Association of a large lateral extension of the acromion with rotator cuff tears

BACKGROUND: Factors predisposing to tearing of the rotator cuff are poorly understood. We have observed that the acromion of patients with a rotator cuff tear very often appears large on anteroposterior radiographs or during surgery. The purpose of this study was to quantify the lateral extension of the acromion in patients with a full-thickness rotator cuff tear and in patients with an intact rotator cuff. METHODS: The lateral extension of the acromion was assessed on true anteroposterior radiographs made with the arm in neutral rotation. The distance from the glenoid plane to the lateral border of the acromion was divided by the distance from the glenoid plane to the lateral aspect of the humeral head to calculate the acromion index. This index was determined in a group of 102 patients (average age, 65.0 years) with a proven full-thickness rotator cuff tear, in an age and gender-matched group of forty-seven patients (average age, 63.7 years) with osteoarthritis of the shoulder and an intact rotator cuff, and in an age and gender-matched control group of seventy volunteers (average age, 64.4 years) with an intact rotator cuff as demonstrated by ultrasonography. RESULTS: The average acromion index (and standard deviation) was 0.73 +/- 0.06 in the shoulders with a full-thickness tear, 0.60 +/- 0.08 in those with osteoarthritis and an intact rotator cuff, and 0.64 +/- 0.06 in the asymptomatic, normal shoulders with an intact rotator cuff. The difference between the index in the shoulders with a full-thickness supraspinatus tear and the index in those with an intact rotator cuff was highly significant (p < 0.0001). CONCLUSIONS: A large lateral extension of the acromion appears to be associated with full-thickness tearing of the rotator cuff.

Is the lateral extension of the acromion related to the outcome of shoulder injections?

OBJECTIVE To assess patients' outcomes after subacromial or glenohumeral injections based on the degree of lateral extension of the acromion. METHODS 307 patients were prospectively included after therapeutic fluoroscopy-guided subacromial (n = 148) or glenohumeral (n = 159) injections with anaesthetic and long-acting corticosteroids. Pre- and post-injection outcomes at 1 week and 1 month were obtained using the 11-point numerical rating scale (NRS) for pain. Lateral extension of the acromion was quantified and categorized by the critical shoulder angle (CSA) and the acromion index (AI) on anteroposterior conventional radiographs. RESULTS Patients' outcomes at 1 week and 1 month were significantly improved (p < 0.001) compared to baseline for subacromial and glenohumeral injection patients. Patients with a CSA <35° showed significantly higher pain reduction 1 month after subacromial injection compared to patients with a CSA >35° (4.2 ± 2.6 vs. 3.2 ± 3.0, p = 0.04). A significant difference in the 1-month NRS change in pain scores is noted for smaller AIs after subacromial injection (4.3 ± 2.8 vs. 2.6 ± 2.9; p = 0.01). No significant association was noted between clinical outcome and the lateral extension of the acromion after glenohumeral joint injections. CONCLUSIONS A short lateral extension of the acromion was associated with better clinical outcomes in subacromial injection patients but not in glenohumeral injection patients. KEY POINTS • Patients' outcomes at 1 month improved significantly compared to baseline for subacromial injections. • Patients' outcomes at 1 month improved significantly compared to baseline for glenohumeral injections. • Short acromial lateralization was associated with better clinical outcome after subacromial injection. • The acromial lateralization was not associated with clinical outcome after glenohumeral injection.