Preoperative diagnosis and rotator cuff status impact functional internal rotation following reverse shoulder arthroplasty

Purpose This study aimed to evaluate whether functional internal rotation (fIR) following reverse shoulder arthroplasty (RSA) differs based on diagnosis of either: primary osteoarthritis (OA) with intact rotator cuff, massive irreparable rotator cuff tear (MICT) or cuff tear arthropathy (CTA). Methods A retrospective review was performed on RSAs performed by a single surgeon with the same implant over a five year period. Minimum two year follow-up was available in 235 patients; 139 (59.1%) were females, and the mean patient age was 72±8 years. Additional clinical evaluation included the simple shoulder value (SSV) and Constant score. Postoperative internal rotation was categorized as type I: hand to the buttock or hip, type II: to the lower lumbar region, or type III smooth motion to at least the upper lumber region. Type I was considered "non-functional" internal rotation and type II or III were fIR. . Results Preoperatively, internal rotation was classified as type I in 60 (25.5%) patients, type II in 114 (48.5%), and type III in 62 (26%). Postoperatively internal rotation was classified as type I in 70 (30%) patients, type II in 86 (36%), and type III in 79 (34%). Compared to preoperative status, fIR improved significantly in OA patients (p<0.001), with 49 (52.6%) classified as type II or III postoperatively. In CTA patients, there was no significant change (p=0.352). In patients with MICTs, there was significant loss in fIR postoperatively (p=0.003), with 25 (30.8%) patients deteriorating to type I after having either type II or III preoperatively, and only five (6.1%) patients improving to either type II or III. Conclusions Patients who undergo RSA for primary OA have a better chance of postoperative fIR improvement. A decrease in fIR is common after RSA for MICTs.