoid activat ion for the Medial Group was higher in the contralateral shoulders than the implanted shoulders. Conversely, the Lateral Group did not show this behavior; the implanted shoulders displayed higher anterior deltoid activation for all degrees of elevation com pared to the non implanted shoulders. This muscle activation pattern is also seen in weighted and un weighted trials of flexion in the anterior deltoid (AD: p<0.05). The findings on shoulder muscle activation with and without RTSA provide context for asses sing how geometric changes in implant design affect shoulder motion and muscle recruitment. It was found that the muscle function and kinematics of the RTSA are significantly different from normal shoulders. These insights may lead to the development of pr eclinical plans for placement of the implant, improved implant design, and modification of rehabilitative strategies to improve outcomes and optimize quality of life for patients who undergo RTSA.

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37 LIST OF REFERENCES 1. Rittm eister M and Kerschbaumer F. Grammont reverse total shoulder arthroplasty in patients with rheumatoid arthritis and nonreconstructible rotator cuff lesions. J Shoulder Elbow Surg 2001; 10: 17 22. 2. Boileau P, Watkinson DJ, Hatzidakis AM and Balg F. Grammont reverse prosthesis: design, rationale, and biomechanics. J Shoulder Elbow Surg 2005; 14: 147S 61S. 3. Boileau P, Watkinson DJ, Hatzidakis AM and Hovorka I. Neer Award 2005: The Grammont reverse shoulder prosthesis: results in cuff tear arthritis, fracture seq uelae, and revision arthroplastry. J Should Elbow Surg 2006; 15: 527 540. 4. Harman, M; Frankle, M; Vasey, B; Banks, S: Initial glenoid component fixation in "reverse" total shoulder arthroplasty: a biomechanical evaluation. J Shoulder Elbow Surg, 14(1S):162 S 167S, 2005 5. De Wilde LF, Audenaert EA and Berghs BM. Shoulder prostheses treating cuff tear arthropathy: a comparative biomechanical study. J Ortho Res 2004; 22: 1222 1230. 6. Lam, F; Bhatia, DN; Mostofi, SB; van Rooyen, K;de Beer, JF. Biomechanical consider ations of the normal and rotator cuff deficient shoulders and the reverse shoulder prosthesis.Orthopeadics. February 2007;21:40 46 7. T. Hortobagyi, L. Westerkamp, S. Beam, J. Moody, J. Garry, D. Holbert, and P. DeVita Clinical Biomechanics vol. 20, Jan. 2005, pp. 97 104. 8. Illyes, A; Kiss M.R. Shoulder muscle activity during pushing, pulling, elevation and overhead throw. Journal of E lectromyography and Kinesiology.2004; 15:282 289. 9. Kon Y, Nishinaka N, Gamada K, Tsutsui H, Banks SA: The influence of hand held weight on the scapulohumeral rhythm. J Shoulder Elbow Surg, 2008, in press. 10. Cram JR, Kasman GS, Holtz J. Introduction to surfac e electromyography. Gaithersburg (MD): Aspen Publishers; 1998. 11. Boettcher, CE; Ginn, KA; Cathers, I.Standard Maximum Isometric Voluntary Contraction Tests for Normalizing Shoulder Muscle EMG. Journal of Orthopedic research. Dec 2008;26:1591 1597 12. Uhl, TL;Car ver, TJ; Mattacola, CG; Mair, SD; Nitz, AJ. Shoulder musculature activation during upper extremity weight bearing Exercise. Journal of Orthopaedics & sports physical therapy. march 2003;33:109 117

