Lateral acromioplasty cannot sufficiently reduce the critical shoulder angle if preoperatively measured over 40°.

Purpose: To investigate whether arthroscopic lateral acromion resection can sufficiently reduce the critical shoulder angle (CSA) without damaging deltoid muscle insertion.

Methods: Ninety patients who underwent arthroscopic rotator cuff (RC) repair were retrospectively analysed. According to the preoperative CSA, patients were categorized as Group I (CSA < 35°) and Group II (CSA ≥ 35°). Additional arthroscopic lateral acromion resection was performed in Group II. The CSA was measured 1 week postoperatively, while RC integrity and the deltoid attachment were assessed at 3, 6 and 12 months via ultrasound. Deltoid function was evaluated using the Akimbo test, in which patients place their hands on the iliac crest with abduction in the coronal plane and internal rotation of the shoulder joint while simultaneously flexing the elbow joint and pronating the forearm.

Results: Large and massive RC tears were more prevalent in Group II (p = 0.017). In both groups, the CSA reduction was statistically significant (Group I = 1°: range 0°-3°, Group II = 3.7°: range 1°-8°; p < 0.001). When the preoperative CSA was > 40°, the respective postoperative CSA remained > 35° in 83.3% of cases (p < 0.001). Final shoulder strength was correlated with the amount of CSA reduction (rho = 0.41, p = 0.002). The postoperative CSA was higher, but not significantly different (n.s.), in patients with re-torn (36°, range 32°-40°) than with healed RC (33°, range 26°-38°). No clinical detachment or hypotrophy of the deltoid was observed with the Akimbo test and ultrasound evaluation.

Conclusions: Arthroscopic lateral acromion resection is a safe procedure without affecting deltoid muscle origin or function, and it is effective in significantly reducing the CSA. However, the CSA cannot always be reduced to < 35°, especially in patients with preoperative CSA values > 40°.

Level Of Evidence: III.