# CIM Case: Knee OCD - Skeletally Immature ## Clinical Scenario **Patient:** 12-year-old male **Presentation:** 6-month history of anterior knee pain worsened by activity, occasional locking and giving way **Relevant history:** Active sportsman playing football and basketball, no previous knee injuries, pain started insidiously, now limiting sport, occasional swelling after activity **Examination findings:** - Mild effusion - Tenderness over medial femoral condyle (palpable with knee flexed 90°) - Wilson test positive (pain with internal rotation during extension 90° to 30°, relieved by external rotation) - Full range of motion - No ligamentous laxity - No meniscal signs - Normal alignment - Neurovascularly intact --- ## Investigations Provided ### Laboratory Results | Test | Result | Normal Range | Interpretation | |------|--------|--------------|----------------| | N/A | - | - | Bloods not routinely required for OCD | ### Imaging **Image 1: AP, Lateral, and Tunnel View (Notch View) Knee Radiographs** **Radiological features:** - Well-circumscribed lucent lesion on lateral aspect of medial femoral condyle - Lesion size approximately 15mm × 12mm - Sclerotic margin visible - No loose body in joint - Physes open (skeletally immature) - No evidence of fragmentation on X-ray - Classic location for OCD **Image 2: MRI Knee** **MRI findings:** - 15mm lesion on lateral aspect of medial femoral condyle (classic location) - T2-weighted: High signal rim behind fragment (fluid signal) - Subchondral cysts visible - Articular cartilage disrupted (not intact) - Fragment appears in situ but unstable - No displaced loose body - Minimal joint effusion ## Questions & Model Answers **Stability Assessment - Critical for Management:** **Clinical Features of Instability:** - Mechanical symptoms (locking, catching, giving way) - Effusion - Loose body palpable or visible on imaging **MRI Criteria for Instability (Most Important):** | MRI Finding | Significance | |-------------|--------------| | **T2 hyperintense rim** | Fluid behind fragment = unstable | | **Subchondral cysts** | Suggests instability | | **Cartilage breach** | Surface disruption = unstable | | **Fragment displacement** | Definitely unstable | | **High signal in fragment** | Suggests necrosis | **Arthroscopic Assessment (Definitive):** - Probe fragment under direct vision - Assess cartilage integrity - Check for hinge/flap pattern - Definitive stability assessment **Classification Systems:** **MRI-Based (Kocher/DiPaola):** | Grade | Description | Stability | |-------|-------------|-----------| | **I** | Thickening/signal change, intact cartilage | Stable | | **II** | Breach of cartilage, no fluid | Stable/borderline | | **III** | Fluid behind fragment (T2 rim sign) | Unstable | | **IV** | Loose body | Unstable | **Arthroscopic (ICRS):** | Grade | Description | |-------|-------------| | **I** | Softening/blister, cartilage intact | | **II** | Partial discontinuity, stable | | **III** | Complete discontinuity, fragment in situ | | **IV** | Displaced fragment/loose body | **This Patient:** MRI shows T2 signal behind fragment with cartilage disruption = UNSTABLE (Grade III). Despite juvenile OCD, surgery is indicated. > **Consultant Tip:** The T2 rim sign is the most reliable MRI indicator of instability. If you see fluid behind the fragment, it's unstable regardless of other factors. **Juvenile vs Adult OCD:** | Feature | Juvenile OCD | Adult OCD | |---------|--------------|-----------| | **Definition** | Open physes | Closed physes | | **Age range** | <14 girls, <16 boys (typically) | After physeal closure | | **Healing potential** | High (growing cartilage/bone) | Lower | | **Non-operative success** | 50-94% for stable lesions | Rarely successful | | **Surgical success** | >90% for fixation | 70-85% for fixation | | **OA development** | Lower if treated early | Higher risk | **Why Juvenile OCD Has Better Prognosis:** 1. Active physeal growth enhances bone healing 2. Cartilage regenerative capacity higher in children 3. Subchondral vascular supply more robust 4. Remodelling potential exists **Prognostic Factors in Juvenile OCD:** | Factor | Better Prognosis | Worse Prognosis | |--------|------------------|-----------------| | **Skeletal maturity** | Open physes, younger | Near skeletal maturity | | **Lesion location** | Classic (lateral MFC) | Atypical (trochlea, patella) | | **Lesion size** | Smaller (<15mm) | Larger (>20mm) | | **Stability** | Stable | Unstable | | **Fragment quality** | Intact