Minimal important clinical difference values are not uniformly valid in the active duty military population recovering from shoulder surgery

Background: There are multiple methods for calculating the minimal clinically important difference (MCID) threshold, and previous reports highlight heterogeneity and limitations of anchor-based and distribution-based analyses. The Warfighter Readiness Survey assesses the perception of a military population's fitness to deploy and may be used as a functional index in anchor-based MCID calculations. The purpose of the current study in a physically demanding population undergoing shoulder surgery was to compare the yields of 2 different anchor-based methods of calculating MCID for a battery of PROMs, a standard receiver operating characteristic (ROC) curve-based MCIDs and baseline-adjusted ROC curve MCIDs.

Methods: All service members enrolled prospectively in a multicenter database with prior shoulder surgery that completed pre- and postoperative PROMs at a minimum of 12 months were included. The PROM battery included Single Assessment Numeric Evaluation (SANE), American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES), Patient Reported Outcome Management Information System (PROMIS) physical function (PF), PROMIS pain interference (PI), and the Warfighter Readiness Survey. Standard anchor-based and baseline-adjusted ROC curve MCIDs were employed to determine if the calculated MCIDs were both statistically and theoretically valid (95% confidence interval [CI] either completely negative or positive).

Results: A total of 117 patients (136 operations) were identified, comprising 83% males with a mean age of 35.7 ± 10.4 years and 47% arthroscopic labral repair/capsulorrhaphy. Using the standard, anchor-based ROC curve MCID calculation, the area under the curve (AUC) for SANE, ASES, PROMIS PF, and PROMIS PI were greater than 0.5 (statistically valid). For ASES, PROMIS PF, and PROMIS PI, the calculated MCID 95% CI all crossed 0 (theoretically invalid). Using the baseline-adjusted ROC curve MCID calculation, the MCID estimates for SANE, ASES, and PROMIS PI were both statistically and theoretically valid if the baseline score was less than 70.5, 69, and 65.7.

Conclusion: When MCIDs were calculated and anchored to the results of standard, anchor-based MCID, a standard ROC curve analysis did not yield statistically or theoretically valid results across a battery of PROMs commonly used to assess outcomes after shoulder surgery in the active duty military population. Conversely, a baseline-adjusted ROC curve method was more effective at discerning changes across a battery of PROMs among the same cohort.