In vivo cartilage strain differentiates symptomatic, asymptomatic, and healthy knees six months after ACL...

Alterations in cartilage mechanical properties may signal early degenerative changes preceding clinical or radiographic evidence of osteoarthritis. MRI-based techniques may detect these early pre-osteoarthritic tissue changes, when interventions may be most effective. This study used quantitative relaxometry and displacements under applied loading by MRI (dualMRI) to compare cartilage mechanics and composition between healthy knees and those 6 months post-anterior cruciate ligament reconstruction (ACLR), as a clinically-meaningful model of early joint and tissue injury.

Participants included individuals 6±2 months post-ACLR (n=35; M=13, F=22; age=26±6 yrs; BMI=24±4) and age-, and BMI-matched healthy controls (n=20; M=10, F=10; age=27±5 yrs; BMI=25±6). All underwent T1rho, T2, and T2* mapping, in addition to dualMRI during controlled varus loading. Medial femoral and tibial cartilage were segmented for analysis. In-plane Green-Lagrange and octahedral (von Mises) strains were calculated. Group comparisons were made using linear mixed effects models (α = 0.05).

Compared to healthy controls, ACLR knees showed higher mechanical strain in medial compartments. Among ACLR participants, symptomatic individuals showed greater medial femoral shear (0.021 [0.0016, 0.04]) and octahedral (von Mises) (0.027 [0.009, 0.063]) strain than asymptomatic individuals. Post-ACLR knees showed elevated T1rho (7.05 [0.32, 14.41]) and T2 (5.06, [0.99, 9.13]) in the medial femoral cartilage and reduced T2 (-11.5 [-22.89, -0.07]) and T2* (-4.66 [-7.56, -1.76]) in the medial tibial cartilage. However, relaxometry was less effective in distinguishing symptomatic from asymptomatic knees.

This study highlights the clinical utility of dualMRI to non-invasively quantify cartilage mechanical alterations post-ACLR, potentially identifying individuals at elevated OA risk. Shear strain metrics differentiated symptomatic from asymptomatic individuals, while T2 mapping distinguished ACLR from healthy knees but not symptom severity.