cartilage | Fragmented, poor cartilage | **This Patient:** 12-year-old male with open physes = JUVENILE OCD. However, the lesion is unstable (T2 rim sign, cartilage breach). Despite favourable age, the instability means surgery is needed - non-operative management will fail. **Key Point:** "Window of opportunity" exists in juvenile OCD. Early treatment before skeletal maturity optimises outcomes. Delays allow progression and reduce healing potential. > **Consultant Tip:** Don't assume all juvenile OCD can be treated non-operatively. Stability, not age, determines management. An unstable juvenile lesion needs surgery. **Indications for Non-operative Management:** - Stable lesion (no T2 rim sign, intact cartilage) - Juvenile OCD (open physes) - Small to moderate size - Compliant patient and family **Non-operative Protocol:** **Phase 1: Activity Modification (6-12 weeks)** - Complete cessation of sport - Non-weight-bearing or touch weight-bearing with crutches (6 weeks) - May use hinged knee brace locked in extension for protection - Avoid impact loading, squatting, kneeling **Phase 2: Protected Rehabilitation (6-12 weeks)** - Progress to partial then full weight-bearing - Low-impact activities (swimming, cycling) - Physiotherapy for quadriceps/hamstring strengthening - ROM exercises - Continue sport restriction **Monitoring Protocol:** | Time | Assessment | |------|------------| | 6 weeks | Clinical review, X-ray | | 3 months | Clinical review, X-ray (MRI if not improving) | | 6 months | X-ray (MRI to assess healing) | | 12 months | Final assessment | **Indicators of Healing:** - Resolution of symptoms - X-ray: Increased sclerosis, lesion filling in - MRI: Resolution of T2 signal, subchondral bone restoration **Indicators of Failure:** - Persistent symptoms beyond 3-6 months - No radiographic improvement - Development of mechanical symptoms - MRI showing progression or new instability signs **Expected Outcomes:** - Stable juvenile OCD: 50-94% healing with non-operative treatment - Average healing time: 6-18 months - Compliance is critical for success **This Patient:** NOT a candidate for non-operative management. The T2 rim sign indicates instability - non-operative treatment will fail. Surgery is needed. > **Consultant Tip:** Compliance is the biggest challenge with non-operative OCD management. A 12-year-old footballer will struggle to avoid sport for 6 months. Set expectations clearly. **Surgical Goal:** Preserve native cartilage and promote healing **Decision Tree for Unstable Juvenile OCD:** ``` Unstable Lesion │ ▼ Arthroscopic Assessment │ ├─ Fragment Salvageable → Fragment Fixation │ (Good cartilage, (Screws, K-wires, │ adequate bone) bone pegs) │ └─ Fragment Not Salvageable │ ├─ Small (<1.5cm) → Microfracture/Drilling │ └─ Large (>1.5cm) → OATS or ACI ``` **Option 1: Drilling (Trans-articular or Retroarticular)** | Indication | Technique | |------------|-----------| | Intact cartilage but T2 signal behind | Promotes vascular ingrowth | | Early instability | Multiple 1.5mm K-wire passes | - Retroarticular drilling preserves articular surface (fluoroscopy-guided) - Trans-articular drilling through softened cartilage **Option 2: Fragment Fixation (First Choice if Salvageable)** | Fixation Type | Advantages | Disadvantages | |---------------|------------|---------------| | **Bioabsorbable screws/pins** | No hardware removal | May cause reaction | | **Headless compression screws** | Strong fixation | May need removal | | **Bone pegs (autologous)** | Biological, no hardware | Donor site morbidity | | **K-wires** | Simple | May need removal | **Technique:** 1. Arthroscopic assessment and debridement of bed 2. Curette bed to bleeding bone 3. May add bone graft under fragment 4. Reduce and fix with chosen device 5. Countersink hardware below cartilage level **Option 3: Microfracture** | Indication | Technique | |------------|-----------| | Small unsalvageable lesion (<1-1.5cm) | Awl holes 3-4mm apart, 4mm deep | | Poor fragment quality | Creates fibrocartilage | **Option 4: OATS (Osteochondral Autograft Transfer)** | Indication | Technique | |------------|-----------| | Larger defects (1.5-4cm²) | Single plug or mosaicplasty | | Failed other treatments | Harvest from non-weight-bearing area | | Good bone stock in recipient | Medial trochlear ridge or lateral condyle | **Option 5: ACI (Autologous Chondrocyte Implantation)** | Indication | Notes | |------------|-------| | Large defects (>2-4cm²) | Two-stage procedure | | Failed other