The shoulder is the most frequently dislocated joint of the body. Up to 90% of individuals less than 25 years of age that dislocate their glenohumeral joint and have unidirectional anterior instability suffer recurrence that is difficult to diagnose and necessitates surgical repair. Following surgical treatment, return to normal function remains inadequate with unsatisfactory results in 20-25% of patients due to loss of range of motion, recurrent instability, rotator cuff damage, or osteoarthritis. Therefore, research efforts to better understand the function of the passive stabilizers of the shoulder are needed to design better diagnostic protocols and surgical approaches as well as to improve the long-term outcome. The overall hypothesis is that the outcome of shoulder surgery will be improved when the repaired glenohumeral capsule can reproduce the function of the intact shoulder, both at the immediate post-operative periods and in the long-term. Current models of the shoulder stabilizers describe the glenohumeral capsule as a collection of uniaxial elements (glenohumeral ligaments). Therefore, the goal of this project is to perform a comprehensive analysis of the anatomy and biomechanics of the glenohumeral capsule using a novel model of anterior glenohumeral joint stability. The proposed work will utilize a combined experimental and computational approach to characterize the structure and function of the glenohumeral capsule in clinically relevant joint positions. The three Specific Aims of this proposal are: 1) quantify the local multi-axial material properties, microstructural morphology and appropriate constitutive model of the posterior, antero-superior and antero-inferior regions of the glenohumeral capsule as a function of age and gender; 2) develop and validate subject-specific finite element models of the glenohumeral capsule in clinically relevant joint positions; and 3) determine the stress and strain distribution as well as force in the glenohumeral capsule using subject-specific finite element models with the joint in mid-abduction, abduction and apprehension positions. The quantitative data obtained from these innovative and validated models is the first critical step towards the development of new biomechanically based strategies for improved diagnostic procedures and surgical repair following shoulder dislocation. This methodology will also serve as the state-of-the-art for analysis of other joint capsules throughout the musculoskeletal system. ? ?
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