Osteochondritis Dissecans of the Knee

Osteochondritis dissecans (OCD) is an acquired idiopathic lesion of subchondral bone that can affect the overlying articular cartilage. It ranges from softening of the cartilage to complete detachment of a bony fragment (loose body). The knee is the most common location (75% of all OCD).

Etiology

Cause uncertain (multifactorial):

• Repetitive microtrauma: Most accepted theory (active adolescents)
• Vascular insufficiency: Ischemia of subchondral bone
• Genetic factors: Familial clustering reported
• Ossification: Aberrant ossification centre

Epidemiology

• Incidence: 15-30 per 100,000
• Age: Juvenile (open physis) vs Adult (closed physis)
• Gender: Male greater than Female (2:1)
• Bilateral: 20-30% of cases (always xray other knee)

Anatomy

Classic Location:

• Medial Femoral Condyle (MFC): 75% of cases
• Specific Site: Lateral aspect of the MFC (lateral wall of intercondylar notch)
• Other Sites: Lateral femoral condyle (20%), Patella (5%), Trochlea (less than 1%)

Why Lateral MFC?

• Impingement of the Tibial Spine or PCL against the lateral aspect of the MFC during knee motion
• Occurs near the insertion of the PCL

Pathophysiology

1. Subchondral Bone Event: Ischemia or stress fracture of subchondral bone
2. Overlying Cartilage: Initially intact (stable)
3. Separation: Bone fragment separates from parent bone
4. Instability: Cartilage breach allows fluid ingress (unstable)
5. Loose Body: Fragment detaches completely

History

• Pain: Vague, poorly localized knee pain
• Activity-related: Worse with impact/sports
• Swelling: Intermittent effusion, especially after activity
• Mechanical symptoms: Catching, locking (suggests unstable flap or loose body)
• Onset: Insidious, durable

Physical Examination

Inspection:

• Quadriceps atrophy (if chronic)
• Effusion (mild to moderate)
• Gait: Antalgic, tibial external rotation (to avoid impingement)

Palpation:

• Wilson's Sign: Specific but low sensitivity
• Tenderness: Over the classical site (medial femoral condyle) with knee flexed 90°

Rehabilitation Protocol

• Weight Bearing:

  • Drilling: Immediate WBAT (stable)
  • Fixation: Touch-down for 6 weeks (protect repair)
  • Grafting: Non-weight bearing 6 weeks

• Range of Motion:

  • Early passive ROM (prevents stiffness)
  • CPM often used for cartilage repair

• Return to Sport:

  • Conservative: 3-6 months (MRI healing)
  • Surgical: 6-9 months (bone union on CT/MRI)
  • Criteria: No pain, full ROM, radiographic healing

Prognostic Factors

• Age: Strongest predictor. Open physis = Good. Closed = Poor.
• Size: Smaller lesions (less than 2cm) heal better.
• Location: Classic MFC heals better than Patella/Trochlea.
• Stability: Stable heals better than unstable.

Success Rates

• Juvenile Conservative: 50-70% healing rate.
• Drilling: 80-90% success in failed conservative juvenile.
• Fixation: 80-90% success if bone quality good.
• Excision: Poor long-term results (OA risk), good short-term pain relief.

Global Epidemiology

• Incidence roughly 15-30 per 100,000 children and adolescents; rising with year-round single-sport participation worldwide.
• Peak age 10-15 years (juvenile, open physis); a smaller adult cohort presents with closed physes.
• Male predominance approximately 2:1; bilateral in 20-30% (image the contralateral knee).
• Classic site is the lateral aspect of the medial femoral condyle; lateral femoral condyle lesions associate with discoid meniscus.

Side-by-Side Guidance

Registry and Restoration Data

• OCD is a leading indication for cartilage restoration registries (e.g. German KnorpelRegister DGOU, and ICRS-aligned datasets) tracking microfracture, OAT/mosaicplasty, ACI/MACI and osteochondral allograft outcomes.
• Registry signals mirror the literature: fragment preservation and osteochondral restoration outperform excision for long-term joint survival.

High- vs Limited-Resource Practice