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38 13. Reinold, MM; Wilk, KE; Fleisig, GS; Zheng, N; Barrentine, S W;Chmielewski, T;Cody, RC ;Jameson, CG; Andrews, JR. Electromyographic analysis of the rotator cuff and deltoid musculature during common shoulder external rotation exercises. Journal of orhtopaedics& sports physical therapy. July 2004;34:385 394 14. Madeleine P; Farina, D; Merletti, R;Arendt Nielsen, L. Upper trapezius muscle mechanomyographic and electromyographic activity in humans during low force fatiguing and non fatiguing contractions. European Journal of Applied Physiology. Aug 2002;87:327 336 15. Ekstrom RA; Donatelli, RA; Soderberg, GL. Surface electromyographic analysis of exercises for the trapezius and serratus anterior muscles. Journal of Orthopaedic & sports Physical therapy. May 2003;33:247 258 16. Farina, D; Madeleine, P; Graven Nielsen, T; Merletti, R; Arendt Neilsen, L. Standardising surface electromyogram recordings for assessment of activity and fatigue in the human upper trapezius muscle. European Journal of Applied Physiology. April 2002;86:468 478 17. Ekstrom, RA; Soderberg, GL; Donatelli, RA. Norm alization procedures using maximum voluntary isometric contractions for the serratus anterior and trapezius muscles during surface EMG analysis. Journal of Electromyography and Kinesiology.August 2005;15:418 428 18. Phadke, V; Camargo, PR; Ludewig, PM. Scapula r and rotator cuff muscle activity during arm elevation: A review of normal function and alterations with shoulder impingement. Revista Brasileira de Fisioterapia. 2009;13:1 9 19. Steenbrink, F; Meskers, G.M.C.; Nelissen, G.H.H. R.; deGroot ,H. J. The relation between increased deltoid activation and adductor muscle activation due to glenohumeral cuff tears. Journal of Biomechanics. 2010;43: 2049 2054 20. Ebraheim NA, Xu R, Haman SP, Miedler JD, Yeasting RA. Quantitative anatomy of the scapula. Am J Orthop 2000;29: 287 92. 21. Sirveaux F, Favard L, Oudet D, Huguet D, Walch G and Mole D. Grammont inverted total shoulder arthroplasty in the treatment of glenohumeral osteoarthritis with massive rupture of the cuff. Results of a multicentre study of 80 shoulders. J Bone Join t Surg Br 2004; 86:388 95 22. United States Bone and Joint Decade: The Burden of Musculoskeletal Diseases in the United States. Rosemont, IL: American Academy of Orthopaedic Surgeons; 2008. 23. Frankle M, Siegal S, Pupello D, Saleem A, Mighell M, Vasey M.The rever se shoulder prosthesis for glenohumeral arthritis associated with severe rotator cuff deficiency. A minimum two year follow up study of sixty patients. J Bone Joint Surg Am 2005; 87:1697 705.

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39 24. Frankle MA, Siegel S, Pupello DR, et al. Coronal plane tilt ang le affects risk of catastrophic failure in patients treated with a reverse shoulder prosthesis. Presented at: American Shoulder and Elbow Surgeons 22nd Open Meeting. Chicago, IL; 2006 25. Reinold, MM; Wilk, KE; Fleisig, GS; Zheng, N; Barrentine, SW;Chmielewski T;Cody, RC ;Jameson, CG; Andrews, JR. Electromyographic analysis of the rotator cuff and deltoid musculature during common shoulder external rotation exercises. Journal of orhtopaedics& sports physical therapy. July 2004;34:385 394 26. Ekstrom, RA; Soderberg GL; Donatelli, RA. Normalization procedures using maximum voluntary isometric contractions for the serratus anterior and trapezius muscles during surface EMG analysis. Journal of Electromyography and Kinesiology.August 2005;15:418 428 27. Inman VT, Saunders M, Abbott LC. Observations on the function of the shoulder joint. J Bone Joint Surg 1944; 26A: 1 31. 28. Braman JP, Engel SC, LaPrade RF, Ludewig PM. In vivo assessment of scapulohumeral rhythm during unconstrained overhead reaching in asymptomatic subjects J Shoulder Elbow Surg 2009; 18: 960 7. doi:10.1016/j.jse.2009.02.001 29. Warner JJP, Micheli LJ, Arslanian LE, Kennedy J, Kennedy R. Scapulothoracic motion in normal shoulders and shoulders with glenohumeral instability and impingement syndrome: A study usi ng Moire topographic analysis. Clin Orthop Relat Res 1992; 285: 191 9. 30. Tupling and Pierrynowski, 1987. S.J. Tupling, M.R. Pierrynowski. Use of cardan angles to locate rigid bodies in three dimensional space. Med. and Biol. Eng. and Comput., 25 (1987), pp 527 532 31. Matsuki K,and Banks SA. In vivo 3 dimensional analysis of scapular kinematics: comparison of dominant and nondominant shoulders JSES.2011

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40 BIOGRAPHICAL SKETCH David W alker is from the island of J amaica. He is the only child of A udrey F isher. D avid attended the U niversity of F lorida where he received his B Sc i n M echanical E ngineering. He received his m 2012. He is now pursuing a P h .D. at the U niversity of F lorida in shoulder mechanics modeling