Lesions of cartilage and bone around the knee.

A variety of bone and cartilage abnormalities can be demonstrated on magnetic resonance imaging (MRI), which can play an important role in the diagnosis and management of these abnormalities. Ischemic bone lesions, including medullary bone infarction, primary osteonecrosis, and the osteochondroses, can be precisely evaluated as to their anatomic locations and relationship to overlying cartilage. Osteochondritis dissecans may also be diagnosed and staged. Presence of subchondral fractures and bone contusions, which are frequently associated with ligament and meniscal injuries, can also be diagnosed and followed; these conditions may play a role in the evolution of osteoarthritis. The changes of osteoarthritis, including cartilage abnormalities, cyst formation, and loose bodies, can be evaluated; this evaluation may be important in the assessment of therapies. Stress fractures often have characteristic appearances, and MR may be used in making this diagnosis, especially when symptoms and other imaging are unclear. Diffuse marrow disorders including hemoglobinopathies and neoplasia are also well demonstrated.