The Fragility of Statistical Findings in Achilles Tendon Injury Research: A Systematic Review

Probability analysis with the reporting of P values is often used to determine the statistical significance of study findings in the Achilles literature. The purpose of this study was to determine the utility of applying a fragility analysis to comparative trials evaluating Achilles tendon injuries. METHODS: We identified all dichotomous outcome data for comparative studies of Achilles tendon injuries published in 11 orthopaedic journals from 2000 to 2020. The fragility index (FI) was determined by the number of event reversals required to change a P value from less than 0.05 to greater than 0.05, or vice-versa. The associated fragility quotient was determined by dividing the FI by the sample size. RESULTS: Of the 51,357 studies screened, 1,487 met the search criteria, with 51 comparative studies and 177 total outcome events included for analysis. The overall FI was only 4 with an associated fragility quotient of 0.048. One-half of the studies failed to report lost to follow-up data, with an additional 21.6% reporting loss to follow-up of greater than or equal to 4. CONCLUSION: Our fragility analysis suggests that Achilles tendon injury outcomes are not as statistically stable as previously thought and should be interpreted with caution.