Interventional therapies for subacromial impingement syndrome: A systematic review and fragility analysis of randomized controlled trials.

Introduction: Interventional therapies for subacromial impingement investigated by randomized controlled trials (RCTs) yield conflicting results and overemphasize p-values, with some studies indicating efficacy and others showing no clinical significance. To assess the statistical robustness of these findings, the fragility index (FI), reverse fragility index (rFI), and fragility quotient (FQ) were utilized in the analysis of RCTs examining interventional therapies in the context of subacromial impingement. Methods: From January 1, 2000 to July 1, 2024, PubMed, Embase, and MEDLINE were systematically searched for RCTs or comparative trials that evaluated outcomes for patients with Subacromial Impingement. Of 300 studies screened, 38 RCTs were included for analysis. We calculated the FI and rFI to determine the number of event reversals needed to alter statistical significance. The FQ was then derived by dividing the FI by the study's sample size. Results: Across 150 outcomes, the median FI was 4 (IQR 3-6) with a median FQ of 0.061 (IQR 0.026-0.100), suggesting that just three outcome event reversals would alter significance. Of these, 31 outcomes were statistically significant also with a median FI of 4 (IQR 2-6) and FQ of 0.066 (IQR 0.033-0.099), while 119 outcomes were nonsignificant with a median rFI of 4 (IQR 3-6) and FQ of 0.060 (IQR 0.025-0.100). Notably, the number of patients lost to follow-up was greater than the outcome's respective FI or rFI in 39.4 % of all outcomes. Conclusion: The efficacy of interventional therapies for subacromial impingement from RCTs is statistically fragile, particularly significant outcomes and studies with a high proportion of patients lost to follow-up. We recommend combined reporting of p-values with FI and FQ metrics to aid in interpreting clinical findings evaluating interventional therapies for subacromial impingement. Future studies may mitigate outcome fragility by obtaining higher follow-up rates and study sample sizes.