Scapular upward rotation during intraoperative functional zero-position assessment in relation to postoperative outcomes and elevated alignment after reverse total shoulder arthroplasty.

PURPOSE: Scapulothoracic (ST) compensation is common after reverse total shoulder arthroplasty (rTSA); however, the clinical relevance of intraoperative scapular motion remains unclear. The functional zero-position denotes humeral shaft-scapular spine alignment during passive scaption. This study evaluated whether scapular upward rotation required to achieve this position was associated with postoperative function and elevated alignment. METHODS: We retrospectively analysed 28 shoulders with cuff tear arthropathy treated with rTSA in which the functional zero-position was fluoroscopically confirmed. Scapular upward rotation angle (SURA) during passive scaption was defined as the change in scapular spine orientation from rest to the functional zero-position. Patients were divided into low- and high-SURA groups using the median SURA. Postoperative range of motion, Constant-Murley Score, and zero deviation angle on maximum active elevation radiographs were compared. RESULTS: The median SURA was 30°. Patients were categorised into low-SURA (≤ 30°, n = 15) and high-SURA (> 30°, n = 13) groups. Flexion was greater in the low-SURA group from three months to the final follow-up (all P < 0.05) and abduction from six months to the final follow-up (all P = 0.019). External and internal rotation did not differ. The Constant-Murley Score was higher in the low-SURA group at 1 year (P = 0.015) and at the final follow-up (P = 0.037). The zero deviation angle was smaller in the low-SURA group at the final follow-up (P = 0.037). CONCLUSION: In this exploratory analysis, the low-SURA group demonstrated superior postoperative elevation, higher Constant-Murley Scores, and elevated alignment closer to the functional zero-position. Intraoperative SURA may represent a potential measure of motion balance during rTSA.