Objectives:There has been a hesitation by surgeons to operate on shoulder instability patients with maladaptive psychopathological traits, especially those with volitional instability, as these may portend a poor prognosis. The purpose of this study was to investigate the prevalence of maladaptive psychopathological traits, volitional instability, and their effect on two-year outcomes in patients undergoing shoulder stabilization surgery.Methods:A prospective multi-center cohort study led by the Multicenter Orthopaedic Outcomes Network (MOON) Shoulder Group targeted all subjects having surgical shoulder stabilization and collected patient-reported outcomes at baseline and at two years postoperatively. Psychopathological traits were assessed using the Personality Assessment Screener (PAS), a validated personality assessment tool. Longitudinal analyses were performed using multivariable regression models to determine predictors of two-year outcomes adjusting for confounders measured at index such as age, sex, smoking, BMI, volitional instability, and intraarticular pathology.Results:The cohort (n = 890) was 80% male with a median age of 21.5 years. The prevalence of psychopathological traits was 20%. While all patients improved between baseline and 2 years, with adjusted analyses, the presence of maladaptive psychological traits present at the time of index surgery were predictive of lower WOSI (p = 0.001), ASES (p = 0.016), SANE (p = 0.03), and SF-36 MCS (p = 0.001) scores as well as a higher risk of failure (p = 0.04) at two years. As a main effect, volitional instability was not a predictor of WOSI, ASES, SANE, SF-36 or failure at two years. However, all models allowed for the interaction between volitional instability and the PAS, and this interaction was significant for WOSI (p = 0.006), SANE (p = 0.03), and SF-36 MCS (p = 0.003) scores at two years. In other words, the effect of volitional instability on the WOSI, SANE, and SF-36 MCS scores depends on the value of the PAS, and with high PAS scores it is associated with worse outcomes. This data is depicted in Figures 1-3.Conclusions:While all patients improved, the presence of maladaptive psychopathological traits at the time of index surgery was a predictor of poorer outcomes at two years. Voluntary dislocators did similarly as non-voluntary dislocators up to a PAS score of ˜ 20, where above this they had worse WOSI, SANE, SF-36 MCS and higher failure rates at 2 years post-operatively.Figure 1.Adjusted effects of PAS score and volitional instability on WOSI score at 2 yearsFigure 2.Adjusted effects of PAS score and volitional instability by gender on predicted MCS Score at two yearsFigure 3.Adjusted effects of PAS score and volitional instability on probability of failure