Longitudinal Multiparametric Quantitative MRI Evaluation of Graft Maturity Following Anterior Cruciate Ligament...

Background/Objectives: Objective, non-invasive biomarkers are needed to track anterior cruciate ligament (ACL) graft maturation and support individualized return-to-sport decisions. This study evaluated a single-session multiparametric quantitative MRI (qMRI) protocol for longitudinal assessment of ACL graft microstructural evolution and its association with patient-reported outcomes. Methods: Twenty-eight patients undergoing primary ACL reconstruction with hamstring autografts underwent multiparametric qMRI (T1, T2*, R2*, and PD mapping) at 1, 3, 6, and 12 months. The contralateral native ACL served as a within-subject control. IKDC, Lysholm, and VAS scores were recorded at each visit. Linear mixed-effects models were used to test longitudinal changes. Correlations of baseline-normalized changes between adjacent visits were used to evaluate imaging-clinical associations. Results: All qMRI parameters changed significantly over time (all p < 0.001). At 1 month, T1, PD, and T2* were lower and R2* higher than the contralateral native ACL (all p < 0.001). Thereafter, T1, PD, and T2* increased and R2* decreased, with most metrics approaching contralateral values by 3-6 months (all p < 0.05), and changes entered a plateau after 6 months (all p > 0.05). IKDC, Lysholm, and VAS improved over time (all p < 0.001), mainly before 6 months. Greater early T2* increases and R2* decreases (1-3 months) were associated with less pain relief and smaller Lysholm improvement (p < 0.05); no significant associations were observed from 6-12 months. Conclusions: Single-session multiparametric qMRI sensitively captures ACL graft maturation and highlights 3-6 months as a critical remodeling window, providing objective biomarkers to complement clinical assessment for individualized rehabilitation monitoring and return-to-sport timing.