✅ Model Answer:
• Diagnosis: Slipped Capital Femoral Epiphysis (SCFE) — obese adolescent (BMI 32), referred knee pain (a classic presentation), limp, normal inflammatory markers, AP pelvis X-ray appears normal. The pain in the knee is referred from the hip. Frog-leg lateral view is required to confirm the diagnosis (Klein's line does not intersect the epiphysis).
• Any other test: Frog-leg lateral X-ray (Klein's line sign — loss of intersection with the lateral femoral head), radiograph of the contralateral hip (20-40% bilateral involvement), thyroid panel (hypothyroidism can predispose), renal function (if secondary cause suspected).
• What to do next: Admit for non-weight-bearing. Urgent orthopedic referral. In situ pinning (single percutaneous screw) to prevent further slip and avascular necrosis.
• Follow-up plan: Monitor for contralateral slip (20-40% risk). Post-operative weight-bearing restrictions. Long-term: monitor for avascular necrosis, chondrolysis. Avoid high-impact activities until healed.

✅ Model Answer:
• SCFE is a displacement of the femoral head relative to the femoral neck through the proximal femoral physis (growth plate).
• Pathophysiology: The femoral head slips posteriorly and inferiorly relative to the neck (the epiphysis remains in the acetabulum).
• Age: Most common in adolescents during the growth spurt (10-16 years).
• Gender: More common in boys (2:1).
• Risk factors:
- Obesity (most common — mechanical overload on the physis).
- Endocrine disorders: Hypothyroidism, growth hormone excess, hypogonadism.
- Renal osteodystrophy (secondary hyperparathyroidism).
- Previous radiation therapy to the hip.
• Bilateral: 20-40% have bilateral involvement (often sequential).
• Classification:
- Stable: Can bear weight with crutches.
- Unstable: Cannot bear weight (even with crutches) — higher risk of avascular necrosis.

✅ Model Answer:
• Classic presentation:
- Adolescent (10-16 years), often obese.
- Referred knee pain: Pain in the knee (due to obturator nerve referral) — a classic presentation.
- Limp: Antalgic gait (painful limp).
- No fever (afebrile).
- Normal inflammatory markers (WBC, ESR, CRP).
• Physical exam findings:
- Limited internal rotation: Most sensitive finding — the hip externally rotates when flexed (obligate external rotation).
- Pain on passive internal rotation of the hip.
- Shortened limb (if slipped).
- Antalgic gait (limp).
- Drehmann sign: External rotation of the hip with flexion.
• Red flags: Bilateral symptoms, endocrine abnormalities (short stature, delayed puberty).

✅ Model Answer:
• X-ray (AP pelvis + frog-leg lateral):
- AP view: May show subtle findings: widening of the physis, decreased epiphyseal height, or Klein's line (a line drawn along the superior femoral neck) — normally intersects the epiphysis; in SCFE, it does not intersect.
- Frog-leg lateral view: The gold standard for diagnosing SCFE — shows posterior and inferior displacement of the epiphysis relative to the metaphysis.
- If AP is normal: Frog-leg lateral must be done (as in this case, AP was normal).
• Other findings:
- Blanch sign: Increased density of the metaphysis (due to bone remodeling).
- Periosteal new bone formation (chronic slips).
- Contralateral hip: Should be imaged (20-40% bilateral).
• If X-ray is normal but clinical suspicion is high: Consider MRI (shows physeal widening and edema).

✅ Model Answer:
• Urgent orthopedic consultation: SCFE is a surgical emergency.
• Non-weight-bearing: The patient should be kept non-weight-bearing until surgery (to prevent further slip).
• Surgical treatment:
- In situ pinning: A single percutaneous screw across the physis to prevent further slip. This is the standard of care for stable and unstable SCFE.
- Avoid reduction: Attempting to reduce the slip increases the risk of avascular necrosis.
- Contralateral side: Prophylactic pinning may be considered if the contralateral hip is at high risk (obesity, endocrine disorder).
• Post-operative: Partial weight-bearing for 6-8 weeks, then progressive weight-bearing.
• Endocrine evaluation: If bilateral, young age (<10 years), or short stature → evaluate for hypothyroidism, growth hormone excess, or renal disease.

✅ Model Answer:
• Complications:
- Avascular necrosis (AVN) of the femoral head: Most serious complication — occurs in 10-30% of unstable SCFE (higher if reduction is attempted or if diagnosis is delayed).
- Chondrolysis: Acute cartilage necrosis leading to joint space narrowing, stiffness, and pain. Occurs in 5-10% of patients.
- Contralateral slip: 20-40% of patients develop SCFE on the other side (especially in obese adolescents).
- Femoroacetabular impingement (FAI): Due to residual deformity → may cause hip pain in adulthood.
- Premature osteoarthritis: Long-term consequence of residual deformity or AVN.
- Growth disturbance: Leg length discrepancy.
- Death: Rare, but can occur from complications of surgery (pulmonary embolism, infection).

✅ Model Answer:
• Endocrine evaluation: Indicated in the following scenarios:
- Age <10 years (early onset).
- Bilateral SCFE (especially if sequential).
- Short stature or delayed puberty.
- Associated features: Obesity, hypogonadism, or other endocrine signs.
• Tests:
- Thyroid function: TSH, free T4 (hypothyroidism is a known predisposing factor).
- Growth hormone: IGF-1, IGFBP-3 (growth hormone excess can cause SCFE).
- Renal function: BUN, creatinine, calcium, phosphorus, PTH (renal osteodystrophy).
- Vitamin D: Deficiency may contribute.
- Testosterone/estradiol: For pubertal assessment.
• If an underlying endocrine disorder is found: Treat the underlying condition to prevent progression and recurrence.

✅ Model Answer:
• Prognosis:
- Good: For stable SCFE with early diagnosis and in situ pinning (minimal long-term sequelae).
- Guarded: For unstable SCFE (higher risk of AVN and chondrolysis).
- Avascular necrosis: Occurs in 10-30% of unstable slips → may lead to early osteoarthritis and need for hip replacement.
- Contralateral slip: 20-40% risk — requires monitoring.
- Chondrolysis: May cause permanent joint stiffness and pain.
- Life expectancy: Normal.
• Long-term follow-up:
- Orthopedic: Follow-up X-rays at 6 months, 1 year, and then as needed.
- Monitor for AVN: X-ray changes (femoral head collapse, sclerosis).
- Monitor for contralateral slip: Inform parents about warning signs (new limp, knee pain).
- Activity modification: Avoid high-impact sports until skeletal maturity.
- Weight management: Important to reduce risk of contralateral slip.
- Endocrine follow-up: If an underlying condition is identified.