Osteochondritis Dissecans of Knee (OCD)

A lesion of the cartilage and bone due to necrosis and loss of continuity of the underlying bone. The OCD lesion can remain in contact with the adjacent bone, maybe partially separated or completely separated. The articular cartilage surface may be intact or may be breached allowing communication of the joint fluid with the bone.

Etiology of this lesion is not known. Theories range from abnormal vascular anatomy (leading to ischemic injury of the bone), abnormal ossification of the epiphysis, trauma, endocrine imbalances or some combination of the above. There is a history of trauma to the knee in 40% of patients. About 50% of the loose bodies in knee are due to OCD lesions.

The most common site is the medial femoral condyle (80%). Other sites are the lateral femoral condyle (15%), and the patella (5%).

Males are 3 times more likely to be affected than females.

Frequently these present insidiously without a traumatic event as a painful knee with vague, poorly localized symptoms. The pain usually is only with the weightbearing and does not develop at rest. Sometimes “locking”, “popping”, or “clicking” will also be present with knee motion and walking. Swelling is variable.

Plain radiographs will identify the vast majority of lesions. OCDs appear as crescent-shaped defects in the bone, sometimes with small flecks of bone within the crater. Sometimes a magnetic resonance imaging scan (MRI) is needed to evaluate suspicious lesions that appear to be OCD lesions.

MRIs are typically used to evaluate documented OCD lesions in order to assist in planning treatment. Bone scans and computed tomography (CT) scans are currently less frequently utilized due to the large amount of information available with MRIs.

In children with open growth plates, there is a higher chance for spontaneous healing with activity modification or immobilization than in adults. If the articular surface is intact, protected activities and possible crutch use for 2-3 months may produce healing. This is especially true in girls younger than the age of 11 and boys younger than 13 years of age. If the articular surface is disrupted or there is a loose fragment, immobilization is unlikely to succeed, and surgical treatment is usually advocated.

The primary prognostic factors are patient age and skeletal maturity. The less mature the patient, the better the prognosis, with best results seen in the juvenile form (before adolescence), where full recovery is the usual outcome. In the adolescent type (partial skeletal maturity), outcome is unpredictable. With the adult type (skeletally mature), a guarded prognosis is the rule.

The optimal treatment is controversial. The basic concepts are:1) fragmented displaced lesions are best excised 2) painful lesions in continuity with surrounding bone should be drilled, 3) displaced small lesions should be excised and curetted, and 4) displaced large lesions with bone attached to cartilage should be fixed with or without bone grafting. A wide variety of fixation devices, bone grafting techniques, and surgical approaches exist.