Osteochondritis Dissecans

Definition

• A condition whereby a segment of cartilage with subchondral bone separates from the articular surface

Incidence

• most common in the knee
• usually unilateral
• imost common cause of a loose body in the knee joint of a young person
• 15-20 knees / 100,000
• more common in males
• in the 2nd decade

Aetiology

• 2 schools of thought
  • 1. due to an area of bone infaction with subsequent separation of a fragment
  • 2. due to an osteochondral fracture which fails to heal
    • this has been supported by
      • occurrence of OCD especially in athletic young people
      • associated with trauma to the joint e.g. direct blow, patellar dislocation
      • production of OCD lesions in cadavic knees by applying axial compression & rotatory forces
      • cadaveric studies showing that direct blow to the flexed knee can produce the classic OCD lesion at the lateral MFC

Associations

• significant valgus or varus deformity – 14%
• ACL deficiency – 7%
• patellar subluxation/ dislocation – 16%

History

• pain often activity related, usually of low intensity

Examination

• wasting,
• tenderness over the lesion,
• joint effusion

Wilsons Sign

• flex knee to 90°
• internally rotate tibia
• slowly extend the knee- in patients with OCD
• pain is produced at ~ 30° of flexion & is relieved with lateral rotation

Investigations

X-rays

• AP/ Lateral/Tunnel
  • lesions most common on lateral aspect of MFC & posterior part of LFC
  • rare on the patella & the trochlea

CT

• Defines lesion size, location and bony fragment integrity
• Useful when MRI is unavailable or contraindicated
• CT arthrography showing contrast beneath the fragment suggests instability
• Poor assessment of articular cartilage and the subchondral interface
• Radiation dose limits use in children

MRI

• Investigation of choice for lesion size, cartilage integrity and stability
• High T2 signal line beneath the fragment suggests instability
• Subchondral cysts, articular cartilage breach and fluid filled defect also suggest instability
• Instability signs are more reliable in adults than in juvenile lesions
• Detects loose bodies and craters from detached fragments
• Used to monitor healing during non-operative treatment

Arthroscopy

• Definitive assessment of cartilage integrity and fragment stability
• Probing detects softening, fissuring or a mobile fragment
• Guhl arthroscopic staging grades lesions from intact to detached with loose body
• Allows treatment at the same sitting with drilling, fixation or loose body removal

Natural History

• Children
  • readily heals especially if on the posterior surface of the condyles
• Not all lesions spontaneously heal
  • unstable
  • lesions in the classical lateral MFC position
    • less than 50% heal spontaneously

Treatment

• Depends on
  • age of patient,
  • stage of disease
  • size & location of the lesion

Non-operative

• Indication
  • if lesion is intact & nontender
    • observation
    • rest
    • analgesia
  • if tender
    • splintage with R.O.M. exercises

Operative

• indication
  • if symptomatic despite nonoperative treatment
  • displacement at any age
  • persistence after physeal closure
• options
  • if cartilage intact
    • simple drilling of fragment with 1mm K- wire
  • loose or sequestered lesions
    • should be replaced & fixed
    • if lesion small e.g. < 5mm can excise

Prognosis

• incidence of Osteoarthritis higher
  • in patients diagnosed & treated after skeletal maturity
  • large fragment excised

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.