treatments | Expensive, prolonged recovery | **This Patient:** Arthroscopy with assessment of fragment. If cartilage quality good and fragment substantial → fixation with bioabsorbable screws. If fragment not salvageable → microfracture (if small) or OATS (if larger). > **Consultant Tip:** Always try to save the native fragment first. Bioabsorbable pins avoid a second operation for hardware removal. **Surgical Technique: Arthroscopic OCD Fragment Fixation** **Setup:** - Supine with leg holder or lateral post - Tourniquet on thigh - Standard anterolateral and anteromedial portals - Consider accessory portal for instrumentation **Step 1: Diagnostic Arthroscopy** - Systematic examination of all compartments - Assess lesion location, size, stability - Probe fragment - determine if salvageable - Document cartilage quality **Step 2: Prepare the Fragment and Bed** | Step | Technique | |------|-----------| | **Lift fragment** | Use probe or curette to hinged open | | **Debride bed** | Remove fibrous tissue | | **Curette to bleeding** | Fresh cancellous bone should be visible | | **Assess fragment underside** | Debride dead bone, leave cartilage | **Step 3: Bone Grafting (Optional but Recommended)** - Pack autologous bone graft under fragment - Source: Gerdy's tubercle or tibial tunnel - Alternatively: bone graft substitute - Improves fragment incorporation **Step 4: Reduce Fragment** - Replace fragment into bed - Ensure flush with surrounding cartilage - Check congruity with probe **Step 5: Fixation** **Bioabsorbable Screw Technique:** 1. Drill guide wire through fragment into condyle (perpendicular to articular surface) 2. Measure depth 3. Overdrill for screw (leave 5mm bone bridge) 4. Insert bioabsorbable screw (countersink below cartilage) 5. Use 2 screws minimum for rotational stability 6. Confirm position and stability **Headless Compression Screw Technique:** - Herbert or Acutrak screw - Self-drilling/tapping - Countersink 2-3mm below surface - Consider future arthroscopy for removal **Bone Peg Technique:** - Harvest osteochondral plug from non-weight-bearing area - Use core to create peg - Insert through fragment into bed - No hardware to remove **Step 6: Final Checks** - Confirm fixation is secure - Take knee through ROM - Check hardware not proud - Document with photos/video **Postoperative Protocol:** | Phase | Duration | Activity | |-------|----------|----------| | **1** | 0-6 weeks | NWB, ROM brace, gentle flexion | | **2** | 6-12 weeks | PWB → FWB, advance ROM | | **3** | 3-6 months | Strengthening, cycling, swimming | | **4** | 6-12 months | Return to sport | > **Consultant Tip:** The key to successful fixation is preparing a healthy bleeding bed. Dead bone won't incorporate - curette until you see punctate bleeding. **Complications of OCD Surgery:** **Early Complications:** | Complication | Incidence | Management | |--------------|-----------|------------| | **Infection** | 1-2% | Arthroscopic washout, antibiotics | | **Haemarthrosis** | 5-10% | Aspiration if tense | | **DVT** | Rare in children | Prophylaxis not routine | | **Stiffness** | 5% | Physiotherapy, may need MUA | **Late Complications:** | Complication | Incidence | Notes | |--------------|-----------|-------| | **Failure of fixation** | 10-20% | May need revision or alternative | | **Nonunion** | 10-15% | Revision fixation or cartilage restoration | | **Hardware prominence** | 10-20% | Removal of metallic hardware | | **Progression to OA** | Variable | Higher if untreated or delayed | | **Donor site morbidity** (OATS) | 5-10% | Pain, cartilage damage at harvest | **Expected Outcomes by Treatment:** | Treatment | Success Rate (Juvenile) | Notes | |-----------|------------------------|-------| | **Non-operative (stable)** | 50-94% | Compliance critical | | **Drilling** | 75-90% | For stable with T2 changes | | **Fragment fixation** | 85-95% | Best for salvageable fragments | | **Microfracture** | 70-85% | Fibrocartilage, not hyaline | | **OATS** | 80-90% | Good for contained defects | | **ACI** | 75-90% | Large defects, prolonged recovery | **Return to Sport Protocol:** **Criteria-Based Progression (NOT Time-Based):** | Milestone | Criteria | |-----------|----------| | **Jogging** | No pain, no effusion, 80% quad strength | | **Running** | No pain with jogging, single leg hop equal | | **Sport-specific** | Equal strength, no symptoms | | **Competition** | Pass functional testing battery | **Typical Timeline:** | Activity | Timeline | |----------|----------| | **Walking** | 