OSTEOCHONDRITIS DISSECANS - KNEE
OCD | Juvenile vs Adult | Stable vs Unstable | MFC
STABILITY
Critical Must-Knows
- Lateral aspect of medial femoral condyle is the most common location (75%) - classic site
- Juvenile (open physis) has significantly better prognosis than adult form
- Stable lesions in juveniles can heal conservatively with activity modification (50-70%)
- Unstable or adult lesions usually require surgery (drilling, fixation, or excision)
- MRI is gold standard to assess stability (fluid behind fragment = unstable)
Examiner's Pearls
- "Wilson sign: pain with IR at 90 then relieved with ER (impinges ACL on MFC)
- "Classic location: lateral aspect of MFC
- "T2 MRI shows fluid under fragment ('rim sign') = unstable
- "Juvenile stable: rest 3-6 months first line
Clinical Imaging
Imaging Gallery
Critical OCD Knee Concepts
Location
Lateral aspect of medial femoral condyle (75%). Other sites: lateral femoral condyle (20%), patella, trochlea, tibial plateau (rare). Classic location is PCL origin on MFC.
Juvenile vs Adult
Juvenile = open physis = better prognosis. Can heal with conservative treatment. Adult = closed physis = often needs surgery. Physis status is the most important prognostic factor.
Stability Assessment
MRI is key. High T2 signal behind fragment (rim sign) = fluid = unstable. Intact cartilage surface with no fluid = stable. Cystic changes = unstable.
Treatment Principle
Stable juvenile: conservative. Unstable or adult: surgery. Options include drilling (retrograde/transarticular), fixation (compression screws), or excision (if unsalvageable).
Osteochondritis Dissecans - Quick Decision Guide
| Type | Physis | Stability | Treatment | Prognosis |
|---|---|---|---|---|
| Juvenile Stable | Open | Stable | Conservative (3-6mo) | Good (50-70% heal) |
| Juvenile Unstable | Open | Unstable | Surgery (Fixation) | Good if fixed |
| Adult Stable | Closed | Stable | Surgery (Drilling/Fix) | Fair |
| Adult Unstable | Closed | Unstable | Surgery (Fix/Excision) | Poor (OA risk) |
MFCOCD Location
Memory Hook:MFC lateral wall is classic location!
FLUIDMRI Signs of Instability
Memory Hook:FLUID on MRI means unstable lesion!
VIAGRAOCD Etiology
Memory Hook:The etiology of OCD is multifactorial (VIAGRA).
DFSSurgical Indications
Memory Hook:Operate for DFS - Detached, Failed conservative, Skeletal maturity.
FIXTreatment Options
Memory Hook:FIX the fragment if possible!
Overview and Epidemiology
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
Classic Demographics
Active adolescent male. Most common presentation is a 10-20 year old male athlete with vague knee pain.
Epidemiology
- Incidence: 15-30 per 100,000
- Age: Juvenile (open physis) vs Adult (closed physis)
- Gender: Male > Female (2:1)
- Bilateral: 20-30% of cases (always xray other knee)
Pathophysiology and Mechanisms
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
- Subchondral Bone Event: Ischemia or stress fracture of subchondral bone
- Overlying Cartilage: Initially intact (stable)
- Separation: Bone fragment separates from parent bone
- Instability: Cartilage breach allows fluid ingress (unstable)
- Loose Body: Fragment detaches completely
Prognostic Factor
Physis Status: Open physis (Juvenile OCD) has much better healing potential due to vascularity. Closed physis (Adult OCD) rarely heals without intervention.
Classification Systems
Anatomic Location Classification
Location on Condyle:
- 1: Central
- 2: Lateral (Classic - aligned with tibial spine)
- 3: Inferocentral
- 4: Central anterior
- 5: Anterior lateral
Type 2 corresponds to the classic lateral aspect of MFC.
Location helps predict prognosis.
Clinical Assessment
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°
Wilson's Sign
Manoeuvre: Knee flexed 90°. Internally rotate tibia. Extend knee. Positive: Pain at ~30° flexion (tibial spine impinges on MFC lesion). Relief: External rotation relieves pain (moves spine away from lesion). Note: Classic sign, but notoriously unreliable.
Investigations
Plain Radiographs
Views: AP, Lateral, Tunnel (Notch), Skyline Findings:
- Tunnel view is most sensitive for classic MFC lesions
- Lucency: Crescent-shaped radiolucent area
- Sclerosis: Rim of sclerosis suggests chronicity
- Loose body: Calcified body in joint
- Physis: Check status (Open vs Closed)
X-rays are the initial screening tool.
Management Algorithm
OCD Management Pathway
Diagnose on X-ray/MRI. Determine if Juvenile (Open Physis) or Adult (Closed). Assess stability on MRI (Fluid signal).
If Juvenile + Stable: Activity modification (no impact) for 3-6 months. Serial X-ray/MRI. Success 50-70%.
If Unstable, Adult, or Failed Conservative: Surgery indicated. Assess fragment salvageability arthroscopically.
