Critical shoulder angle (CSA) is the angle between glenoid inclination and the lateral edge of the acromion. CSA>35° has been shown to be a risk factor for primary and iterative rotator cuff tendon tear. The present study aimed to assess change in CSA after anterior acromioplasty. The study hypothesis was that CSA is significantly reduced.

A single-center retrospective descriptive observational study included patients undergoing open or arthroscopic anterior acromioplasty, with strict AP pre- and post-operative radiographs. Patients with radiographs not meeting Moor's criteria were excluded.

One hundred and forty-eight patients were included: arthroscopy, 112; open surgery, 36. Mean age was 57.8 years (range, 29–80 years). Mean preoperative CSA was 36.1±4.25° (range, 25–48.4°) and postoperative CSA 33.5±3.9° (23.8–45.2°), for a significant reduction of −2.6±2.5° (p=0.001). Surgical technique did not affect change in CSA: open surgery, −2.3±1.9° (−6.3° to −1°); arthroscopy, −2.7±2.7° (−10.5° to −5°) (p=0.06). In pathologic CSA (>35°), the mean reduction was −3.2±2.6° (−10.5°to −5°). CSA normalized below the 35° threshold in 48% of patients.

Despite reduction in CSA, the 35° threshold for iterative tear is not always reached after anterior acromioplasty. Complementary strictly lateral resection is theoretically required. However, change in CSA is difficult to predict intraoperatively.

Anterior acromioplasty significantly reduced CSA, independently of technique and preoperative value.

IV, retrospective descriptive study.