The Nonoperative Instability Severity Index Score: Is It Predictive in a Larger Shoulder Instability Population at Long-Term Follow-Up?

Purpose: To evaluate the effect of the Nonoperative Instability Severity Index Score (NISIS) criteria on an established US-geographic population-based cohort of patients with anterior shoulder instability. Methods: An established geographically based medical record system was used to identify patients <40 years of age with anterior shoulder instability between 1994 and 2016. Medical records were reviewed to obtain patient demographics and instability characteristics. Patient-specific risk factors were individually incorporated into the 10-point NISIS criteria: age (>15 years), bone loss, type of instability (dislocation vs subluxation), type of sport (collision vs noncollision), male sex, and dominant arm involvement. High risk was considered a score of ≥7 points and low risk as <7 points. Failure was defined as either progression to surgery or recurrent instability diagnosed by a consulting physician at any point after initial consultation. Results: The study population consisted of 405 patients with a mean follow-up time of 9.6 ± 5.9 years. Failure was defined as recurrent instability or progression to surgery, and the overall failure rate was 52.8% (214/405). The rate of recurrent instability after initial consultation was 34.6% (140/405), and the rate of conversion to surgery was 37.8% (153/405). A total of 264 (65.2%) patients were considered low risk (NISIS < 7), and 141 (34.8%) patients were considered high risk (NISIS ≥ 7). Patients in the high-risk group were more likely to fail nonoperative management than those in the low-risk group (60.3% vs 48.9%; P = .028). Conclusions: The NISIS has been proposed as a potentially useful tool in clinical decision-making regarding the appropriate use of nonoperative treatment in scholastic athletes. When applied to an established US-geographic population-based cohort consisting of competitive and recreational athletes under the age of 40 with longer-term follow-up, the NISIS high-risk cutoff was able to predict overall failure with 60.3% accuracy.