In vivo high-resolution MRI (7T) of femoro-tibial cartilage changes in the rat anterior cruciate ligament transection model of osteoarthritis: a cross-sectional study.

Objective: To assess OA-related changes in mean compartmental femorotibial cartilage thickness in rat knees by three-dimensional (3D) MRI (7T).

Methods: MRI was performed in vivo at 7T on OA and untouched contralateral knee joints. Gradient Echo Fast Imaging 3D MR images were acquired sequentially in surgically induced OA (D0) in 40 Wistar rats (anterior cruciate ligament transection). Mean femoral (trochlear, lateral and medial) and tibial (lateral and medial) cartilage thicknesses were quantified from a 2D MRI slide in weight-bearing areas and from a 3D MRI data set. At each time-point [Day (D)8, D14, D21, D40 and D60], eight animals (16 knees) were sacrificed for concomitant histomorphometry.

Results: As body weight dramatically increased throughout the experiment (+150%, baseline vs endpoint), all compartmental mean cartilage thicknesses noticeably decreased (D8, D14) and then remained relatively stable. Femoral compartments in OA knees were thinner at the end of the experiment than in contralateral age-matched knees. Conversely, lateral and medial tibial cartilages were thicker than controls. Histological correlation was significant only in untouched healthy cartilages (3D better than 2D).

Conclusions: 3D MRI (7T) enables in vivo monitoring of compartmental changes in OA-related femorotibial rat cartilage thickness vs contralateral age-matched knees.