Les tendinopathies sont la première cause de maladie professionnelle en France. Elles sont devenues une préoccupation majeure de santé publique. Cependant, leurs mécanismes physiopathologiques restent encore mal définis. Au cours de cette thèse, nous nous sommes intéressés aux phases précoces de la tendinopathie engendrées par une sur-utilisation du tendon supra-épineux (tSE) de la coiffe de rotateurs de l’épaule chez le rat. Nous avons tenté de comprendre les mécanismes à l’origine de cette pathologie afin de pouvoir agir et la traiter en amont de l’apparition des symptômes.Nous montrons que le profil d’évolution moléculaire des collagènes, des protéoglycanes et des glycosaminoglycanes (GAGs) associé aux phases précoces de la sur-utilisation, témoigne d’un profond remaniement matriciel et d’une différenciation chondroïde des fibroblastes tendineux. Nous avons identifié les métalloprotéinases (MMPs) majeures et leurs inhibiteurs (TIMPs) susceptibles d’être impliqués dans ce remaniement. Nos résultats suggèrent que le mécanisme lésionnel initial et les changements matriciels observés sont dus à un processus induit par des médiateurs locaux libérés par les ténocytes et non à une réaction inflammatoire. Enfin, nous avons cherché à établir une corrélation entre les changements moléculaires observés et le degré de sévérité d’une tendinopathie diagnostiquée chez l’Homme. Nous avons montré, sur des échantillons de tendon patellaire humain une relation entre la quantité des GAGs et le score (VISA score) reflétant le degré pathologique du tendon.Cette étude nous a donc permis d’améliorer nos connaissances des phases précoces du processus d’altération du tSE. Cependant, d’importants efforts restent néanmoins à accomplir dans la caractérisation de la pathogenèse précoce notamment pour préciser le contexte biomécanique qui la génère. / Tendinopathies are the first cause of professional diseases in France. They are a major public health concern. However, their physiopathological mechanisms remain poorly understood. This project aimed at investigating the early stages of supraspinatus tendinopathy caused by overuse. Using a rat animal model, we attempted to understand the mechanisms behind this disease in order to act and treat the symptoms upstream of their onset.We have shown that the molecular changes of collagens, proteoglycans and glycosaminoglycans (GAGs) associated with the early events of overuse attest a major matrix remodeling and chondrogenic differentiation of tendon cells. We identified the main metalloproteinases (MMPs) and their inhibitors (TIMPs) that may be involved in this remodeling. Our results further suggest that the initial mechanisms linked to the observed matrix changes are due to local mediators release by tenocytes rather than an inflammatory process. Finally, we attempted to correlate molecular changes observed during overuse with the severity of the tendinopathy diagnosed in humans. We have shown a relationship between the amount of GAGs and the pathological score (VISA score) on human patellar tendons.This study improved our knowledge of the early pathological events of the supraspinatus tendon. However, more remains to be done for characterizing the early stages of tendinopathy especially to clarify the biomechanical context up-stream.

