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.
Thesis
The effects of implant design variations on shoulder instability following reverse shoulder arthroplasty
University of Iowa
Master of Science (MS), University of Iowa
Autumn 2018
DOI: 10.17077/etd.skg0-3ob3
Abstract
Details
- Title: Subtitle
- The effects of implant design variations on shoulder instability following reverse shoulder arthroplasty
- Creators
- Andrea Patricia Caceres - University of Iowa
- Contributors
- Donald D. Anderson (Advisor)Jessica E. Goetz (Committee Member)David G. Wilder (Committee Member)Nicole M. Grosland (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Biomedical Engineering
- Date degree season
- Autumn 2018
- DOI
- 10.17077/etd.skg0-3ob3
- Publisher
- University of Iowa
- Number of pages
- xi, 56 pages
- Copyright
- Copyright © 2018 Andrea Patricia Caceres
- Language
- English
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references (pages 53-56).
- Public Abstract (ETD)
Shoulder motion is both stabilized and controlled by four rotator cuff muscles (the subscapularis, infraspinatus, supraspinatus, and teres minor), which act in a coordinated effort to rotate the arm around the glenohumeral joint. Patients with deficiency of the rotator cuff muscles and glenohumeral arthritis experience painful and severely limited glenohumeral motion, which if left untreated can lead to issues such as bone erosion. Reverse shoulder arthroplasty (RSA) allows these patients to regain motion by reversing the anatomical ball-and-socket joint. This enables the deltoid to raise the arm even in the face of the deficient rotator cuff. Although results have been promising, RSA is still a relatively new implant with variable implant design factors that work in tandem with any intact anatomy. This study used finite element analysis to model a shoulder joint with a Zimmer Trabecular Metal RSA system. The model included a fixed scapula with the scapular component of the implant attached, a movable humerus with inserted humeral component of the implant, and soft tissues including the subscapularis, infraspinatus, and deltoid. Six models were made combining different scapular implant lateralizations (2, 4, and 10mm) and humeral liner geometry (normal and retentive). External rotation was simulated on Abaqus Explicit for the shoulder model through 80°. Displacement between the humeral liner and glenosphere center of rotation, contact stress, and deltoid force were recorded and compared for the six models. Models where the shoulder component extended more outwardly from the body were associated with greater impingement-free range of motion at the cost of larger deltoid and subscapularis forces being developed. Although reasonable quantities of deltoid force enhance stability, elevated deltoid forces may contribute to scapular fractures and greater stress at impingement sites post-RSA. Inclusion of more anatomical features as well as other glenohumeral motions can expand upon this study. Ultimately, this modeling approach could provide valuable insights for surgeons to use in planning RSA surgery.
- Academic Unit
- Roy J. Carver Department of Biomedical Engineering
- Record Identifier
- 9983776828502771
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