Postimpingement instability following reverse shoulder arthroplasty: a parametric finite element analysis |
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| Institution: | 1. Department of Orthopedics and Rehabilitation, University of Iowa, Iowa City, IA, USA;2. Department of Biomedical Engineering, University of Iowa, Iowa City, IA, USA;1. University of Virginia, Charlottesville, VA, USA;2. Jordan-Young Institute, Virginia Beach, VA, USA;3. Banner Health, Phoenix, AZ, USA;4. The Cleveland Shoulder Institute, Beachwood, OH, USA;5. Southern Oregon Orthopedics, Medford, OR, USA;1. TEMA, Biomechanics Research Group, Department of Mechanical Engineering, University of Aveiro, Campo Universitário de Santiago, 3810-193 Aveiro, Portugal;2. ESAD- College of Art and Design, Avenida Calouste Gulbenkian, Senhora da Hora, 4460-268 Matosinhos, Portugal;1. Department of Bioengineering, Clemson University, Clemson, SC, USA;2. Department of Orthopaedics and Physical Medicine, Medical University of South Carolina, Charleston, SC, USA |
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| Abstract: | BackgroundInstability following reverse shoulder arthroplasty is influenced by various factors such as component design, component positioning, and soft tissue tensioning. Patients may achieve glenohumeral motion beyond initial scapular impingement during activities of daily living which could further compound instability. However, instability/subluxation risk postscapular impingement is not well documented. Conventional range of motion analysis tools cannot account for the restraining effect of soft tissues or subluxation risk after impingement. Using a previously validated finite element analysis approach, the purpose of this study was to investigate the effects of glenoid component lateralization and humeral component angle of inclination (AOI), with or without simulated subscapularis repair, on postimpingement subluxation. We hypothesized that lack of subscapularis repair, a valgus humeral component AOI, and glenoid medialization would all result in greater postimpingement instability.MethodsA FE model of the shoulder including the subscapularis tendon and middle deltoid was created, incorporating a general representation of a commercial reverse shoulder arthroplasty implant placed under the direction of a fellowship-trained shoulder surgeon. The deltoid and subscapularis were tensioned and wrapped around the reconstructed glenohumeral joint prior to simulating motion. Humeral rotations were then prescribed to simulate external rotation (neutral to 50°), extension (neutral to 50°), adduction (neutral to 30°), and abduction (neutral to 90°). The effects of three glenosphere lateralization offsets (2, 4, and 10 mm) and 2 humeral liner angles of inclination (varus-150° and valgus-155°) on subluxation propensities were investigated with and without the subscapularis tendon present.ResultsSimulated subscapularis repair resulted in 21%-34% less postimpingement subluxation. Presence of the subscapularis provided stability over a greater range of abduction. Impingement-free range of motion was similar regardless of the presence or absence of the subscapularis. The valgus AOI resulted in 23% less subluxation during abduction. During other motions however, the valgus AOI resulted in 67%-110% greater postimpingement subluxation (subscapularis present), which further worsened without the subscapularis.ConclusionImplant design modifications to improve stability may not be beneficial for all motions, highlighting the importance of directionality when investigating instability. Liner-bone impingement appears to compound instability/subluxation and the subscapularis appears to restrain postimpingement instability.Level of evidenceBasic Science Study; Computer Modeling |
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