INTRODUÇÃO: Na patogênese da rotura do manguito rotador, diminuição da síntese e aumento da degradação das fibras colágenas são encontradas, associadas ao aumento da atividade das metaloproteinases da matriz 1 e 3 (MMP-1 e MMP-3). Há evidências que fatores genéticos estão envolvidos na produção das metaloproteinases e na etiologia da rotura do manguito rotador. O objetivo deste estudo foi avaliar a associação entre o polimorfismo genético das MMP-1 e MMP-3 com a rotura de espessura completa do manguito rotador. Como objetivos secundários, tivemos avaliar a correlação dos haplótipos da MMP-1 e MMP-3 com a rotura de espessura completa do manguito rotador e comparar se indíviduos com rotura transfixante do manguito rotador têm maior proporção de familiares com a mesma doença, em relação aos indíviduos controles. MÉTODOS: Avaliamos 64 pacientes com rotura transfixante do manguito rotador e 64 controles assintomáticos. Foram incluídos apenas pacientes com idade inferior a 65 anos e rotura de espessura completa não traumática. A rotura ou integridade do manguito rotador foi avaliada por ressonância magnética ou ultrassonografia em todos indivíduos. Os pacientes e os controles foram pareados por idade. O ácido desoxirribonucleico (DNA) dos voluntários foi obtido a partir de células epiteliais da mucosa bucal. Os genótipos das MMP-1 e MMP-3 foram determinados utilizando as técnicas de Reação em Cadeia de Polimerase (PCR) e Polimorfismo no Comprimento de Fragmentos de Restrição (RFLP). RESULTADOS: Observamos uma presença de 77% do alelo 1G e 64% do genótipo 1G/1G no grupo controle. Os pacientes com rotura transfixante do manguito rotador apresentaram uma taxa de 48% do alelo 2G e 73% de genótipos 1G/2G ou 2G/2G (p < 0,001). Indivíduos com genótipo 1G/2G e 2G/2G tiveram maior chance de ter uma rotura do manguito rotador: razão de chances (RC) igual a 4,8 (Intervalo de confiança de 95% [IC 95%] 2,1 a 11,0) e 5,2 (IC 95% 1,8 a 14,9), respectivamente. Também observamos uma distribuição significativamente diferente nos alelos e genótipos da MMP-3 (p = 0,045, p = 0,021, respectivamente) entre os casos e controles. Indivíduos com genótipo 5A/5A tiveram maior chance de apresentarem uma rotura do manguito rotador (RC 5,5; IC 95% 1,4 a 20,9). Indíviduos com haplótipo 2G/5A tiveram maior possibilidade de ter uma rotura do manguito rotador, este haplótipo foi encontrado em 42 de 64 pacientes (66%) e em 17 de 64 controles (27%), com razão de chances de 5,3 (IC 95% 2,5 a 11,3). Pacientes com rotura do manguito rotador relataram, em maior número (19 de 64 pacientes, 30%), a existência de familiares que realizaram tratamento para rotura do manguito rotador em relação aos pacientes controles (quatro de 64 pacientes, 6%; p = 0,001). CONCLUSÃO: O polimorfismo genético das MMP-1 e MMP-3 foi associado à rotura do manguito rotador / INTRODUCTION: In the pathogenesis of rotator cuff tear, decreased synthesis and increased degradation of collagen fibers are found, associated with an increase in activity of matrix metalloproteinases 1 and 3 (MMP-1 and MMP-3). There is evidence that genetic factors may be involved in metalloproteinase production and the etiology of rotator cuff tear. The aim of this study was to evaluate the association between the genetic polymorphism of MMP-1 and MMP-3 and full-thickness rotator cuff tear. As secondary aims, we measured the correlation of MMP-1 and MMP-3 haplotypes with full-thickness rotator cuff tears and compared if individuals with full-thickness rotator cuff tears have a higher proportion of relatives with the same disease than the control subjects. METHODS: We evaluated 64 patients with full-thickness rotator cuff tear and 64 asymptomatic controls. Patients aged below 65 years, with non-traumatic full thickness tears, were included. The rotator cuff tear or integrity was evaluated by magnetic resonance or ultrasound in all individuals. The patients and controls were paired by age. The deoxyribonucleic acid (DNA) of the volunteers was obtained from oral mucosa epithelial cells. MMP-1 and MMP-3 genotypes were determined using the Polimerase Chain Reaction (PCR) and Restriction Fragment Length Polymorphism (RFLP) assays. RESULTS: We observed a 77% presence of allele 1G and 64% of genotypes 1G/1G in the control group. The patients with full-thickness rotator