Simple clinical measures quantify knee loading symmetry during running after anterior cruciate ligament reconstruction

Objectives: Knee loading asymmetry is commonly observed during running after anterior cruciate reconstruction (ACL-R). We sought to determine whether clinically measurable asymmetries could predict knee loading symmetry (LSI) during running after ACL-R. Design: Longitudinal laboratory study. Setting: Three-dimensional running biomechanics. Participants: 24 participants post-ACL-R and 24 healthy, matched controls. Main outcome measures: LSI of knee loading variables (patellofemoral and tibiofemoral joint reaction force [PFJRF/TFJRF], and knee negative work) were assessed alongside clinically measurable variables (stance time, peak knee flexion angle, knee flexion excursion and foot strike angle). Assessments were conducted at baseline (D1) in both groups, with the ACL-R group also assessed after a 14-day return-to-run program (D14). Results: Peak knee flexion angle LSI significantly predicted PFJRF and TFJRF peak and average loading rate LSIs (all p < 0.01). Knee flexion excursion LSI predicted knee negative work LSI (p < 0.001). The R² for the predictive equations for PFJRF Average loading rate, PFJRF Peak, TFJRF Peak, TFJRF Average loading rate and Knee negative work were 0.69, 0.75, 0.73, 0.58 and 0.41, respectively. Conclusions: Knee joint loading symmetry during running following ACL-R can be estimated using clinically accessible variables. Among these, peak knee flexion angle symmetry emerged as the most promising predictor. Level of evidence: Longitudinal observational study, level III.