The Nonoperative Instability Severity Index Score (NISIS): A Simple Tool to Guide Operative Versus Nonoperative Treatment of the Unstable Shoulder

Background: The management of the adolescent athlete after initial shoulder instability remains controversial. Hypothesis: Individual risk factors in athletes with shoulder instability who are managed nonoperatively can be integrated into a scoring system that can predict successful return to sport. Study Design: Retrospective cohort study. Level of Evidence: Level 4. Methods: A total of 57 scholastic athletes with primary anterior shoulder instability who were managed nonoperatively were reviewed. Success was defined as a return to index sport at the same level and playing at least 1 subsequent season without missed time as a result of the shoulder. Patient-specific risk factors were individually evaluated, and odds ratios were calculated. A 10-point Nonoperative Injury Severity Index Score (NISIS) incorporated the risk factors for failure. This score was then retrospectively applied with regression analysis and a chi-square analysis to determine the overall optimal score that predicted failure of nonoperative management. Results: In total, 6 risk factors for failure were included in the NISIS: age (>15 years), bone loss, type of instability, type of sport (contact vs noncontact), male sex, and arm dominance. Overall, 79% of patients treated nonoperatively were able to successfully return to sport. Nearly all (97%) low-risk patients (NISIS <7) successfully returned to sport, while only 59% of high-risk patients returned to sport, a relative risk of 12.2 (P = 0.001). High-risk patients with unipolar bone loss successfully returned (100%), but 67% of high-risk patients with bipolar bone loss failed. Conclusion: The NISIS is a simple and effective clinical tool to determine successful nonoperative management following anterior shoulder instability and may be helpful in guiding decision making when presented with the unstable shoulder in the scholastic athlete.