Good bone stock + cartilage: Preservation surgery. Retrograde drilling (stable), Screw/Pin Fixation (unstable).
Fragment necrotic/comminuted: Remove loose body. Perform Marrow Stimulation (Microfracture) or OATS/ACI for large defects.
Follow the pathway based on stability and physis status.
Surgical Technique
Retrograde Drilling
Indication: Stable lesion, failed conservative (usually Juvenile). Goal: Create vascular channels for healing without breaching cartilage. Technique:
- Fluoroscopic assistance
- K-wire drilled from extra-articular femur into the lesion
- Avoid penetrating articular surface
- Stimulates healing response
Drilling brings vascularity to the lesion.
Complications
| Complication | Risk | Prevention/Management |
|---|---|---|
| Non-healing | 30-50% in conservative | Select patients carefully, ensure compliance |
| Loose Body | If fragment detaches | Surgical removal |
| Osteoarthritis | Long-term risk | Preserve meniscus, restore articular surface |
| Hardware Issue | Prominent screws | Countersink well, use bioabsorbable |
Postoperative Care
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
Outcomes and Prognosis
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.
Evidence Base
Juvenile OCD Healing
- 50-67% healing rate with conservative care
- Predictors of failure: Size, Age, Patella
- 6 months duration required
Fixation Techniques
- 85% union rate with fixation
- Metal screws require removal
- Bioabsorbable avoids second surgery
Long-term OA Risk
- Long-term OA risk is elevated in all OCD
- Excision has highest risk
- Cartilage preservation is key
MRI Staging Accuracy for OCD
- MRI had 97% sensitivity for detecting unstable lesions
- T2 rim sign (fluid behind fragment) is most reliable instability marker
- Cartilage breach difficult to assess - 80% sensitivity
- Arthroscopy remains gold standard for cartilage assessment
Retrograde vs Transarticular Drilling
- Retrograde drilling preserves articular cartilage integrity
- Transarticular drilling violates cartilage surface but provides direct access
- Similar healing rates (78% vs 82%)
- Retrograde preferred for stable lesions with intact cartilage
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Juvenile Stable OCD
"A 13-year-old male football player presents with vague knee pain. X-ray shows a classic OCD lesion on the lateral MFC. Physes are wide open. MRI shows no fluid behind the fragment. How do you manage him?"
Scenario 2: Unstable Adult OCD
"A 25-year-old man presents with locking and catching. MRI shows a focal defect on the MFC with fluid behind a large osseous fragment. The cartilage hinge is intact on one side."
Scenario 3: Failed Conservative Juvenile
"The 13-year-old from the first scenario returns at 6 months. Despite strict compliance, he still has pain. MRI shows the lesion size is unchanged, but no fluid signal. What is your next step?"
MCQ Practice Points
Most Common Location
Q: What is the classic location of OCD knee? A: Lateral aspect of the Medial Femoral Condyle (75%). Often cited as the lateral wall of the intercondylar notch.
Prognosis
Q: What is the most significant prognostic factor? A: Status of the physis. Open physis (juvenile) has significantly better prognosis than closed physis (adult).
MRI Instability
Q: What MRI finding confirms instability? A: High T2 signal (fluid) behind the fragment. This is the 'rim sign', indicating fluid interposition and instability.
Wilson Sign
Q: What is the Wilson sign? A: Pain with internal rotation at 30 degrees flexion, relieved by external rotation. (Tibial spine impinges on MFC lesion).
Treatment
Q: Mechanism of retrograde drilling? A: Stimulates vascular access to the necrotic subchondral bone without breaching the overlying articular cartilage.
Australian Context
Incidence
- Common in Australian adolescent athletes (cricket, AFL, rugby)
- High index of suspicion required in 'knee pain' in 10-15yo
Referral Pathways
- Stable juvenile: Often managed by Sports Physician or Paediatric Ortho
- Unstable/Adult: Requires Orthopaedic Surgeon
- MRI accessible via Medicare (GP or Specialist)
OCD KNEE
High-Yield Exam Summary
Key Concepts
- •Lateral aspect of Medial Femoral Condyle (75%)
- •Juvenile (open physis) = Good prognosis
- •Adult (closed physis) = Poor prognosis
- •MRI Fluid behind fragment = Unstable
Classification
- •Juvenile Stable: Greater than 50% heal with rest
- •Juvenile Unstable: Fixation/Drilling
- •Adult: Almost always surgical
- •Stage III/IV: Unstable/Loose body
Treatment
- •Conservative: Activity mod 3-6mo (Juv Stable)
- •Drilling: Retrograde (Stable, failed conservative)
- •Fixation: Screw/Pin (Unstable, salvageable)
- •Excision: Loose body (Unsalvageable)
Imaging
- •X-ray: Tunnel view best for MFC
- •MRI: T2 Rim sign (Fluid) = Unstable
- •MRI: Assess cartilage integrity
- •Serial MRI: Follow healing
Clinical
- •Vague activity-related pain
- •Wilson Sign: Pain IR 30°, relieved ER
- •Mechanical symptoms = Instability
- •Antalgic gait (external rotation)