cuff tear presented 48% of allele 2G and 73% of genotypes 1G/2G or 2G/2G (p < 0.001). Individuals with genotypes 1G/2G and 2G/2G were more likely to have a rotator cuff tear: odds ratio equal to 4.8 (95% confidence interval [95% CI] 2.1 to 11.0) and 5.2 (95% CI 1.8 to 14.9), respectively. We also observed a significantly different distribution in the alleles and genotypes of MMP-3 (p = 0.045, p = 0.021, respectively) among the cases and controls. Individuals with the 5A/5A genotype were more likely to have a rotator cuff tear (OR 5.5; 95% CI 1.4 to 20.9). Individuals with the haplotype 2G/5A were more likely to have rotator cuff tears develop, this haplotype was found in 42 of 64 patients (66%) and in 17 of 64 controls (27%) with odds ratio 5.3 (95% CI 2.5 to 11.3). Patients with rotator cuff tears reported, in higher number (19 of 64 patients, 30%), the existence of relatives who previously had treatment for rotator cuff tears compared to control patients (four of 64 patients, 6%; p = 0,001). CONCLUSION: The genetic polymorphism of MMP-1 and MMP-3 was associated with rotator cuff tear

Os músculos do manguito rotador são os responsáveis pelo movimento de rotação do ombro e representam sítio freqüente de processos patológicos.O desequilíbrio de forças do manguito rotador pode desencadear patologias distintas do ombro ou ser resultado destas. A quantificação da força muscular do manguito rotador com dados precisos, somente é possível com aparelhos de alto custo, longe do alcance da maioria dos profissionais envolvidos com o problema em nosso país. No presente estudo, um aparelho relativamente simples e de baixo custo, capaz de mensurar com precisão a força muscular isométrica de rotação interna e rotação externa do ombro, foi projetado e construído com materiais de fácil obtenção e preço acessível. Ele consiste basicamente de uma plataforma de medição do torque de rotação do ombro acoplada a uma cadeira e adaptável para avaliação bilateral. O aparelho foi projetado para que o indivíduo permaneça sentado durante o teste, com cotovelo fletido a 90 graus e o antebraço apoiado sobre uma superfície plana. Um torquímetro, devidamente calibrado, foi fixado na porção inferior da plataforma, no ponto correspondente ao centro de rotação do ombro. A mudança no comprimento do braço de alavanca foi permitida pela variação na posição de um manípulo para apoio da mão durante os esforços de rotação interna e de rotação externa do ombro. Variações no comprimento do braço de alavanca e na altura da plataforma foram projetadas para adaptarem-se aos braços e antebraços dos indivíduos. O aparelho foi testado em 20 indivíduos saudáveis e demonstrou ser completamente versátil para uso em diversas condições e confiável na produção de informações sobre o torque dos músculos rotadores do ombro. / The rotator cuff muscles are responsible for the rotation movements of the shoulder and frequent site of pathological processes. Rotator cuff muscle power imbalance may unchain or result from distinct shoulder diseases. To date precise quantification of rotator cuff muscle power is only possible with the use of expensive machines, far from the reach of most of the professionals involved with the problem in our country. In the present investigation, a relatively simple and low cost device, able to precisely measuring isometric internal and external rotator muscle power, was developed and built with easily obtainable and low cost materials. It consists basically of a platform for measuring the rotational torque of the shoulder adaptable to both sides of a chair for bilateral evaluation. It was designed for the individual to remain seated while in test, the elbow flexed at 90o and the forearm rested on a flat surface. A properly calibrated torquimeter was adapted to the bottom side of the platform in a point corresponding to the shoulder’s center of rotation. The moving lever was provided with a handle to be grasped by the individual while doing internal or external efforts with the shoulder. Both platform height and moving lever were made adaptable to individual arm and forearm lengths. The device was tested with 20 healthy individuals and demonstrated to be quite versatile for use in many different conditions and reliable in providing information on the torque of the rotator muscle of the shoulder.

