Correlation of Glenoid Concavity With Surgical Failure After Arthroscopic Stabilization for Recurrent Anterior Shoulder Instability

Background: Glenoid concavity compression by rotator cuff muscle contraction is one of the key mechanisms in the stability of the glenohumeral joint. Purpose/Hypothesis: The purpose of this study was to evaluate the effects of glenoid concavity, as represented by the bony shoulder stability ratio (BSSR) and other factors, including glenoid bone defect size, on the surgical failure of arthroscopic stabilization procedures for recurrent anterior shoulder instability. The authors also aimed to determine the critical value of BSSR. It was hypothesized that both glenoid concavity and glenoid bone defect size would be correlated with surgical failure, with glenoid concavity having a stronger correlation. Study Design: Case-control study; Level of evidence, 3. Methods: A total of 120 patients who underwent arthroscopic stabilization procedures for recurrent anterior shoulder instability were included. Patients with bony Bankart lesions were excluded to eliminate the postoperative effects of bony fragment restoration on the glenoid concavity. For each patient, variable factors including BSSR, glenoid bone defect size, presence of off-track Hill-Sachs lesions, and age at first dislocation were recorded. Chi-square analysis and Student t test were performed to analyze the effect of each variable on surgical failure. Multivariate logistic regression analysis was used to determine the combined effect of >2 variables on surgical failure. The critical value of BSSR was analyzed using a receiver operating characteristic curve. Results: Nine patients (7.5%) had recurrent instability requiring revision surgery. BSSR (patients with recurrence, 18.6% ± 19.4%; patients without recurrence, 41.8% ± 10.5%; P = .01), glenoid bone defect size (17.5% ± 3.6% vs 11.7% ± 7.0%; P = .02), age at the time of first dislocation (18.8 ± 3.9 years vs 22.0 ± 6.5 years; P = .04), and number of suture anchors used (4.1 ± 0.3 vs 5.8 ± 1.6; P < .001) showed significant differences between patients with and without surgical failure. Multivariate logistic regression analysis revealed surgical failure to be correlated with BSSR (odds ratio, 0.849; P = .02) and the number of suture anchors used (odds ratio, 0.070; P = .03). The critical value of BSSR was 29.3% (area under the curve, 0.84; 95% CI, 0.67-1.00; P < .001; sensitivity, 78%; specificity, 93%). Conclusion: Glenoid concavity is strongly correlated with surgical failure after arthroscopic stabilization procedures for anterior shoulder instability. The value of BSSR reflects shoulder instability caused by glenoid bone morphology more accurately than glenoid bone defect size.