Low Fragility Index Undermines Confidence in ACL Graft Superiority: A Systematic Review and Fragility Index Analysis

Abstract

Background:

Graft selection is a key factor in anterior cruciate ligament reconstruction (ACLR), yet the statistical robustness of comparative outcomes remains unclear. Reliance on P values may overstate confidence in clinical differences.

Purpose:

To assess the statistical fragility of dichotomous outcomes in randomized controlled trials (RCTs) comparing hamstring tendon (HT), bone–patellar tendon–bone (BPTB), quadriceps tendon (QT), and allograft ACL grafts.

Study Design:

Systematic review and fragility analysis; Level of evidence, 1.

Methods:

A systematic search of PubMed, Embase, and Medline (June 2025) identified RCTs comparing 2 ACL graft types with >1 dichotomous outcome. Outcomes were analyzed for fragility index (FI), reverse FI (rFI), fragility quotient (FQ), and reverse FQ (rFQ); those with zero events in both groups were excluded. Median FI and rFI values were compared across graft types and outcome categories, and significant outcomes were stratified by graft type.

Results:

A total of 29 RCTs (200 outcomes) were included; 179 outcomes (89.5%) were analyzed, and 21 (10.5%) showed significant results. Overall median FI and rFI were both 2.0 (interquartile range: FI 1.0-5.0, rFI 1.0-4.0). In 26 studies (89.7%), loss to follow-up exceeded or equaled the FI or rFI. HT versus BPTB was the most common graft pair comparison (72.1%). All graft comparisons had high fragility (FI ≤2.5). Radiographic complications and knee complications had relatively high FIs (6.5 and 4.5), whereas medical complications, revision ACL, and secondary surgery were most fragile (FI = 1.0). Among significant outcomes, HT had the highest FQ (0.034), followed by QT (0.026) and BPTB (0.016); none favored allografts.

Conclusion:

Many ACLR RCT findings were fragile, with most significant results reversible by altering 2 events. Loss to follow-up often exceeded fragility thresholds, raising reliability concerns. Although HT had the greatest number of significant outcomes and highest FQ, this likely reflects study volume rather than clinical superiority. High-powered RCTs with standardized outcomes and fragility reporting are needed to clarify graft effectiveness.