Gait Biomechanical Differences in the Anterior Cruciate Ligament Reconstructed and Contralateral Limb: A Systematic Review with Meta-Analysis

Background: In this systematic review with meta-analysis, we aimed to compare the kinematic and kinetic variables of the involved limb with the contralateral limb in individuals who had undergone an anterior cruciate ligament reconstruction (ACLR) recorded during walking from short-term (<6 months) to mid-term (6–<12 months) and long-term (≥12 months) periods after surgery. Methods: Five electronic databases (Scopus, PubMed, EMBASE, PEDro, CENTRAL) were systematically searched for articles potentially eligible for inclusion from inception until November 2025. Biomechanical gait patterns were assessed short-term (<6 months), mid-term (6–<12 months), and long-term (≥12 months) post-surgery. Gait biomechanics were extracted from the included articles. Comparisons were made between the affected limb and the contralateral limb. Standardized mean differences (SMDs) with 95% confidence intervals (CI) were computed using a random-effects model. Results: The systematic search revealed 3522 hits, and according to a priori defined in-/exclusion criteria, 32 studies with male and female individuals aged 18–55 years involving 1026 participants were included. Meta-analysis indicated that the peak knee flexion angle was significantly lower in the ACLR compared to the contralateral limb (19 studies: small SMDs = −0.39, 95% CI −0.58 to −0.19, p < 0.0001, I² = 66%). More specifically, the peak knee flexion angle was 2.63° (95% CI -3.81 to -1.44) lower in the ACLR compared to the contralateral limb. The analysis of time post-surgery revealed significant differences in the short-term (four studies: large SMDs = −1.14, 95% CI −1.61 to −0.67, p < 0.00001, I² = 56%) and mid-term (five studies: small SMDs = −0.52, 95% CI −0.74 to −0.29, p < 0.0001, I² = 0%) periods after surgery but not for the long-term follow-up (10 studies: small SMDs = −0.10, 95% CI −0.27 to 0.07, p = 0.26, I² = 32%). Meta-analysis indicated that the peak knee flexion moment was significantly lower in the ACLR compared to the contralateral limb (11 studies: small SMDs = −0.37, 95% CI −0.59 to −0.14, p = 0.0001, I² = 46%). A lower peak knee flexion moment was observed in the ACLR limb for both less than 12 months (three studies: moderate SMDs = −0.76, 95% CI −1.44 to −0.07, p = 0.03, I² = 66%) and over 12 months (eight studies: small SMDs = −0.25, 95% CI −0.43 to −0.07, p = 0.01, I² = 46%) after surgery time points compared to the contralateral limb. Conclusion: These findings suggest a time-dependent compensatory mechanism, where protective adaptations (e.g., reduced flexion/extension moments) may initially offload the reconstructed limb, with some asymmetries resolving over time. Clinically, these results underscore the need for rehabilitation strategies tailored to address phase-specific deficits, promoting symmetrical loading and functional recovery.