Os mecanismos antecipatórios durante as tarefas de alcance são de extrema importância para o equilíbrio corporal e para facilitação da execução do movimento. Há evidências na literatura que a dor crônica é capaz de influenciar na organização funcional do córtex e alterar os ajustes posturais antecipatórios, mas, até o presente conhecimento, não existe nenhum estudo que investigou estes mecanismos posturais em indivíduos com dor crônica no ombro. Por este motivo, o objetivo principal do presente estudo foi analisar os ajustes posturais antecipatórios em uma tarefa de alcance funcional em indivíduos com dor no ombro comparados a indivíduos sem dor. Participaram do estudo 20 sujeitos, sendo 9 no grupo com dor e 11 no grupo sem dor. Dados de eletromiografia dos músculos de tronco e membro inferior direito e dados de plataforma de força foram coletados durante uma tarefa de alcance funcional realizada em diferentes velocidades (rápida e normal) e alturas (menor que 90°, igual a 90° e maior que 90°). O grupo com dor apresentou menor amplitude e velocidade de deslocamento do centro de pressão, atraso no recrutamento antecipatório do músculo tibial anterior, alteração da sinergia muscular de membro inferior e tronco, atraso no tempo de resposta, maior tempo de execução do movimento e menor variabilidade do movimento. Não houve correlação entre a intensidade da dor e as alterações de comportamento motor. Os resultados mostram que indivíduos com dor no ombro apresentam falha no ajuste postural antecipatório durante uma tarefa de alcance funcional quando comparados com indivíduos sem dor / Anticipatory mechanisms during reaching tasks are extremely important for body balance and for facilitating movement execution. There is evidence in the literature that chronic pain can influence the functional organization of the cortex and alterate the anticipatory postural adjustments, but to the present knowledge, there is no study investigating of these postural mechanisms in individuals with chronic shoulder pain. For this reason, the main objective of this study is to analyze the anticipatory postural adjustments in a task of functional reach in individuals with shoulder pain compared to individuals without pain. Twenty people participated in the study, 9 in the pain group and 11 in the painless group. Electromyography data of the right trunk and lower limb muscles and force platform data were collected during a functional range task performed at different velocities (fast and normal) and heights (less than 90°, equal to 90° and greater than 90°). The pain group showed lower amplitude and pressure center displacement velocity, delayed anticipatory recruitment of the anterior tibial muscle, altered lower limb and trunk muscle synergism, delayed response time, longer execution time and less movement variability. There was no correlation between pain intensity and changes in motor behavior. The results show that individuals with shoulder pain present failure in anticipatory postural adjustment during a task of functional range when compared to individuals without pain

Functional integration of bone with soft tissues such as tendon is essential for joint motion and musculoskeletal function. This is evident in the rotator cuff of the shoulder, which consists of four muscles and their associated tendons that connect the humerus and scapula. The cuff functions to stabilize the shoulder joint, and actively controls shoulder kinematics. Rotator cuff injuries often occur as a result of tendon avulsion at the tendon-bone interface, with more than 250,000 cuff repair surgeries performed annually in the United States. However, these procedures are associated with a high failure rate, as re-tears often occur due to the lack of biological fixation of the tendon to bone post-surgery. Instead of regenerating the tendon-bone interface, current repair techniques and augmentation grafts focus on improving the load bearing capability of the repaired rotator cuff. Biologically, the supraspinatus tendon inserts into bone via a biphasic fibrocartilaginous transition, exhibiting region-dependent changes in its compositional, structural and mechanical properties, which enables efficient load transfer from tendon to bone as well as multi-tissue homeostasis. Inspired by the native tendon-bone interface, we have designed and evaluated a biomimetic bilayer scaffold, comprised of electrospun poly (lactide-co-glycolide) (PLGA) nanofibers seamlessly integrated with PLGA-hydroxyapatite (HA) fibers, in order to engineer tendon-bone integration. The objective of this thesis is to explore the key design parameters that are critical for integrative tendon-bone repair using this biphasic scaffold as a model. Specifically, intrinsic to the scaffold, effects of fiber alignment, fiber diameter, mineral distribution, and polymer composition on integrative rotator cuff tendon-bone healing were evaluated in vivo using a rat model. Results indicated that an aligned, nanofiber-based scaffold with a distinct order of non-mineralized and mineralized regions will lead to insertion regeneration and integrative tendon-bone repair. Additional tissue engineering design parameters such as healing time and animal model were also tested. It was observed that the biphasic scaffold exhibited a stable long term response, as the mechanical properties of rat shoulders repaired by this scaffold remained comparable to that of the control at 20 weeks post-surgery. This scaffold was also evaluated in a large animal model (sheep), in which a clinically-relevant rotator cuff repair procedure was implemented with the biphasic scaffold. Results demonstrated the scaffold lead to integrative rotator cuff repair through the regeneration of the enthesis in both small and large animal models. In summary, through a series of in vivo studies, the work of this thesis has identified the critical tissue engineering parameters for integrative and functional rotator cuff tendon repair. More importantly, the design principles elucidated here are anticipated to have a broader impact in the field of tissue engineering, as they can be readily applied towards the regeneration of other soft-hard tissue interfaces.

