Longitudinal Multiparametric Quantitative MRI Evaluation of Graft Maturity Following Anterior Cruciate Ligament Reconstruction: A One-Year Prospective Observational Study

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 0.05). 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.