The Statistical Fragility of Treatments for Adhesive Capsulitis: A Systematic Review of Randomized Controlled Trials.

Introduction: Randomized controlled trials (RCTs) have assessed a range of treatments for shoulder adhesive capsulitis (AC), with conflicting results over the most clinically beneficial options. This study used the fragility index (FI), reverse fragility index (rFI), and fragility quotient (FQ) to evaluate statistical fragility of the outcomes reported in RCTs assessing the efficacy of shoulder AC treatments.

Methods: PubMed and Embase were systematically searched for RCTs from January 1, 2004, to May 1, 2024 that assessed shoulder AC treatments. We quantified FI and rFI, which represent the amount of outcome event reversals necessary to change statistical significance for significant and non-significant findings, respectively. Subanalyses were performed for outcomes relating to clinical efficacy, patient satisfaction, pain, and adverse events. The FQ was determined by dividing the FI by the study sample size.

Results: Of 468 articles screened, there were a total of 38 RCTs analyzed that yielded 67 outcomes of interest. Across the 67 outcomes, the median FI was 3 (IQR [Interquartile Range] 2-6) and the median FQ was 0.075 (IQR 0.034-0.100). The 17 statistically significant outcomes had a median FI of 2 (IQR 1-4) and a median FQ of 0.050 (IQR 0.018-0.091). The remaining 50 outcomes were statistically nonsignificant, with a median FI of 4 (IQR 2-6) and a median FQ of 0.079 (IQR 0.037-0.102). Notably, in 40.3% of all outcomes, loss-to-follow-up was greater or equal to the outcome's respective FI or rFI. The most fragile outcomes were related to patient satisfaction (FI 2) and adverse events (FI 2.5).

Conclusion: The outcomes of interest regarding treatments for adhesive capsulitis from RCTs are statistically fragile, most notably significant outcomes and those pertaining to patient satisfaction. RCT results surrounding adhesive capsulitis treatments remain inconclusive; thus, combining p-values with both FI and FQ metrics may improve the interpretation of clinical findings regarding treatment modalities for adhesive capsulitis. Future clinical RCTs may reduce outcome fragility by improving follow-up rates and increasing patient sample sizes.