Are critical shoulder angle and acromion index correlated to the size of a rotator cuff tear.

Purpose: Scapular morphology is an extrinsic factor playing role in rotator cuff tear (RCT) etiology. The objective of this study was to evaluate the relationship between critical shoulder angle (CSA) and acromion index (AI) with partial-bursal side and full thickness RCT and the size of the RCT.

Hypothesis: The hypothesis was that CSA and AI would be greater in partial bursal-side RCT and full-thickness RCT patients and would increase with the size of the RCT.

Methods: This retrospective study assessed 218 patients who had standard shoulder radiographs and magnetic resonance imaging. Patients were divided into three groups: intact rotator cuff (68), partial bursal-side RCT (34) and full-thickness RCT (116). In the second part, full-thickness RCT patients were divided into four groups according to RCT size; small (<1cm), medium (1-3cm), large (3-5cm) and massive (>5cm). AI and CSA measurements were evaluated from radiographs.

Results: The mean CSA was 32.8̊ in control group, 34.3̊ in partial group and 36.9̊ in full-thickness group. The mean AI was 0.66, 0.68 and 0.72 respectively. Significant difference was found in AI and CSA between full thickness RCT and intact RC group (p<0.01), and partial RCT and full thickness RCT group (p<0.05) in paired comparisons. In full thickness RCT size groups the mean CSA was 34.2̊, 36.4̊, 39.0̊ and 40.8̊ and mean AI was 0.70, 0.71, 0.73 and 0.79 respectively. Significant difference was found between small-large, small-massive, medium-massive groups for CSA in paired comparisons and between small-massive, medium-massive groups for AI.

Conclusion: CSA and AI were significantly greater in full-thickness RCT patients and the size of the RCT increased with CSA and AI. The greater CSA and AI could be predictors for larger RCT.

Level Of Evidence: III; Cross-Sectional Design; Prognosis Study.