The over-the-top subscapularis repair in reverse shoulder arthroplasty: biomechanical evaluation of a novel technique

Abstract

BackgroundWe evaluate the effect of repairing the upper subscapularis tendon at an alternative location on the anterior greater tuberosity above the center of rotation using a reverse shoulder arthroplasty (RSA) muscle model.MethodsWe compared an innovative subscapularis repair on the anterior aspect of the greater tuberosity with the standard repair on the lesser tuberosity in a previously validated digital linear RSA muscle model. Standard repair vs. a new repair datasets were compared for 3 RSA designs. Each model was run through humeral abduction from 0° to 140° in 2.5° increments; the resulting moment arm measurements (model of tendon efficiency) were recorded in millimeters for 3 sections (superior, middle, inferior). An isolated upper two-thirds subscapularis repair to the anterior greater tuberosity was also evaluated (the over-the-top repair).ResultsThe new over-the-top subscapularis repair significantly increased the abduction moment arm lengths in the superior, middle, and inferior subscapularis components compared with the standard repair to the lesser tuberosity at all levels of glenohumeral abduction and for all 3 RSA designs. Repair of the upper two-thirds of the subscapularis to the new location was an abductor at a much lower level of abduction compared with the native subscapularis repair.ConclusionBy repairing the upper subscapularis tendon above the center of rotation (over-the-top repair) in an RSA muscle model, the subscapularis has an improved movement arm and functions as an abductor through a greater range of motion that may result in clinically increased muscle efficiency and improved strength.

Results after primary reverse shoulder arthroplasty with and without subscapularis repair: a prospective-randomized trial

“…Patients who underwent surgery with a 135° neck-shaft angle prosthesis (Arthrex Universe Reverse) showed better external rotation measured in reachable points in CS 1 year after surgery [10 (6-10) vs. 10 (0-10); p = 0.012, Table 4], compared to those that received a 155° neck-shaft angle prosthesis (DePuy Delta XTend) independent of SSC repair. Patients with a 155° neck-shaft angle prosthesis had a better postoperative force measured in 90° abduction in points of CS [7 (3-25) vs. 4 (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18); p = 0.044, Table 4], compared to patients receiving a 135° neck-shaft angle prosthesis independent of SSC repair.…”

“…Other trials decline the refixation due to postoperative limitation of ROM, especially external rotation, and as no differences in postoperative outcomes after SSC-tendon repair were shown [11][12][13][14]. Other authors tried to address open issues by varying prostheses designs (e.g., medialization/lateralization of prostheses components and variation of the humeral neck-shaft angle) [12,15,16] and different suture techniques of the SSC-tendon [17,18].…”

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].…”

“…While computational modeling may provide a basis for estimates of muscle and joint function, even the most sophisticated anatomical models are limited by the degree to which they replicate bone and joint biomechanics in vivo. Virtually all rigid body models neglect glenohumeral joint translation, and represent the glenohumeral joint as a threedegree-of-freedom constrained ball and socket or spherical joint [21,24,30,[32][33][34][35][36][37][38]40,93]. This simplification limits the degree to which such a model can predict joint stability, since joint subluxation cannot be explicitly simulated.…”