The Fragility Index of Total Hip Arthroplasty Randomized Control Trials: A Systematic Review

J Am Acad Orthop Surg. 2022 May 1;30(9):e741-e750. doi: 10.5435/JAAOS-D-21-00489. Epub 2022 Feb 24.


Introduction: Although randomized controlled trials (RCTs) are considered the benchmark study design, a change of outcomes for a few patients can lead to a reversal of study conclusions. As such, examination of the fragility index (FI) of RCTs has become an increasingly popular method to provide further information regarding the relative robustness of RCT results. The purpose of this study was to systematically characterize and assess the predictors of the FI RCTs in total hip arthroplasty literature.

Methods: PubMed/MEDLINE, Embase, and Cochrane were systematically searched for all total hip arthroplasty RCTs published between January 2015 and December 2020, which had an equal assignment of participants to a two parallel-arm study design, examined a surgical intervention, and reported on at least one statistically significant dichotomous outcome in the abstract. Potential factors associated with the FI were examined using the Spearman correlation and Mann-Whitney U test.

Results: Thirty-four RCTs were selected, with a median number of study participants of 111 (interquartile range [IQR] 72-171] and a median total number of events of 15 (IQR 9.5 to 29). The median FI was 2 (IQR 1 to 6), while six studies had a FI of 0. In 18 cases (52.9%), the number of patients needed to change from no event to event was less than that loss to follow-up. Larger sample size was found to predictive of a higher FI (rs = 0.367, P = 0.033), but the year of publication, journal impact factor, the calculated power analysis size, and loss to follow-up were not associated with FI.

Conclusion: The FI serves as a useful addition to other more commonly used approaches of quantitative analyses, such as P values, effect sizes, and confidence intervals, and widespread reporting the FI may provide clinicians with further information about RCT results.

Level of evidence: Level I, systematic review of Level I studies.

Publication types

  • Systematic Review

MeSH terms

  • Arthroplasty, Replacement, Hip*
  • Humans
  • Journal Impact Factor
  • Randomized Controlled Trials as Topic
  • Research Design
  • Sample Size