A reduced scapulo-humeral angle contributes to the development of scapular notching in reverse total shoulder arthroplasty.

Purpose: Scapular Notching (SN) is one of the most common postoperative complications for a patient after Reverse Total Shoulder Arthroplasty (RTSA). Despite employing various strategies to mitigate SN risk, the overall incidence remains far from zero. This article introduces a new risk factor, the scapulo-humeral angle (SHA), as a key element influencing the risk for SN.

Methods: A retrospective analysis was conducted on all patients who underwent RTSA for rotator cuff arthropathy at the study centre. The preoperative SHA was measured, and the presence of SN was investigated and graded using the Nerot classification at the latest follow-up.

Results: 42 patients were included. 12 presented SN (incidence 28.5%). A statistically significant Pearson coefficient correlation between pre-operative SHA and the incidence of SN was observed (r= -0.6954; 95% C.I. -0,8250 to -0,4963; p < 0.0001). A statistically significant Pearson coefficient correlation was also found between the degree of SN and the pre-operative SHA (r= -0,7045; 95% C.I. -0,8306 to -0,5096; P value (two-tailed) < 0,0001, alpha 0.05).

Conclusions: The primary finding is a statistically significant correlation between a reduced preoperative SHA and an increased incidence of postoperative SN. The secondary finding is that a smaller preoperative SHA is associated with a more severe degree of SN A SHA cut-off of 50° distinguished patients at high risk of SN from those at low risk. All patients with an SHA below 50° developed SN (10/10), whereas only 6.25% of patients with an SHA exceeding 50° experienced SN (2/32).