6-12 weeks | | **Cycling/Swimming** | 8-12 weeks | | **Jogging** | 4-6 months | | **Running** | 5-7 months | | **Sport** | 6-9 months | | **Competition** | 9-12 months | **For This Patient:** - Fixation success rate ~90% - Full healing expected given open physes - Return to football: 9-12 months minimum - Long-term prognosis excellent if fragment heals **Factors for Better Outcome:** - Younger age (open physes) - Early intervention - Stable fixation - Compliance with rehabilitation **Factors for Worse Outcome:** - Delayed treatment - Large lesion - Poor fragment quality - Non-compliance > **Consultant Tip:** Return to sport is based on criteria, not calendar. A 12-year-old may push for early return - resist this. Premature loading risks fixation failure. --- ## Key Teaching Points ### Pattern Recognition **This pattern suggests Juvenile OCD:** - Adolescent with activity-related knee pain - Pain localised to medial femoral condyle - Positive Wilson test (specific but not sensitive) - Effusion with activity - X-ray: Lesion on lateral aspect of medial femoral condyle - Open physes **Classic OCD Location:** | Location | Percentage | Notes | |----------|------------|-------| | Lateral MFC (classic) | 70% | Most common | | Central MFC | 15% | | | Lateral femoral condyle | 10% | | | Trochlea/Patella | 5% | Atypical, worse prognosis | **Wilson Test:** - Patient extends knee from 90° to 30° with tibia internally rotated - Pain reproduced as tibial spine impinges on OCD lesion - Relief with external rotation - Specific but not sensitive (many false negatives) ### Critical Management Points 1. **Stability determines management** - not age alone 2. **T2 rim sign on MRI = unstable** - needs surgery regardless of age 3. **Juvenile OCD has better prognosis** - but unstable still needs surgery 4. **Save native fragment if possible** - bioabsorbable fixation preferred 5. **Prepare bed to bleeding bone** - key to healing 6. **Compliance is critical** - set expectations with family 7. **Criteria-based return to sport** - not calendar-based --- ## Common Examiner Follow-ups **Q: "What is the Wilson test and how does it work?"** The Wilson test is specific for medial femoral condyle OCD: - Mechanism: The tibial eminence impinges on the lateral aspect of the medial femoral condyle during knee extension with internal rotation - Positive test: Pain at 30° flexion (where OCD lesion is contacted) that resolves with external rotation - Sensitivity: Low (30-50%) - Specificity: High (80-90%) A negative Wilson test does NOT exclude OCD. The test is useful when positive but cannot be used to rule out the condition. --- **Q: "What if the fragment falls into the joint during fixation?"** Intraoperative fragment displacement: 1. Don't panic - this is manageable 2. Retrieve the fragment (loose body grasper) 3. Assess quality - can it still be salvaged? 4. If yes: - Debride both surfaces - Bone graft the bed - Fix in place 5. If no (fragmented, poor cartilage): - Remove fragment - Prepare bed - Microfracture if small - OATS if large - Consider staged ACI if very large --- **Q: "What is retroarticular drilling?"** Retroarticular drilling is a technique to promote healing of OCD without violating the articular cartilage: **Technique:** - Done under fluoroscopic guidance - Drill from outside the joint (extraarticular) into the subchondral bone of the OCD lesion - Penetrate the sclerotic zone without breaching the cartilage surface - Creates channels for vascular ingrowth from healthy bone - Used for stable lesions with intact cartilage but concerning MRI appearance **Advantages:** - Preserves articular surface completely - Promotes biological healing - Minimally invasive **Disadvantages:** - Requires fluoroscopy - May not be sufficient for unstable lesions --- **Q: "When would you use OATS versus ACI?"** | Factor | OATS | ACI | |--------|------|-----| | **Defect size** | 1-4 cm² | >2-4 cm² | | **Procedures** | Single stage | Two-stage | | **Cartilage type** | Hyaline | Hyaline (newer) | | **Cost** | Lower | Higher | | **Donor morbidity** | Yes (harvest site) | Minimal | | **Recovery** | 6-9 months | 9-12 months | **General Approach:** - Small defects (<1.5cm): Microfracture - Medium defects (1.5-4cm): OATS - Large defects (>4cm): ACI or OATS mosaicplasty - Very large defects: ACI preferred (no donor site issue) --- ## Related Topics - Patellar Instability - Meniscal Tears - ACL Injuries in Children - Tibial Spine Fractures - Knee Arthroscopy - Cartilage Restoration