Foot and Ankle Contributions to Noncontact ACL Injury Risk: A Systematic Review.

Background: Noncontact anterior cruciate ligament (ACL) injuries are common and carry long-term consequences for the athlete. Altered foot and ankle biomechanics, landing patterns, and prior ankle injury have been implicated in ACL injury risk and may inform prevention strategies. Purpose: To identify key biomechanical risk factors associated with the foot and ankle that may contribute to ACL injury risk. Study Design: Systematic review; Level of evidence, 4. Methods: A systematic review was conducted following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) 2020 guidelines. PubMed, Cochrane, and SPORTDiscus databases were searched for English-language studies (2010-2025) evaluating ACL injuries and reporting on the foot or ankle. Screening was performed using Rayyan, followed by full-text review. Data were extracted, and then risk of bias was assessed using the methodological index for non-randomized studies (MINORS). Results: Out of 1772 studies evaluated, a total of 48 (2.7%) studies met inclusion criteria. Overall, 33 studies (68.8%) identified variables associated with increased ACL injury risk, while 11 (22.9%) reported decreased risk and 9 (18.8%) found no association. Foot and ankle biomechanics were examined in 32 studies (66.7%), foot strike pattern in 8 (16.7%), toe direction in 7 (14.6%), and prior ankle injury history in 5 (10.4%). Statistically supported findings were present in 81% of studies. Greater dynamic rearfoot motion (eversion/inversion), increased dorsiflexion, and medial arch collapse (eg, navicular drop) were commonly associated with increased risk. Forefoot landings were protective, while rearfoot and flatfoot strikes, as well as toe-in or toe-out positions, were consistently linked to higher injury risk. Sex-specific analysis showed that female athletes demonstrated more high-risk biomechanical patterns than their male counterparts. Sport-specific analysis revealed basketball (n = 14), soccer (n = 8), and handball (n = 6) as the most studied sports, with >75% of these studies identifying ≥1 foot- or ankle-related ACL injury risk factor. Study quality was generally low, with predominantly noncomparative designs and modest MINORS. Conclusion: Foot and ankle factors, including prior injury, alignment, foot strike patterns, and toe progression, contribute meaningfully to ACL injury risk, yet their precise influence on knee stabilization remains unclear. The foot and ankle are understudied, with few investigations addressing their role in dynamic tasks that challenge knee stability. High-quality comparative research that accounts for sex and sport differences is needed to inform targeted prevention and improve risk stratification.