Factors Affecting Return to Baseline Function at 6 months Following Anterior Shoulder Instability Surgery: A Multi-Center Orthopaedic Outcomes Network (MOON) Shoulder Group Cohort Study

OBJECTIVES: Pre-operative and surgical factors related to early return to baseline function after anterior shoulder instability surgery are not clear. This study was designed to determine the pre-operative and operative factors affecting return to baseline function at 6 months following anterior shoulder instability surgery. Identifying these factors will help surgeons establish expectations for functional return post-operatively. METHODS: The Multicenter Orthopaedic Outcomes Network (MOON) shoulder group enrolled patients undergoing surgery for shoulder instability from 16 sites throughout the United States. Initial demographic data and validated, patient-oriented outcomes questionnaires were collected along with the physicians documented initial physical exam, treatment, surgical findings and surgical techniques used at the time of surgery. At the 6-month follow up visit, range of motion (ROM) and strength measurement of the operative shoulder were collected and compared to pre-operative measurement. Return to baseline was defined as return to within -10° ROM and full strength at the 6 month physical exam. Continuous and categorical data were analyzed using student t-tests and chi-square tests, respectively. The Kruskal-Wallis/Wilcoxin tests were used to compare groups that were not normally distributed. Factors reaching significance in a univariate analysis were then applied in a multivariable model. Significance was set a p<0.05. RESULTS: A total of 338 patients with history of surgical intervention for anterior instability of the shoulder were identified. 278 patients had complete pre- and post-surgical range of motion and strength measurements. 138 (50%) patients (139 shoulders) returned to baseline and 133 (50%) patients did not return to baseline. Univariate analysis identified age (p=0.0013), Beighton score (p=0.0004), SF-36 general health (p=0.0017), WOSI (p=0.0250), and duration of symptoms (p=0.0046) as significant factors. When these factors were placed into a multivariate model, significant differences were identified in age (p=0.0316), SF-36 General health (p=0.0118), and Beighton score (p=0.0016). CONCLUSION: Older age, perception of general health and generalized joint laxity are associated with failure to return to baseline function at 6 months after anterior shoulder instability surgery. Duration of symptoms and number of dislocation events did not reach significance in the multivariate model, but trended toward likelihood of failure to return to baseline findings. Moreover, open vs. arthroscopic surgery and number of suture anchors were not significant, suggesting that pre-operative condition and not surgical factors predict return to baseline in the short-term.