Association between acromial index and outcomes following arthroscopic repair of full-thickness rotator cuff tears.

BACKGROUND: The purposes of this study were to evaluate the association between the acromial index and full-thickness rotator cuffs and to determine if the size of the acromial index was associated with outcomes in a cohort of patients who had had arthroscopic repair of full-thickness rotator cuff tears.
METHODS: The acromial index was calculated for three groups by individual researchers: 115 patients (120 shoulders) who had arthroscopically repaired full-thickness rotator cuff tears without osteoarthritis (Group I); sixty-four patients (sixty-eight shoulders) who had intact rotator cuffs with osteoarthritis (Group II); and twenty-one patients (twenty-one shoulders) who had intact rotator cuffs, without osteoarthritis, and were managed for other pathology (Group III). The acromial index is the distance between the glenoid plane and the lateral border of the acromion divided by the distance between the glenoid plane and the lateral aspect of the humeral head. Ninety-two patients (ninety-three shoulders) from Group I met inclusion criteria for subjective follow-up. Minimum two-year subjective data were obtained on 86% (seventy-nine patients [eighty shoulders]) of these ninety-two patients to determine the association of the acromial index on surgical outcomes. Surgical factors were also analyzed. Significance was set at p < 0.05.
RESULTS: The acromial index demonstrated high intraobserver agreement (kappa, 0.960; 95% confidence interval, 0.940 to 0.984) and high interobserver agreement (kappa, 0.960; 95% confidence interval, 0.922 to 0.979). The mean acromial index (and standard deviation) was 0.687 ± 0.08 for Group I, 0.685 ± 0.11 for Group II, and 0.694 ± 0.07 for Group III. No significant differences were found. At an average duration of follow-up of 3.0 years (range, 2.0 to 5.4 years), the mean American Shoulder and Elbow Surgeons scores improved from 59 to 93 points (p = 0.001) in the seventy-nine patients from Group I who had minimum two-year duration of subjective follow-up. The mean postoperative scores were 10.4 points (range, 0 to 54.5 points) for the Quick Disabilities of the Arm, Shoulder and Hand Outcome Measure and 9.2 points (on a scale of 1 to 10 points) for patient satisfaction. When the patients with a large acromial index (>0.682) were compared with those with a small acromial index (≤ 0.682), the patients in the former group had a greater likelihood of having a tear involving two or more rotator cuff tendons (p = 0.017), required more anchors to achieve repair (p = 0.007), had slightly lower patient satisfaction scores (mean, 8.9 compared with 9.5 points; p = 0.055) and Short Form-12 Physical Component Summary scores (mean, 49.1 compared with 55.2 points; p = 0.04), and had higher Quick Disabilities of the Arm, Shoulder and Hand scores (mean, 12.9 compared with 7.4 points; p = 0.042).
CONCLUSIONS: An association between the size of the acromial index and that of full-thickness rotator cuff tears was not confirmed; however, a larger acromial index was associated with an increased number of tendons torn and anchors used for repair. In addition, patients with a larger acromial index had more disability as recorded by the Quick Disabilities of the Arm, Shoulder and Hand Outcome Measure and poorer physical health as measured by the Short Form-12 Physical Component Summary score.