Site-specific biomechanical alterations of the knee during gait in ACL-deficient patients with concomitant cartilage lesions

Background Anterior cruciate ligament (ACL) deficiency often coexists with articular cartilage damage, yet the biomechanical effects of lesion location on knee kinematics during gait remain unclear. This study investigated the association between cartilage lesion site and six degrees of freedom (6-DOF) knee kinematics in ACL-deficient knees. Methods A total of 116 patients with unilateral ACL deficiency were divided into four groups: isolated ACL deficiency (ACLDI), ACL with femoral cartilage lesion (ACLDF), ACL with tibial cartilage lesion (ACLDT), and ACL with combined femoral–tibial lesions (ACLDC). Three-dimensional motion capture was used to record knee 6-DOF kinematics during walking. One-way ANOVA and Statistical Parametric Mapping (SPM1d) were applied to identify intergroup differences. Key discrete gait parameters were further reanalyzed using meniscal-adjusted linear models. Results Meniscal-adjusted analyses indicated that group differences remained in selected gait parameters. Specifically, differences were identified in the abduction–adduction, flexion–extension, and anterior–posterior displacement dimensions. Compared with the ACLDI group, ACLDT and ACLDC patients exhibited greater adduction and anterior tibial translation during the stance phase, while ACLDF and ACLDC showed reduced knee flexion and overall range of motion. Conclusion In ACL-deficient knees, gait biomechanical alterations are associated with cartilage lesion location. Different lesion locations appear to correspond to distinct functional phenotypes, suggesting that lesion-specific assessment may improve identification of residual instability and inform more individualized rehabilitation strategies to restore joint stability and reduce the risk of secondary degeneration.