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Osteochondritis dissecans

Definition

A non-inflammatory condition whereby a segment of cartilage with subchondral bone separates from the articular surface

Incidence

  • Most common in the knee
  • Usually unilateral
  • The most common cause of a loose body in the knee of a young person
  • 15-20 knees / 100,000
  • More common in males and in the 2nd decade
  • Bilateral in 20-30%
  • Location
    • Posterolateral MFC (anterior to PCL foot print): 70%
    • LFC : 20%
    • Patella : 10%

Aetiology

Historically there are 2 schools of thought

  1. An area of bone infarction with subsequent separation of a fragment 
  2. An osteochondral fracture, which fails to heal. This has been supported by
    • High incidence of OCD in athletic young people
    • Association with trauma, e.g. direct blow, patellar dislocation
    • Association with other knee internal derangement
      • Significant valgus or varus deformity : 14%
      • ACL deficiency : 7%
      • Patellar subluxation / dislocation : 16%
    • Production of OCD lesions in cadaveric knees by applying axial compression and rotatory forces
    • Cadaveric studies showing that direct blow to the flexed knee can produce the classic OCD lesion at the lateral MFC

Clinically

  • Pain is often activity related, usually of low intensity
  • Wasting
  • Tenderness over the lesion
  • Joint effusion
  • If fragment is detached and floating, locking and sharp pain may occur
  • Wilsons sign : flex knee to 90o, internal rotate tibia, slowly extend the knee. In patients with OCD, pain is produced at 30o of flexion and is relieved with lateral rotation

Natural History

  • Lesion heals in children readily, especially if located on the posterior surface of the condyles
  • Adult cases have take to routes :
    • 25% of lesions detach and lead to early OA
    • 75% will have spontaneous healing
    • Healing takes 3-4 mo
  • Not all lesions heal spontaneously
    • Unstable (detached) lesions in the classical lateral MFC position have guarded prognosis
    • Less than 50% heal spontaneously

Investigation

  • AP / Lat / Tunnel X-Rays
  • CT
  • MRI
  • Bone scan can be used to differentiate acute from chronic lesions
  • Arthroscopy

GUHL Arthroscopic classification

Stage

Pathology

Cartilage

A

Subchondral fracture

soft and yellowish

B

Incomplete separation

cracked cartilage

C

Complete undetached

Cartilage lesion all over

D

Complete detached

Crater

Treatment

  • Depends on age of patient, stage of disease, size and location of the lesion
  • Conservative treatment, i.e. observation, rest, analgesia; only if lesion is intact and non tender
  • If tenderness persists, splint with ROM exercises
  • Operative treatment
    • If symptomatic despite conservative treatment
    • Displacement at any age
    • Persistence after physeal closure
    • Options
      • If cartilage intact, simple drilling of fragment with 1 mm K wire
      • loose or sequestered lesions should be replaced and fixed
      • If lesion small, e.g. < 5 mm, can be excised

Prognosis

  • Incidence of OA is higher in patients diagnosed and treated after skeletal maturity and those with large fragment excised
  • Favorable prognosis if
    • Young at presentation
    • Open physis
  • Unfavorable prognosis if
    • Lesions of lateral femoral condyle and patella
    • Detached segment
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