Multiparametric MR imaging reveals early cartilage degeneration at 2 and 8 weeks after ACL transection in a rabbit model

In this study, the rabbit model with anterior cruciate ligament transection (ACLT) was used to investigate early degenerative changes in cartilage using multiparametric quantitative magnetic resonance imaging (qMRI). ACLT was surgically induced in the knees of skeletally mature New Zealand White rabbits (n = 14). ACL transected and contralateral knee compartments—medial femur, lateral femur, medial tibia, and lateral tibia—were harvested 2 (n = 8) and 8 weeks (n = 6) postsurgery. Twelve age‐matched nonoperated rabbits served as control. qMRI was conducted at 9.4 T and included relaxation times T₁, T₂, continuous‐wave T1p (CWT1p), adiabatic T1p (AdT1p), adiabatic T2p (AdT2p), and relaxation along a fictitious field (TRAFF). For reference, quantitative histology and biomechanical measurements were carried out. Posttraumatic changes were primarily noted in the superficial half of the cartilage. Prolonged T₁, T₂, CWT1p, and AdT1p were observed in the lateral femur 2 and 8 weeks post‐ACLT, compared with the corresponding control and contralateral groups (P < .05). Collagen orientation was significantly altered in the lateral femur at 2 weeks post‐ACLT compared with the corresponding control group. In the medial femur, all the studied relaxation time parameters, except TRAFF, were increased 8 weeks post‐ACLT, as compared with the corresponding contralateral and control groups (P < .05). Similarly, significant proteoglycan loss was observed in the medial femur at 8 weeks following surgery (P < .05). Multiparametric MRI demonstrated early degenerative changes primarily in the superficial cartilage with T₁, T₂, CWT1p, and AdT1p sensitive to cartilage changes at 2 weeks after surgery.