Reverse shoulder arthroplasty (RSA) is performed to decrease pain and improve function and range of motion (ROM) primarily for patients with rotator cuff arthropathy, an arthritis of the shoulder secondary to rotator cuff insufficiency. However, RSA has suffered from high early to mid-term rates of complication, with instability being one of the most common. The shoulder biomechanics post-RSA depend on multiple factors such as implant geometry, positioning, and cuff integrity. This study built upon prior finite element (FE) analysis of RSA to investigate the effects of glenoid lateralization and retentive liner design on shoulder stability. A previously validated FE model was extended to model shoulder external rotation (ER) after implantation of the Zimmer Trabecular Metal RSA system. The FE model included the scapula bone with an implanted glenosphere implant, the humerus bone with implanted humeral sections of the RSA implant, and muscle tendons representing the subscapularis, infraspinatus, and deltoid. Six different models matched glenospheres in three cases of lateralization (2mm, 4mm, and 10mm) with two humeral poly liner designs (normal: 150° neck shaft angle or retentive: 155° neck shaft angle). Using Abaqus/Explicit FE software, the proximal ends of the soft tissues were pulled to their anatomical positions, and then fixed in space while the humerus was externally rotated 80° about the humeral long axis from a neutral position with the shoulder abducted 25°. The displacements, deltoid and subscapularis forces, impingement-free ROMs, and subluxation gap distances were recorded. Although greater glenosphere lateralization was associated with higher impingement-free ROM, larger deltoid and subscapularis forces developed. Deltoid tension contributes to shoulder stability and control, but elevated amounts of deltoid tension may contribute to scapular fractures and greater stress at impingement sites post-RSA. Further analysis such as inclusion of more anatomical features and additional motions may offer greater insight to orthopedic surgeons when planning for RSA insertion.

Syftet med avhandlingen var att beskriva diagnostiken och utvärdera handläggningen i primärvård av patienter med subacromial smärta. Avhandlingen omfattar fyra studier. I den första studien användes ett frågeformulär och resultaten beskriver hur distriktsläkare och distriktssjukgymnaster i ett svenskt län diagnosticerar och handlägger primärvårdspatienter med subacromial smärta. Den andra studien beskriver distriktsläkares och distriktssjukgymnasters tilltro till effekten av olika behandlingsmetoder för dessa patienter. Med utgångspunkt från de tilltrodda behandlingsmetoderna genomfördes en systematisk litteraturöversikt. Den tredje studien utvärderar intra- och interbedömar reliabilitet för ett styrketest som ingår i ett utvärderingsinstrument ‘the Constant-Murley shoulder assessment’. Den avslutande studien är en randomiserad klinisk studie som utvärderar och jämför effekten av två behandlingsstrategier, akupunktur och ultraljud, båda i kombination med hemträning. Distriktsläkare och distriktssjukgymnaster visade sig använda en likartad diagnostik. Det troligaste valet av behandling för distriktsläkare var antiinflammatoriska läkemedel och kortisoninjektion i den subacromiala bursan och för distriktssjukgymnaster rörelseträning samt ergonomiska åtgärder. Dock var de flesta behandlingsalternativen troliga val, vilket tolkas som en osäkerhet om behandlingarnas effekt. Med utgångspunkt från de behandlingsmetoder som distriktsläkare och distriktssjukgymnaster tilltrodde som effektiva för patienter med subacromial smärta, genomfördes en systematisk kritisk litteraturöversikt. Fyrtio studier inkluderades och deras evidensnivå utvärderades. Endast kortisoninjektion i den subacromiala bursan visade sig ha definitiva bevis för effekt. Akupunktur visade sig ha troliga bevis för effekt och ultraljudsbehandling konkluderades som ineffektivt för patienter med subacromial smärta. Det förelåg en låg grad av samstämmighet mellan tilltro och tillgängliga vetenskapliga bevis. En digital dynamometer kan ersätta den konventionella fjädervågen i det standardiserade styrketestet. En nästan perfekt överensstämmelse vad gäller både intra- och interbedömarreliabilitet vid test av unga skulderfriska personer, oberoende av om en ”håll emot-” eller ”dragteknik” användes eller om medel- eller maxvärden användes vid beräkningen av överensstämmelse. I den randomiserade kliniska studien inkluderades 85 patienter. Tre utvärderingsinstrument, kombinerade i resultatanalysen, utvärderade förändringen under en uppföljningsperiod på 12 månader tillsammans med patienternas subjektiva skattning av resultatet. Resultaten visade att akupunktur i kombination med hemträning är att föredra. Båda behandlingsgrupperna förbättrades signifikant och fortsatte förbättras över tid oberoende av behandling. De flesta patienter uppnådde ett tillfredställande behandlingsresultat efter 12 månader. Åtminstone tre fjärdedelar i varje behandlingsgrupp skattade sig mycket förbättrade eller helt återställda. Detta tolkas som en behandlingseffekt i kombination med naturalförloppet. Avhandlingen har beskrivit handläggningen i primärvård av patienter med subacromial smärta och har bidragit med vetenskapliga bevis för distriktsläkare att behandla med kortisoninjektion i subacromiala bursan och för distriktssjukgymnaster att behandla med