Osteochondritis Dissecans of the Knee

Osteochondritis dissecans (OCD) of the knee is a focal disorder of subchondral bone that can lead to separation of the overlying articular cartilage.

It is juvenile (open physes, better prognosis) or adult (closed physes, worse natural history). It mostly affects active adolescents, with a male predominance.

Stable juvenile lesions can heal with activity modification. Missed unstable or displaced lesions progress to loose bodies and early osteoarthritis.

OCD starts in the subchondral bone, with the articular cartilage initially intact above it. The cause is multifactorial: repetitive microtrauma and early sports specialisation, subchondral ischaemia, tibial spine contact against the medial femoral condyle, genetic factors with familial clustering, and an association between discoid lateral meniscus and lateral femoral condyle lesions.

Sites:

• •Medial femoral condyle, classically its lateral aspect (mnemonic LAME): the commonest site, 64% of lesions in one large paediatric cohort
• •Lateral femoral condyle: most of the rest
• •Patella and trochlea: uncommon

Lesion stability guides management. The ICRS classification is arthroscopic: I stable with intact cartilage; II partial discontinuity, stable on probing; III complete discontinuity, not displaced; IV displaced fragment or loose body.