Predicting bursal-side supraspinatus tendon tears with the acromioclavicular angle.

Background: Bursal-side supraspinatus tendon tears are a common form of rotator cuff injury, often associated with acromial impingement and other extrinsic factors. Existing anatomical parameters, such as the lateral acromion angle, acromial index, and critical shoulder angle, have been studied in relation to rotator cuff tears; however, reliable indicators specific to the risk of bursal-side supraspinatus tears remain lacking. The acromioclavicular (AC) angle, which reflects the angular relationship between the acromion and clavicle, may offer a new predictive marker for this specific pathology. Methods: In this retrospective case-control study, patients presenting with shoulder pain between January 2016 and February 2020 were reviewed. Group 1 included patients with isolated bursal-side supraspinatus tendon tears confirmed by arthroscopy, while Group 2 consisted of age- and gender-matched controls without rotator cuff pathology. The AC angle was measured using both X-ray and MRI. Diagnostic performance was assessed through Receiver Operating Characteristic (ROC) curve analysis, identifying the optimal cut-point with Youden's index. Reliability was measured using the Intraclass Correlation Coefficient (ICC) for both intra- and inter-rater reliability. Results: The ROC analysis determined an optimal AC angle cut-point of ≤160°. X-ray measurements showed moderate diagnostic value (AUC 0.60, sensitivity 67.2 %, specificity 51.7 %), while MRI measurements demonstrated good diagnostic performance (AUC 0.79, sensitivity 84.5 %, specificity 70.7 %). X-ray yielded high sensitivity but low specificity, suggesting its utility as an initial screening tool, whereas MRI provided improved diagnostic accuracy. Reliability assessments indicated high intra- and inter-rater reliability for AC angle measurements across both imaging modalities (ICC >0.80). Conclusion: The AC angle, particularly when measured on MRI, may serve as a valuable diagnostic marker for identifying isolated bursal-side supraspinatus tendon tears. While X-ray can be utilized as an accessible screening tool, combining it with clinical assessments and MRI is recommended for greater diagnostic precision. Further multi-center, prospective studies are warranted to confirm the clinical utility of the AC angle in predicting rotator cuff pathology.