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.