Osteochondritis dissecans

What is osteochondritis dissecans?

Osteochondritis dissecans (OCD) is a pathological process affecting the subchondral bone (most often in the knee joint) of children and adolescents with open growth plates (juvenile OCD) and young adults with closed growth plates (adult OCD). Osteochondritis dissecans may lead to secondary effects on joint cartilage, such as pain, oedema, possible formation of free bodies and mechanical symptoms, including joint locking. OCD may lead to degenerative changes if left untreated.¹

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. 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. The cause of osteochondritis dissecans is unknown.²

There are two main types of osteochondritis dissecans:

• Adult form (after the physis has closed).

• Juvenile form (occurring with an open epiphyseal plate).

Epidemiology

Prevalence

OCD most often affects the knee.² The exact prevalence of OCD is unknown but prevalence figures of between 15 and 29 per 100,000 have been reported. OCD is more common in males.³

Distribution^{4 5}

• Osteochondritis dissecans most commonly affects the knee joint (75% of 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.

• Osteochondritis dissecans can affect more than one site and may be bilateral in 20-30% of cases.

Risk factors

• Trauma (about half of cases).

• Male sex (although incidence is 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.

Presentation⁶

Osteochondritis dissecans symptoms

• Osteochondritis dissecans usually presents in teenage years or the early 20s.

• It can affect younger children who are very active in sports.

• It 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.

• The 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 of osteochondritis dissecans, 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 the knee fully flexed, it should be possible to palpate the area directly on the articular cartilage of the medial femoral condyle, which is usually tender.

• Wilson's sign has been used for demonstrating the presence of a medial femoral condyle lesion, although its diagnostic merit has been challenged by some:⁷
  

  • 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.

Early diagnosis 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; they thus have the potential to heal with conservative management if detected early.⁸

Differential diagnosis^{9 10}

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 - eg, Osgood-Schlatter disease - may cause similar symptoms but the pain is usually localised to the relevant tendinous insertion with overlying tenderness and swelling.

Investigations¹

• X-ray shows a subchondral crescent sign or loose bodies. For the knee, request anteroposterior, lateral and tunnel (with knee in flexion) views.

• Ultrasound may be useful and cost-effective, and provide dynamic scanning with motion of the affected joint.

• CT demonstrates the size and site of the lesion.

• MRI is currently the most important examination, because it enables analysis on bone quality, oedema, possible subchondral separation and cartilage condition.

• Scintigraphy using technetium 99 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. However, this technique has been questioned because of the time taken for obtaining the images and the risk from administration of contrast.

Staging⁴

Osteochondritis treatment and management¹

There is a lack of reliable randomised controlled clinical trials. In general, the approaches used take into consideration the maturity of the growth plate, situation of the subchondral bone, stability of the lesion, dimensions of the fragment and integrity of the cartilage. Conservative treatment is more frequently successful if performed before growth plate closure.¹¹ Stable lesions have a better prognosis.

Conservative treatments for osteochondritis dissecans include analgesic and anti-inflammatory medication, load reduction (crutches), use of an immobiliser, gentle physiotherapy and even the use of plaster casts. The use of plaster casts has been criticised because of the risk that this could predispose towards chondral degeneration and joint stiffness. Total restriction of physical activities may lead to resolution of the process among younger patients.

Surgery is indicated in cases in which conservative treatment fails, for loose bodies and in cases of unstable or dislocated lesions, especially for adult OCD. Surgical approaches include:^{12 13}

• 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 transplantation.¹⁴

Complications¹⁵

OCD can result in pain, functional impairment, knee joint effusions, loose body formation and osteoarthritis.

Osteochondritis dissecans prognosis

• Osteochondritis dissecans prognosis depends on the age of the patient, the affected joint and the stage of the lesion at presentation.

• Younger patients with small, stable medial femoral condylar lesions have the best prognosis.^{16 17}

• Unstable lesions can heal after stabilisation; however, long-term prognosis is not clear. Chronic loose fragments can be difficult to fix and tend to heal poorly.

• Excision of large lesions from weight-bearing zones also tend to give poor results.⁸