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Osteochondritis dissecans (OCD) of the knee is a focal, idiopathic, subchondral bone necrosis that may result in detachment of an osteochondral fragment and potentially form a loose body within the joint.

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• It primarily affects the medial femoral condyle and is a key cause of knee pain in adolescents and young adults.

Epidemiology

• Common in adolescents (10–20 years); affects males more than females.
• Incidence: ~15–30 per 100,000.
• Juvenile OCD (open physis): better healing potential.
• Adult OCD (closed physis): more prone to non-healing and loose bodies.

Etiology

Multifactorial:

• Repetitive microtrauma or overuse.
• Ischemia of subchondral bone.
• Genetic predisposition.
• Mechanical factors (e.g., abnormal loading).

Clinical Presentation

• Vague knee pain, worse with activity.
• Swelling or joint effusion.
• Mechanical symptoms: catching, locking (if unstable or loose body).