Bone marrow lesions (BMLs) are well-reported to cause pain and result in morbidity across species; and appear to be early indicators of inflammation accelerating degenerative changes within the joint. The investigators have previously developed a reproducible experimental model for BMLs using the ovine stifle (knee) joint, but have not evaluated the long-term effects (>3 months). The objective of this study was to investigate changes within the femorotibial joint through volumetric imaging over time with experimentally-induced BMLs. Four skeletally-mature crossbred ewes were used for this prospective study. BMLs were bilaterally induced using a 1.1 mm Steinmann pin, penetrating from the articular cartilage and into trabecular bone. Magnetic resonance imaging (MRI, 3 T) and computed tomography (CT) were performed pre-operatively, and at 2 weeks, 3, 6, 9, 12, 15, and 18 months post-operatively. Semi-objective gait analysis was performed weekly for the first month and then prior to each imaging timepoint. BMLs were reliably visible in the medial femoral condyle on high-field MRI at 2 weeks post-operatively. The overall area (P < 0.05) and volume of fluid signal (P < 0.05) of BMLs decreased on fluid-sensitive MR sequences over time. Subchondral cyst-like lesions were visible by 6 months on MRI. An increase (P < 0.05) in CT attenuation was observed in the region of BML compared to baseline. This study demonstrates BMLs are dynamic and alter the subchondral bone over time, including the formation of cyst-like lesions. Serial MR and CT imaging suggest the composition of BMLs change as the BML ages.
