OTSR - 2026-05-01 - Journal Article
How does subscapularis repair affect joint loads? Effect of humeral tray thickness in Reverse Total Shoulder Arthroplasty (rTSA).
Caubère A, Rutigliano S, Bourdon S, Erickson J, Morelli M, Parsons M, Neyton L, Gauci MO
Topics
Key Takeaway
Subscapularis repair significantly recenters glenohumeral contact loads in rTSA at 6 mm humeral lateralization, reducing load centroid radial distance to 0.2 mm versus 0.9 mm without repair (p<0.001) in abduction, behind-back, and overhead-reach positions.
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Summary
This cadaveric biomechanical study evaluated whether subscapularis repair and incremental humeral tray thickness (0–6 mm) affect glenohumeral contact loads and centroid location in rTSA across seven positions. Using a proprietary load-sensing system (Goldilocks, Statera Medical), increasing humeral offset alone recentered loads in most positions, but subscapularis repair added a significant recentering effect, particularly at 6 mm lateralization in abduction, behind-back, and overhead-reach (|r| 0.2 mm vs. 0.9 mm, p<0.001). Subscapularis repair also independently increased joint loads at maximal humeral lateralization, suggesting a combined stabilizing and compressive role.
Key Limitation
A sample size of two shoulders is insufficient to support statistical conclusions; the reported p-values and ICC must be interpreted as descriptive pilot data only.
Original Abstract
BACKGROUND
This study aimed to evaluate how subscapularis tendon repair influences joint loads in relation to humeral offset and arm position.
PATIENTS AND METHODS
Two fresh-frozen, whole-body cadaveric shoulders underwent a reverse total shoulder arthroplasty (rTSA) on the humeral side using an internal proprietary load-sensing system (LSS) (Goldilocks, Statera Medical, Montreal, Canada). In addition to three "complex" Activity Daily Life positions ("behind the back", "overhead reach", and "across the chest"), four standard postures (external rotation, extension, abduction, and flexion) were used to record the glenohumeral loads (Newtons) and their locations applied to the implant. The humeral system's adjustability function was used to gradually raise the thickness for each setting from 0 to 6 mm. The first part of the tests consisted of taking these measurements with the repaired subscapularis tendon. Once all the measurements had been taken, the tendon was detached, and the same measurements were repeated in the same order. Load and contact point were measured using the load centroid radial distance (|r|).
RESULTS
The measurements showed good repeatability with an intra-class correlation coefficient (ICC) greater than 0.9 for all positions. Increasing the thickness of the humeral implant from 0 to 6 mm, without subscapularis, resulted in a refocusing of loads on the humeral cup for several positions, except for abduction at 60° (|r| 0mm = 1 mm VS |r| 6mm = 0.9 mm; p = 0.570), cross body (|r| 0mm = 0.7 mm VS |r| 6mm = 0.5 mm; p = 0.413) and overhead reach (|r| 0mm = 1 mm VS |r| 6mm = 0.9 mm; p = 0.284). Subscapularis repair enhances this recentering effect for all positions, with a particularly significant influence on abduction at 60°, "behind back" and "overhead reach" (|r| 6mm = 0.2 mm VS 0.9 mm, p < 0.001). Subscapularis repair also significantly increased joint loads for these positions at 6 mm humeral lateralization.
DISCUSSION
The findings of this biomechanical study provide substantial evidence to support the hypothesis that the subscapularis muscle plays a pivotal role in the process of refocusing joint loads in rTSA. Consequently, subscapularis repair may exert a biomechanical effect on rTSA stabilisation.
LEVEL OF EVIDENCE
V; Biomechanical study.