Osteochondritis Dissecans

A joint disorder characterised by separation of a segment of subchondral bone, together with its overlying articular cartilage, from the surrounding normal bone.

It most commonly affects the knee (particularly the lateral aspect of the medial femoral condyle), though it also occurs at the elbow, ankle, and other joints. It predominantly affects active adolescents and young adults.

The cause is believed to be a combination of repetitive microtrauma and localised vascular insufficiency at the affected subchondral bone site.

Management is determined by the child's skeletal maturity and the stability of the osteochondral fragment. Skeletally immature individuals with open growth plates have a more favourable natural history and healing potential than skeletally mature individuals.

Pathophysiology

• Repetitive mechanical stress at a characteristic site is believed to produce localised subchondral bone injury and vascular compromise. The most common site is the lateral aspect of the medial femoral condyle at the knee, reflecting the pattern of contact and loading there, particularly with repetitive impact or rotational loading.
• The osteochondral segment then separates progressively from the surrounding normal bone.
• The fragment may remain stable, with an intact cartilage surface and no significant displacement. Alternatively it may become unstable, with progressive separation and, in the most severe cases, complete detachment to form a loose body within the joint.
• Stability status is directly relevant to both symptoms and treatment.
• Skeletally immature individuals, with open growth plates and a greater capacity for spontaneous healing, have a more favourable natural history.
• In skeletally mature individuals, spontaneous healing is considerably less likely and surgical intervention is more frequently required.

• Vague, poorly localised joint pain, typically exacerbated by activity and relieved by rest, with intermittent swelling, is the characteristic presenting pattern.
• Onset is often insidious in early disease. Symptoms are frequently present for a considerable period before diagnosis because the presentation is non-specific and gradual.
• Mechanical symptoms (catching, locking, or a sensation of instability) develop where the fragment becomes unstable or detached and forms a loose body within the joint.
• This is a more advanced pattern of presentation. It points to a likely need for surgical rather than conservative management.
• On examination, joint line tenderness at the characteristic site of involvement may be present, with a palpable effusion in some cases.
• The Wilson test is a further examination technique for the classic medial femoral condyle location. It involves internal rotation of the tibia during knee extension; reproduction of pain suggests impingement of the tibial spine against the osteochondral lesion. It is imperfectly sensitive and specific.
• A history of sports involving repetitive impact, jumping, or rotational loading supports clinical suspicion. So do the characteristic age range (adolescents and young adults) and activity-related pain.

• Plain radiography is an appropriate initial investigation. Views optimised for the classic medial femoral condyle location (including a tunnel or notch view) are used.
• Radiography has limited sensitivity for early or subtle disease. It also has limited capacity to assess fragment stability, which is critical.
• Magnetic resonance imaging is the investigation of choice. It is more sensitive for detecting the lesion and gives detailed information on fragment stability.
• High-signal fluid tracking beneath the fragment indicates instability. In the most severe cases there is complete fragment detachment with a visible loose body.
• The stability assessment directly informs treatment decisions.
• Assessment of skeletal maturity is an essential additional component of evaluation. It combines clinical assessment of pubertal status with, where relevant, radiographic assessment of growth plate status.
• Skeletal maturity bears directly on the expected natural history and the treatment approach.

• Skeletally immature individuals with a stable lesion are generally managed conservatively, given their substantial capacity for spontaneous healing.
• Treatment comprises activity modification, avoiding high-impact activities that provoke symptoms or stress the affected joint. Some protocols add a period of protected weight-bearing.
• Regular, structured clinical and imaging reassessment monitors healing progression.
• Skeletally mature individuals with a stable lesion generally require surgical treatment. So do skeletally immature individuals with a stable lesion not responding to an adequate trial of conservative management.
• Surgery typically comprises arthroscopic drilling of the affected subchondral bone. The aim is to stimulate a localised healing response by creating new vascular access channels to the region.
• Unstable lesions, or those with an associated loose body, generally require surgical treatment.
• Fixation of the fragment is used where its size, location, and quality are suitable, aiming to preserve the individual's own native articular cartilage.
• Where fixation is not feasible or the fragment is not viable, the fragment is removed and a cartilage restoration procedure is performed. Options include microfracture, osteochondral autograft or allograft transplantation, or autologous chondrocyte implantation, chosen according to defect size and location and surgeon and institutional expertise and preference.
• Structured rehabilitation follows any surgical intervention. Return to activity and sport is staged and gradual, according to the procedure performed and objective evidence of adequate healing.
• Regular, ongoing follow up incorporates clinical assessment and, where indicated, serial imaging. This monitors healing and identifies progression or secondary joint complications.
• Patient and family education covers the expected natural history and the importance of adherence to any recommended activity modification. Management is individualised across presentation patterns and skeletal maturity.