akupunktur kombinerat med hemträning. / The aim of the thesis was to describe the diagnostic approach and evaluate primary care management of patients with subacromial pain. The thesis includes four different studies, a questionnaire study describing attitudes among general practitioners and physiotherapists in a Swedish county toward the diagnostic approach and management of primary care patients with subacromial pain; a combination of a systematic review and general practitioners and physiotherapists beliefs in interventions for patients with subacromial pain; a study of intra- and inter-observer reliability for the strength test in the Constant-Murley shoulder assessment; and a randomised clinical trial to evaluate and compare the efficacy of two treatment strategies for patients with subacromial pain, acupuncture combined with home exercises and continuous ultrasound combined with home exercises. In the questionnaire study we described that general practitioners and physiotherapists have a uniform diagnostic approach. The most probable choice of treatment was non-steroidal anti-inflammatory drugs and corticosteroid injection into the subacromial bursa for general practitioners and movement exercises together with ergonomics/adjustments at work for physiotherapists, but most treatments were probable choices, reflecting an uncertainty about their effectiveness. The treatments trusted by general practitioners and physiotherapists were systematically reviewed. Forty studies were included and the level of evidence was summarised. Only corticosteroid injections into the subacromial bursa, had definitive evidence for efficacy. Acupuncture had tentative evidence for efficacy and therapeutic ultrasound was concluded as ineffective for patients with subacromial pain. The association between trusted treatments and available scientific evidence was weak. A digital dynamometer can replace the conventional spring-balance in the standardised strength test. An almost perfect agreement was found for intra- and inter-observer reliability in young shoulder-healthy persons, regardless of whether a 'resisted-force' or a 'pull-force' was used or if calculated with mean or maximum values. Eighty-five patients were included in the randomised clinical trial. Three shoulder scores, combined in the analysis, measure change during a 12 months follow-up together with a ‘patient self-evaluation’ of the experienced result. The results favoured acupuncture combined with home exercises. Both groups improved significantly and continued to improve over time independent of treatment and most of the patients reached a satisfactory result at 12 months. At least three fourths of the patients, in each treatment group, reported large improvements or felt completely recovered. This is interpreted as a combination of treatment effect and the natural course. This thesis has described the primary care management of patients with subacromial pain and provided scientific evidence for general practitioners to use corticosteroid injection and for physiotherapists to use acupuncture combined with home exercises, when treating these patients. / On the day of the defence date the status on article III was Accepted and article IV was Submitted.

The aim of this thesis was to study different aspects of the soft tissues of the shoulder joint. The variation in the quality of the tendons and ligaments can be explained by genetic factors. To test the hypothesis that collagen 1 α1 Sp1 polymorphism is related to the occurrence of cruciate ligament ruptures and shoulder dislocations, a total of 358 patients (233 patients with cruciate ligament ruptures and 126 with shoulder dislocations) were included in the study. We found a decreased risk of these injuries associated with collagen type 1 α1 Sp1 polymorphism. To study the mechanical properties of a better type of fixation of soft tissue to bone, 10 skeletally mature New Zealand white rabbits were operated bilaterally on the knees. The medial collateral ligaments were fixed by two types of plates one with a flat undersurface and the other with a pegged undersurface. After 4 weeks the force at failure, stiffness and energy uptake was almost double in the knees operated with the pegged plates. The prevalence and dysfunction of rotator cuff tears was investigated in 106 subjects who had never sought for their shoulder complaints, using Constant score, ultrasound and plain x-ray. The prevalence of full-thickness cuff tears was 30% (21% of all shoulders). The Constant score was lower in subjects with full-thickness tears. Partial-thickness tears and acromioclavicular joint osteoarthritis had no impact on shoulder complaints or Constant score. The subacromial index was lower for shoulders with full-thickness tears. Forty-eight patients with median age 56 years underwent subacromial decompression with or without acromioclavicular joint resection, investigated with MRI pre- and 3 months postoperatively. The Constant score and subjective shoulder value were measured preoperatively and at 3 and 6 months after surgery and even 2 years for subjective shoulder value. Two raters investigated the MRI. The results showed poor inter-rater reliability for MRI. However, both Constant score and subjective shoulder value improved over time. MRI is not a reliable method to study the capsular reaction after subacromial decompression due to high subjectivity of the radiologists.

