Concomitant subscapularis tendon repair in reverse total shoulder arthroplasty and assessment of superior migration of reattachment: a cadaveric biomechanical study

BACKGROUND: Concomitant repair of the subscapularis (SSC) tendon in reverse total shoulder arthroplasty (RTSA) with a lateralized design remains controversial. The present study aimed to evaluate the effect of SSC repair (repair at native insertion, repair at superiorly migrated position, and no repair) on the glenohumeral arc of motion following RTSA in a cadaveric biomechanical setting. METHODS: RTSA was performed on eight cadaveric shoulders under six testing conditions as follows: unrepaired SSC/intact teres minor (TM); intact SSC/intact TM; superiorly repaired SSC/intact TM; unrepaired SSC/deficient TM; intact SSC/deficient TM; and superiorly repaired SSC/deficient TM. Increasing load (2.5-N increments) was applied to the middle deltoid (anterior, posterior; 10 N each, middle; 10- 20 N). The resulting abduction and rotation positions were measured. RESULTS: Unrepaired SSC demonstrated greater abduction and reduced internal rotation (IR), whereas SSC repair increased IR, particularly in TM-deficient models. Superiorly repaired SSC had higher glenohumeral abduction and IR than original SSC repair. SSC repair caused excessive IR in the TM deficiency seen with massive rotator cuff tears. CONCLUSIONS: Concomitant SSC repair in lateralized RTSA decreased glenohumeral abduction and increased IR. Concomitant SSC repair at the original and superiorly migrated footprints should be carefully considered following lateralized RTSA. Level of evidence: V.