Date of Degree
MS (Master of Science)
Anderson, Donald D.
First Committee Member
Goetz, Jessica E.
Second Committee Member
Wilder, David G.
Third Committee Member
Grosland, Nicole M.
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.
finite element, glenohumeral joint, orthopedic biomechanics, reverse shoulder arthroplasty, rotator cuff, shoulder biomechanics
xi, 56 pages
Includes bibliographical references (pages 53-56).
Copyright © 2018 Andrea Patricia Caceres
Caceres, Andrea Patricia. "The effects of implant design variations on shoulder instability following reverse shoulder arthroplasty." MS (Master of Science) thesis, University of Iowa, 2018.