Osteochondritis Dissecans

• Sub-articular, post-traumatic necrosis

• Occurs only on convex surfaces of bone

• Medial condyle of femur

• Capitellum

• Proximal surface of talus

• Head of 1^st metatarsal

• Most patients are athletic

• Direct blow is more common cause than a rotational injury

• Knee lesions are more common amongst high jumpers

• Most common cause of an intra-articular loose body

• In adults, loose body contains larger fragment of cartilage than bone

• Possible outcomes

• Death of bony, but not cartilaginous, portion of loose body

• Loose body is invisible except to MRI

• Complete resorption of loose body

• Reincorporation or regrowth

• Usually not in adults

• In children, fragment is less likely to separate from bone and therefore more likely to reincorporate

• Cause of a “locking knee”

Osteochondritis dissecans. Blue arrow points to crescentric lucency in the convex
surface of the medial condyle of the knee.

For the same photo without the arrows, click here.

Osteochondritis dissecans. Red arrows point to osteochondral defect and bone edema on T1 and stir
MRI images of the knee in same patient as above.

Osteochondritis dissecans of medial femoral condyle-ovoid fragment
of bone is separated from surface of condyle but does not yet lie freely within the joint.