Determining the Minimal Clinically Important Difference on the Oxford Shoulder Instability Score in Patients Undergoing Arthroscopic Bankart Repair for Shoulder Instability

BACKGROUND: The literature on minimal clinically important differences (MCIDs) for patient-reported outcome measures assessing shoulder instability is limited, with none addressing the Oxford Shoulder Instability Score (OSIS). The OSIS was developed to provide a standardized method for assessing shoulder function after surgery for shoulder instability, and previous studies have demonstrated its high reliability, low interrater variability, and ease of administration. PURPOSE: To identify the MCID for the OSIS after arthroscopic Bankart repair for recurrent shoulder instability. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: A longitudinally maintained institutional registry was queried for patients who underwent arthroscopic Bankart repair from 2010 to 2016 for recurrent shoulder instability secondary to a Bankart lesion without significant glenoid bone loss. The OSIS was completed preoperatively and at 1 year postoperatively. Patients were categorized into “expectations met” and “expectations unmet” groups using a questionnaire evaluating expectation fulfilment. The MCID of the OSIS at 1 year was calculated using 3 anchor-based approaches and a distribution-based approach. The 3 anchor-based approaches comprised (1) simple linear regression analysis, (2) receiver operating characteristic curve analysis, and (3) calculation of mean differences in change for the OSIS between the “expectations met” and “expectations unmet” groups. RESULTS: The study cohort comprised 68 men and 11 women aged 29.9 ± 12.7 years (mean ± SD). Duration of follow-up for all patients exceeded 1 year. The MCIDs for the OSIS based on the 4 calculation approaches yielded a narrow range of values, ranging from 7.7 to 8.5 for the anchor-based methods and 8.6 for the distribution-based method. CONCLUSION: Study results indicated that patients with recurrent shoulder instability without significant bone loss who undergo primary arthroscopic Bankart repair and have at least 8.6 points of improvement on their OSIS experience a clinically significant change at 1 year postoperatively.