Is the Instability Severity Index Score a Valid Tool for Predicting Failure After Primary Arthroscopic Stabilization for Anterior Glenohumeral Instability?

PURPOSE: To assess the validity of the Instability Severity Index Score in predicting the rate of recurrence of dislocation in patients undergoing arthroscopic Bankart repair.

METHODS: The inclusion criteria were recurrent anterior traumatic glenohumeral instability and a minimum follow-up of 5 years. According to the preoperative Instability Severity Index Score, patients were divided into the following groups: ≤3 points (A), 4 to 6 points (B), and >6 points (C). The recurrence rate was determined by telephone interviews. The estimated overall rate of success at 5 years was defined as the estimated overall percentage of patients free of recurrence at 5 years.

RESULTS: Six hundred seventy patients (572 men and 98 women) were included. The average age was 27 years (range, 18 to 39 years) at the time of surgery. One hundred fourteen of 670 patients had a recurrence of instability, with an overall recurrence rate of 17% (95% confidence interval [CI] 14.2%-19.9%). The Instability Severity Index Score had a significant association with recurrence. Compared with patients in group A, those in group B had double the risk of recurrence (hazard ratio [HR] = 2.43, 95% CI 1.38-4.28, P = .002), and patients in group C a 9 times greater risk of recurrence (HR = 9.42, 95% CI 5.20-17.7, P < .001). The estimated overall rate of success at 5 years was 84.8% (95% CI 81.8-87.3). The rate of success with an Instability Severity Index Score ≤3 points was 93.7% (95% CI 89.6-96.2), but it dropped to 85.7% (95% CI 81.7-88.9) in those with an Instability Severity Index Score of 4 to 6 points and became 54.6% (95% CI 42.8-64.9) in those with an Instability Severity Index Score >6 points. On multivariable analysis, the Instability Severity Index Score was found to significantly affect the risk of recurrence, corrected by type of sport and glenoid bone loss.

CONCLUSIONS: The Instability Severity Index Score is a validated tool with which to assess the recurrence rate of dislocation after arthroscopic surgery in patients with shoulder instability. Arthroscopic stabilization in patients with an Instability Severity Index Score ≤3 is associated with a significantly lower risk of recurrence of glenohumeral instability compared with that in patients with an Instability Severity Index Score >3 points.

LEVEL OF EVIDENCE: III, case-control study.