Computer generated three-dimensional (3-D) models are being used at increasing rates in the fields of entertainment, education, research, and engineering. One of the aspects of interest includes the behavior and function of the musculoskeletal system. One such tool used by engineers is the finite element method (FEM) to simulate the physics behind muscle mechanics. There are several ways to represent 3-D muscle geometry, namely a bulk, a central line of action and a spline model. The purpose of this study is to exmine how these three representations affect the overall outcome of muscle movement. This is examined in a series of phases with Phase I using primitive geometry as a simplistic representation of muscle. Phases II and III add anatomical representations of the shoulder joint with increasing complexity. Two methods of contraction focused on an applied maximal force (Fmax) and prescribed displacement. Further analyses tested the variability of material properties as well as simulated injury scenarios. The results were compared based on displacement, von Mises stress and solve time. As expected, more complex models took longer to solve. It was also supported that applied force is a preferred method of contraction as it allows for antagonistic and synergistic interaction between muscles. The most important result found in these studies was the consistency in the levels of displacement and stress distribution across the three different 3-D representations of muscle. This stability allows for the interchangeability between the three different representations of muscles and will permit researchers to choose to use either a bulk, central line of action or a spline model. The determination of which 3-D representation to use lies in what physical phenomenon (motion, injury etc.) is being simulated.

Unbalanced muscle forces in the shoulder joint may lead to functional impairment in the setting of rotator cuff tear and progressive arthritis in cuff tear arthropathy. A model, which predicts muscle forces for common shoulder movements, could be used to help in treatment decision-making and in improving the design of total shoulder prosthesis. Unfortunately, the shoulder has many muscles that overlap in function leading to an indeterminate system. A finite element model employing an optimization algorithm could be used to reduce the number of degrees of freedom and predict loading of the glenohumeral joint. The goal of this study was to develop an anatomically and physiologically correct computational model of the glenohumeral joint. This model was applied to: 1) estimate the force in each muscle during the standard glenohumeral motions (flexion/extension, abduction/adduction and internal/ external rotation), and 2) determine stress concentrations within the scapula during these motions. These goals were realized through the following steps: First, a three dimensional bone reconstruction was performed using computed tomography (CT) scan data. This allowed for a precise anatomical representation of the bony components. Then muscle lever arms were estimated based on the reconstructed bones using computer-aided design software. The origins, insertions, and muscle paths were obtained from the literature. This model was then applied to estimate the forces within each of the muscles that are necessary to stabilize the joint at a fixed position. Last, finite element analysis of the scapula was performed to study the stress concentrations. These were identified and related to the morphology of the bone. A force estimation algorithm was then developed to determine the necessary muscle force distribution. This algorithm was based on an applied external moment at the joint, and the appropriate selection of muscles that could withstand it, ensuring stability, while keeping the reaction force at a minimum. This method offered an acceptable solution to the indeterminate problem, a unique solution was found for each shoulder motion. The model was then applied to determine the stress concentration within various regions of the scapula for each of the shoulder motions. The rotator cuff was found to act as the main stabilizer under rotation, and had a significant stabilizing role under flexion and abduction. The finite element model of the shoulder that was developed can be used to gain a better understanding of the load transfer mechanisms within the glenohumeral joint and the impact of muscle forces on scapular morphology. This information can then be used to assist with treatment decision-making for rotator cuff tears and with the design of new implants for total shoulder arthroplasty.