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Although several reports show that altered biomechanics associate with post-traumatic osteoarthritis, it is not fully understood and of great interest whether altered biomechanics associate with meniscal change after ACLR. Hence, the objective of this study is (1) to determine the biomechanics during two different tasks (gait and landing) and meniscal matrix alterations present before and after ACLR and (2) to evaluate associations between biomechanical and biochemical meniscal matrix changes in acute ACL injured knees 3 years after reconstruction. Methods: Thirty-six ACLR patients (male; 20, female; 16, mean age; 31.5 ± 7.6 years, mean time from injury to surgery; 76.7 ± 52.8 days) and fourteen healthy controls (male; 9, female; 5, mean age; 31.4 ± 4.9 years) were included in the study. All patients underwent MRI of the injured and contralateral knees, and biomechanical analysis (3D motion capture with a VICON system and AMTI force plates) of gait and droplanding tasks at baseline (immediately prior to ACLR), 6 months (6M), 1 year (1Y), 2 years (2Y) and 3 years (3Y) after ACLR. To evaluate meniscal matrix biochemical changes, T1r and T2 relaxation times of the meniscus were calculated. Paired t-test was used to examine the differences between ACLR and contralateral knee. Repeated ANOVA with Tukey's post-hoc comparisons were used to examine the effect of time on meniscal relaxation times and biomechanics. Pearson's productmoment correlations (R) were used to assess the associations between biomechanics and MRI relaxation times within the ACLR patients. Results: The ACLR knee exhibited significantly lower peak knee flexion moment (pKFM) and peak knee flexion angle (pKFA) during gait at 6 months (6M) after ACLR compared to BL and continued to decrease until 3Y. Additionally, the ACLR knee exhibited significantly lower peak vertical ground reaction force (pVGRF) parameters and sagittal plane joint biomechanics (pKFM and pKFA) during landing at 6M. However the differences were no longer present at 3Y (Fig.1). Mean T1r/T2 values of meniscus of ACLR knees were significantly higher than contralateral and control knees in the lateral and medial posterior horns up to 1 year (P < 0.05), however, the differences were not seen at 3Y (Fig.1). Peak VGRF, peak KFM and limb symmetry index of peak VGRF at 6M during landing had significant negative correlations with changes of T2 value in medial posterior horn from 6M to 3Y (P ¼ 0.010e0.012) (Fig.2). Conclusions: Although mean T1r and T2 values of meniscus seen prior to ACLR improved after 3 years, approximately 30% of ACLR patients did not show decreases (improvement) from 6 months to 3 years. Patients with lower peak VGRF, KFM and LSI at 6M during landing showed less recovery (as indicated by T2 values) in medial posterior horn from 6M to 3Y, suggesting that abnormal landing biomechanics during the early stage of recovery might be potential biomarkers for predicting medial meniscal abnormality after ACLR.Purpose: The aim of the study is to investigate the influences of the conti...