The biomechanics of subscapularis repair in reverse shoulder arthroplasty: The effect of lateralization and insertion site

Abstract

Functional outcomes of subscapularis (SSc) repair following reverse shoulder arthroplasty (RSA) remains controversial. SSc repair in combination with glenosphere lateralization was reported to yield worse clinical outcomes compared with the non‐lateralized glenosphere. The aim of this biomechanical study was to investigate how glenosphere lateralization and different re‐insertion sites can affect the biomechanics of the SSc after RSA. Nine patient‐specific RSA shoulder models were created from patients' computed tomography scans. Moment arms and SSc length were calculated for abduction, forward flexion, and internal rotation in 20° and 90° abduction for three configurations of glenosphere lateralization (standard/+0, +5, and +10 mm) and three SSc repair sites (native, superior, and inferior) and compared with the native shoulder. When compared with the native shoulder, RSA resulted in large adducting SSc moment arms that were antagonistic to the deltoid. Glenosphere lateralization had no effect on SSc moment arms in any motion. However, lateralization increased SSc tension beyond its anatomic length for +5 and +10 mm of lateralization when attached to its native insertion. A superior SSc repair site created the least adductive moment arm as well as the least amount of SSc lengthening. Increased glenosphere lateralization showed a significant increase in the SSc length, which in combination with its adductive moment arm can be antagonistic to deltoid function. However, a superior SSc repair site may help reduce the adductive SSc moment arm and allow for reduced tension on the repair as its length in that location is less than that of the native SSc. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:888‐894, 2020

Extension of the shoulder is essential for functional internal rotation after reverse total shoulder arthroplasty

“…Improving active and passive internal rotation after RTSA has been the focus of various biomelc hanica 1,2,4,6,14,16,19,20,[22][23][24][25][26][27]30,32,33,43,45 and clinical 5,21,[35][36][37]39,42,44 studies. The most important finding of our study is that active extension of at least 40 is a prerequisite for satisfactory fIR after RTSA.…”

A pilot-study focusing on internal rotation after reverse total shoulder arthroplasty using the Activities of Daily Living which require Internal Rotation (ADLIR) score

“…17,18 The subscapularis tendon Biomechanic and functional implications of subscapularis tendon repair have been investigated thoroughly in patients treated with reverse total shoulder arthroplasty. [18][19][20] Whether to repair the subscapularis tendon or not remains an interesting topic in the field of reverse total shoulder arthroplasty. Friedman et al reported excellent outcomes after RTSA for both patients with and without subscapularis repair with a follow-up comparable to this present study.…”

Complications of Reverse Total Shoulder Arthroplasty: A Computational Modelling Perspective

“…Computational modeling of RTSA facilitates estimation of muscle and joint loading, which is currently impossible to measure non-invasively in vivo. Modeling and simulation of RTSA has played a critical role in guiding implant positioning and surgical technique [19][20][21][22], prosthesis selection [23,24], implant design [25,26], and post-operative rehabilitation prescription [27,28]. To date, most modeling and simulation tools require high levels of expertise and are generally restricted to the research setting.…”

“…For example, shoulder muscle forces during upper limb elevation can be calculated in several minutes using a subject-specific rigid body model (Figure 1A) [28,31]; however, since deformation mechanics is neglected, the internal stresses and strains in the bone and implant cannot be accurately evaluated using this method. An important utility of rigid body models has been in their capacity to estimate the influence of arthroplasty on muscle moment arms, muscle and joint forces, and range of motion (ROM) at the shoulder, which are primary indicators of implant functional performance [21,23,24,[29][30][31][32][33][34][35][36][37][38][39][40].…”