Magnetic resonance imaging osteonecrosis pattern within an osteochondral dowel allograft.

A 22-year-old male with a history of a previously debrided large posttraumatic osteochondral lesion of the lateral femoral condyle presented to our institution for further treatment due to persistent pain and instability. He was treated with a large cryopreserved osteochondral dowel allograft and remained clinically asymptomatic with no pain, locking, or instability at his 12-month, 18-month, and 42-month follow-up appointments. However, his 12-month magnetic resonance imaging (MRI) examination demonstrated an osteonecrosis pattern within the osseous component of the allograft. Six months later, the osteonecrosis pattern decreased in size, and 30 months later had completely resolved. The allograft was otherwise stable in appearance. The MRI appearance was most likely due to a normal maturation process of bone healing within osteochondral allograft dowel, referred to as "creeping substitution".