Quantitative UTE MRI Differences in the Meniscus Following ACL Reconstruction: A Prospective Cohort Study Using 3D Ultrashort Echo Time Adiabatic T1rho and Magnetization Transfer Imaging

Background ACLR is associated with altered joint loading and increased risk of post‐traumatic osteoarthritis. Conventional MRI has limited sensitivity to early meniscal differences because of short‐T2 signal decay and magic‐angle effects. Purpose To evaluate whether 3D ultrashort echo time imaging‐based adiabatic T1rho (UTE‐Adiab‐T1rho) and ultrashort echo time imaging‐based macromolecular fraction (UTE‐MMF) identify regional quantitative MRI differences after ACLR. Study Type Prospective longitudinal cohort study. Population 30 control scans, 19 ACLR scans at 6–12 months, and 13 ACLR scans at 12+ months were analyzed. Mean ages were 34.5, 34.5, and 37.2 years; female/male counts were 15/15, 9/10, and 8/5. Field Strength/Sequence Participants underwent 3‐T knee MRI with 3D fat‐saturated UTE‐Adiab‐T1rho and UTE magnetization transfer sequences. Assessment UTE‐Adiab‐T1rho and UTE‐MMF maps were generated with single‐component exponential and two‐pool magnetization transfer models. Values were extracted from four meniscal regions of interest by a blinded reader, with blinded redelineation in a subset. Patient‐reported outcomes included International Knee Documentation Committee, Knee Injury and Osteoarthritis Outcome Score, and Western Ontario and McMaster Universities Osteoarthritis Index scores. Statistical Tests Linear mixed‐effects models accounted for repeated observations. Benjamini‐Hochberg FDR correction was applied. Results UTE‐Adiab‐T1rho showed significant group ( q = 0.001) and region ( q < 0.001) effects. Compared with controls, UTE‐Adiab‐T1rho was higher in LAM at 6–12 months (+5.60 ms; q = 0.035) and 12+ months (+7.09 ms; q = 0.028), and in LPM at 12+ months (+6.35 ms; q = 0.035). UTE‐MMF showed significant group ( q = 0.041) and region ( q < 0.001) effects. LPM UTE‐MMF was lower than controls at 6–12 months (−3.56 percentage points; q = 0.028) and 12+ months (−3.10 percentage points; q = 0.049). No 6–12 versus 12+ month MRI or PROM contrast survived FDR correction. MRI‐PROM associations were not FDR‐significant (all q ≥ 0.383). Data Conclusion UTE‐Adiab‐T1rho and UTE‐MMF mapping identified regional MRI differences after ACLR. Pairwise differences were concentrated in lateral regions, but corrected group‐by‐region interactions were not significant. PROMs were worse after ACLR but did not differ between postoperative windows after correction. Evidence Level 2. Technical Efficacy Stage 2.