Identification of the subchondral bone plate breach found in subchondral bone cysts (SBC) in the OA rat knee. Sagittal micro-CT (a) and high-field MRI (b) sections were used to observe and monitor SBC in vivo. End stage histological analysis confirmed separation in the subchondral bone plate (c - arrow, 10 × magnification of Safranin-O with fast-green counter stain). Note, the fibrocartilage repair tissue adjacent the SBC (horizontal arrowheads) and breach to the subchondral plate. Remaining bone tissue between the repair tissue and the SBC lacks the presence of osteocytes (vertical arrowhead) that indicates focal necrosis. Note the 'pear' shape of the intra-osseous lesion, consistent with SBC in humans. micro-CT, micro computed tomography; MRI, magnetic resonance imaging; OA, osteoarthritis.