The separation of articular cartilage and subchondral bone fragment from a joint surface was misnamed as osteochondritis dissecans in the nineteenth century in the false belief that there was an underlying inflammatory pathology.¹ We know now that this is not the case but the name has stuck. The separated fragment may become avascular and exist as a loose body within the joint. It is the most common cause of a loose body in the joint space of adolescent patients.

There are two main types of osteochondritis dissecans:

1. Adult form (after the physis has closed)
2. Juvenile form (occurring with an open epiphyseal plate)

Some believe that the adult form represents undiagnosed, persistent disease from childhood. The aetiology is uncertain but thought to be due to a multifactorial combination of:

• Genetic predisposition
• Ischaemia
• Repetitive trauma
• Abnormal ossification
• Ligamentous laxity
• Biomechanical factors

Epidemiology

Prevalence

This is a rare disorder - affecting the knee, there are 3-6 cases per 10,000 adult population.²

Distribution³

• It most commonly affects the knee joint (75% cases). About 85% of knee lesions are on the medial femoral condyle.
• The elbow and ankle are the next most common joints affected. In the elbow, it affects the capitellum of the humerus and, in the ankle, it affects the talar dome.
• Very rarely it affects articulations of the shoulder, hand, wrist or hip.
• The disease can affect more than one site and may be bilateral in 20-30% cases.

Risk factors

• Trauma (about half of cases)
• Male sex (although incidence increasing in women and girls)
• Overuse due to sporting activity
• Familial pattern in about 10% of cases
• Ligamentous weakness
• Genu valgum/varum
• Meniscal lesions in the knee

Presentation

Symptoms

• Usually presents in teenage years or early 20s.
• Can affect younger children who are very active in sports.
• May only become symptomatic in later life.
• Around 5% of middle-aged patients with osteoarthritis of the knee are thought to have suffered osteochondritis dissecans in earlier life.
• Usual feature is vague, aching joint pain and swelling worsened by activity.
• Locking, catching and giving-way may be present, particularly with intra-articular loose bodies.
• When the lateral femoral condyle is affected, patients commonly feel a painful 'clunk' when flexing or extending the knee.

Signs

• In most cases, there is a full range of movement in the joint without signs of ligamentous instability. Joint effusion is often present, particularly if there has been trauma.
• With medial femoral involvement, external tibial rotation when walking is typical.
• With knee fully flexed should be able to palpate the area directly on the articular cartilage of medial femoral condyle, which is usually tender.
• Wilson's sign⁴ has been used for demonstrating the presence of a medial femoral condyle lesion although its diagnostic merit has been challenged by some.⁵ With the knee flexed to 90° and the tibia internally rotated, gradual extension of the joint leads to pain at about 30°. External rotation of the tibia at this point relieves the pain.

Always consider the diagnosis, as early pick-up is vital. Clinical findings can be subtle so have a low threshold for ordering X-rays or requesting an orthopaedic opinion. Juvenile lesions are typically stable, with an intact articular surface, and thus have the potential to heal with conservative management if detected early.⁶

Differential diagnosis

Alternative causes of the symptoms should be sought where there is no radiological confirmation of osteochondritis dissecans. Consider:

• Inflammatory arthritides
• Osteoarthritis
• Bone cysts
• Septic arthritis

In children and adolescents, traction apophysitis, e.g. Osgood-Schlatter's disease, may cause similar symptoms but the pain is usually localised to the relevant tendinous insertion with overlying tenderness and swelling.

Investigations

• X-ray shows subchondral crescent sign or loose bodies. For the knee, request anteroposterior, lateral and tunnel (with knee in flexion) views.
• CT demonstrates size and site of lesion.
• MRI is best for evaluation of overlying cartilage and is used to stage and assess stability of the lesion, which will determine subsequent management. It is also useful for prognosis.
• Scintigraphy may show increased uptake in the fragments. Osteoblastic activity is used to guide treatment since it relates to a greater chance of healing with conservative treatment.

Staging

Management

Non-drug

Conservative measures should be used to treat stable (Grade I and II) lesions and younger patients with open epiphyses. Many cases will resolve with this regimen including:

• Stop sport/precipitating activities for 6-8 weeks.
• Gentle physiotherapy.
• Immobilisation, protected weight bearing and bracing are advocated by some.
• Reassessment at 3 months and, if asymptomatic, allow patient to monitor condition themself.

Drugs

Simple analgesics or NSAIDs may be used to treat pain. NSAIDs will not affect the disease course as there is no significant inflammatory component.

Surgical

Surgery is usually undertaken when:

• Conservative management has failed.
• The lesion is unstable (Grade III).
• Loose bodies are present (Grade IV).

Surgical approaches include¹:

• Arthroscopic subchondral drilling to promote revascularisation
• Arthroscopic debridement and fragment stabilisation
• Arthroscopic excision, curettage, and drilling
• Open removal of loose bodies, reconstruction of the crater base and potential replacement with fixation
• Bone grafting and autologous chondrocyte transplantation⁷

Complications

• Chronic pain
• Functional impairment
• Osteoarthritis

Prognosis

Prognosis depends on the age of the patient, the affected joint and stage of lesion at presentation. Younger patients with small, stable medial femoral condyles have the best prognosis.⁸ Unstable lesions can heal after stabilisation, but long-term prognosis is not clear. Chronic loose fragments can be difficult to fix and tend to heal poorly. Excision of large lesions from weightbearing zones also tend to give poor results.⁶