✅ Model Answer:
• Diagnosis: Legg-Calvé-Perthes disease (LCPD) — avascular necrosis of the femoral head. Age 4-8 (peak 6 years), male predominance, painless limp, limited hip abduction and internal rotation, normal inflammatory markers. X-ray shows flattening and sclerosis of the femoral head (coxa plana).
• Any other test: X-ray (AP & frog-leg) for flattening and sclerosis (Coxa plana), MRI (early diagnosis, assess extent of necrosis), bone age (for prognosis), Herring lateral pillar classification on X-ray to guide treatment.
• What to do next: Orthopedic referral. Containment treatment: bracing (Petrie cast, abduction orthosis) or femoral varus osteotomy if lateral pillar collapse (group B/C). Activity restriction to prevent weight-bearing stress.
• Follow-up plan: Monitor with serial X-rays (fragmentation → reossification → remodeling). Prognosis: better if age <6 and group A (lateral pillar >50%). Physical therapy for hip range of motion. Long-term monitoring for osteoarthritis.

✅ Model Answer:
• LCPD is a self-limited avascular necrosis of the femoral head (idiopathic). It is a developmental disorder of the hip.
• Pathophysiology: Disruption of blood supply to the femoral head → osteonecrosis → collapse → fragmentation → reossification → remodeling.
• Age: 4-8 years (peak 5-7 years).
• Gender: More common in boys (4-5:1).
• Race: More common in Caucasians.
• Bilateral: 10-15% (usually sequential, not simultaneous).
• Etiology: Unknown — may be related to trauma, thrombosis, or hypercoagulability.
• Prognosis: Depends on age of onset, extent of necrosis, and containment of the femoral head within the acetabulum.

✅ Model Answer:
• Classic presentation:
- Age: 4-8 years (most common).
- Painless limp: Often the only symptom — child limps without pain (or mild pain).
- Duration: Insidious onset (weeks to months).
- No fever or systemic symptoms.
- Limited range of motion: Especially abduction and internal rotation (due to muscle spasm).
- Antalgic gait: Painful limp (if pain is present).
- Trendelenburg gait: Due to abductor weakness.
- Shortened limb: May be present.
- Pain: May be referred to the knee or thigh.
• Stages: Initial (synovitis), fragmentation, reossification, and remodeling phases.

✅ Model Answer:
• X-ray (AP pelvis + frog-leg lateral):
- Initial (synovitis phase): May be normal or show subtle widening of the joint space (due to effusion).
- Fragmentation phase: Flattening of the femoral head (coxa plana), sclerosis (increased density), and irregularity of the epiphysis.
- Reossification phase: New bone formation, healing, and remodeling.
- Healed phase: Residual deformity: coxa magna (enlarged femoral head), coxa breva (short neck), and acetabular changes.
• Herring lateral pillar classification: Based on the height of the lateral pillar (lateral 1/3 of the femoral head) on the frog-leg lateral view:
- Group A: >50% height preserved → best prognosis.
- Group B: 50% height preserved → intermediate prognosis.
- Group C: <50% height preserved → worst prognosis (higher risk of deformity).
• MRI: Early diagnosis (shows bone marrow edema before X-ray changes).

✅ Model Answer:
• Containment treatment (goal): Keep the femoral head within the acetabulum to allow for spherical remodeling.
• Non-operative (conservative):
- Activity restriction: Avoid high-impact activities, jumping, running.
- Physical therapy: Maintain hip range of motion (abduction, internal rotation).
- Bracing: Abduction orthosis (Petrie cast or Scottish Rite orthosis) — used for younger children (age <6) or mild disease.
- Duration: Usually 1-2 years.
• Surgical (containment osteotomy):
- Indications: Older children (>6 years), Herring group B/C, or failure of conservative treatment.
- Procedures: Femoral varus osteotomy, pelvic osteotomy (Salter, Chiari, or triple osteotomy).
- Goal: Improve containment and prevent femoral head deformity.
• Follow-up: Serial X-rays every 3-6 months to monitor progression (fragmentation → reossification).

✅ Model Answer:
• Herring lateral pillar classification: Assesses the height of the lateral pillar (lateral 1/3 of the femoral head) on the frog-leg lateral X-ray during the fragmentation phase.
• Groups:
- Group A: Lateral pillar height is >50% of normal (best prognosis) — minimal collapse, good remodeling.
- Group B: Lateral pillar height is 50% of normal (intermediate prognosis) — some collapse, variable outcomes.
- Group C: Lateral pillar height is <50% of normal (worst prognosis) — significant collapse, high risk of residual deformity (coxa magna, coxa breva).
• Prognostic value:
- Group A: 95% good outcome (spherical femoral head).
- Group B: 70-80% good outcome.
- Group C: 50-60% good outcome (higher risk of osteoarthritis).
• Treatment implications:
- Group A: Usually treated conservatively (observation, bracing).
- Group B/C: Often require surgical containment (osteotomy) if age >6 years.

✅ Model Answer:
• Complications:
- Residual deformity: Coxa magna (enlarged femoral head), coxa breva (short femoral neck), coxa plana (flattened head).
- Leg length discrepancy: Due to growth disturbance.
- Premature osteoarthritis: Due to incongruity of the hip joint — most common long-term complication.
- Loss of hip range of motion: Stiffness, especially in abduction and internal rotation.
- Avascular necrosis: Already the underlying pathology; can progress if not contained.
- Femoroacetabular impingement (FAI): Due to residual deformity.
- Pain: Hip pain in adulthood.
- Prognosis: Worse with older age at onset (>8 years), Herring group C, and delayed treatment.
- Total hip replacement: May be needed in adulthood if severe osteoarthritis develops.

✅ Model Answer:
• Prognosis:
- Excellent: For children <6 years with Herring group A (95% good outcomes).
- Good: For children 6-8 years with Herring group A/B (70-80% good outcomes).
- Guarded: For children >8 years, Herring group C, or bilateral disease (higher risk of osteoarthritis).
- Natural history: The disease runs its course in 2-4 years (fragmentation → reossification → remodeling).
- Life expectancy: Normal.
• Long-term follow-up:
- Orthopedic: Follow-up X-rays every 6 months until healing is complete (skeletal maturity).
- Monitor for osteoarthritis: Long-term surveillance (clinical exams, X-rays).
- Physical therapy: Maintain hip range of motion, strengthen abductors.
- Activity modification: Avoid high-impact sports until healed.
- Radiographic monitoring: Assess for residual deformity (coxa magna, coxa breva) and joint space narrowing.
- Future: Risk of premature osteoarthritis — may require hip replacement in adulthood (usually 40-60 years).