DO RUNNING BIOMECHANICS NORMALIZE AFTER ACL RECONSTRUCTION? A SYSTEMATIC REVIEW AND META-ANALYSIS ACROSS POST-OPERATIVE PHASES

Abstract

Background: Altered running biomechanics following anterior cruciate ligament reconstruction (ACLR) have been implicated in impaired performance, increased risk of re-injury, and early knee osteoarthritis. A landmark systematic review published in 2019 identified persistent sagittal-plane deficits during running after ACLR; however, substantial biomechanical evidence has emerged since then. Objective: To systematically review and synthesize evidence published through 2025 on running biomechanics after ACLR, with particular emphasis on temporal changes in kinematic, kinetic, and muscle activation patterns across post-operative phases. Methods: A systematic review was conducted in accordance with PRISMA guidelines. MEDLINE, EMBASE, SPORTDiscus, and CINAHL were searched from inception to December 2025. Observational studies assessing running kinematics, kinetics, or muscle activation in individuals following ACLR were included. Outcomes were stratified by time since surgery: early (<6 months), mid (6–12 months), intermediate (12–24 months), and long-term (>24 months). Where appropriate, meta-analyses were performed using standardized mean differences. Risk of bias was assessed using a modified Downs and Black checklist, and levels of evidence were determined based on methodological quality and consistency. Results: Fifty-four studies comprising 1,248 individuals with ACLR were included. Strong evidence demonstrated reduced peak knee flexion angle, knee flexion excursion, and internal knee extension moment during running in the reconstructed limb compared with contralateral and control limbs across all time periods. Although gradual improvement was observed over time, small but significant deficits persisted beyond two years post-surgery. Ground reaction force measures showed conflicting results, while joint contact forces exhibited limited but consistent alterations, particularly at mid-term follow-up. Muscle activation patterns were largely similar between limbs. Quadriceps and hamstring strength asymmetries and self-reported knee function were associated with altered running biomechanics, whereas surgical technique showed minimal influence. Conclusion: Running biomechanics after ACLR demonstrate partial recovery over time but do not fully normalize, with persistent sagittal-plane deficits evident long term. Targeted neuromuscular and strengthening interventions may be required to optimize running mechanics and support long-term joint health following ACL reconstruction.