Introduction

Osteochondritis dissecans (OCD) is a pathological process affecting the subchondral bone (most often in the knee joint) with secondary effects on the joint cartilage, including pain, oedema, free bodies and mechanical dysfunctions. It affects children and adolescents with open growth plates (juvenile OCD) and young adults with closed growth plates (adult OCD). OCD may progress to degenerative changes if untreated.

Epidemiology

  • Incidence: 1.00 cases per 100,000 person-years
  • Peak incidence: 6-15 years
  • Sex ratio: more common in males 3:1
Condition Relative
incidence
Osgood-Schlatter disease200.00
Osteochondritis dissecans1
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+

Aetiology

Risk factors
  • Trauma
  • Male
  • Genetic

Clinical features

Patients typically present with a subacute onset of:
  • Knee pain and swelling, typically after exercise
  • Knee catching, locking and/or giving way - more constant and severe symptoms are associated with the presence of loose bodies
  • Feeling a painful 'clunk' when flexing or extending the knee - indicating the involvement of the lateral femoral condyle

Signs:
  • Joint effusion
  • Full range of movement in the joint without signs of ligamentous instability
  • External tibial rotation when walking - if medial femoral involvement
  • Tenderness on palpation of the articular cartilage of the medial femoral condyle, when the knee is flexed
  • Wilson's sign for detecting medial condyle lesion - with the knee at 90° flexion and tibia internally rotated, the gradual extension of the joint leads to pain at about 30°, external rotation of the tibia at this point relieves the pain

Investigations

Early diagnosis is important. Clinical signs may be subtle in the early stages hence there should be a low threshold for imaging and/or orthopaedic opinion.

Investigations:
  • X-ray (anteroposterior, lateral and tunnel views) - may show the subchondral crescent sign or loose bodies
  • MRI - used to evaluate cartilage, visualise loose bodies, stage and assess the stability of the lesion
  • CT - may be used in preoperative planning and in cases where MRI is not available or contraindicated
  • Scintigraphy - may be used to guide treatment as it may show increased uptake in the fragments - a sign of osteoblastic activity