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Difficulty: EasyOrthopedic Surgery

An overweight 13-year-old boy is brought to the outpatient clinic by his parents. He has been complaining of left knee and anterior thigh pain for the past four weeks. The pain is described as a dull ache that worsens with physical activity such as walking or climbing stairs. There is no history of recent trauma, falls, or fever. His temperature is 36.8°C (98.2°F), blood pressure is 112/72 mm Hg, pulse is 76/min, and respirations are 14/min. His body mass index is 31 kg/m². Upon physical evaluation, the left knee shows no evidence of erythema, swelling, or localized tenderness, and ligamentous testing is normal. However, examination of the left hip reveals restricted internal rotation. Furthermore, when the clinician passively flexes the patient's left hip, the thigh obligatorily rotates outward. Motor strength and sensory examinations in the lower extremities are unremarkable. Distal pulses are palpable and equal bilaterally.

Which of the following is the most appropriate next step in management?

  1. Bilateral anteroposterior and frog-leg lateral pelvic radiographsAnswer
  2. B
    Magnetic resonance imaging of the left knee joint
  3. C
    Reassurance and outpatient weight management counseling
  4. D
    Intravenous administration of broad-spectrum antibiotics
  5. E
    Immediate diagnostic arthrocentesis of the left knee

Answer

Bilateral anteroposterior and frog-leg lateral pelvic radiographs
The correct answer is bilateral anteroposterior and frog-leg lateral pelvic radiographs. This patient's presentation—an obese adolescent boy with atraumatic, chronic knee/thigh pain and limited internal rotation of the hip—is a classic textbook description of Slipped Capital Femoral Epiphysis (SCFE). Because the obturator nerve provides sensory innervation to both the hip and the knee, hip pathology frequently presents solely as referred knee pain. The physical exam finding of obligatory external rotation during passive hip flexion is a hallmark, pathognomonic sign of SCFE. The next best step to confirm this diagnosis is obtaining AP and frog-leg lateral radiographs of both hips, as the condition is often bilateral and requires urgent surgical pinning.

Step-by-Step Solution

1
Analyze the patient's demographics and chief complaint.
An obese adolescent boy presents with chronic, atraumatic left knee and thigh pain.
Identifying the epidemiological profile (obese adolescent) helps narrow down the differential diagnosis for pediatric joint pain.
2
Correlate the symptoms with the physical examination findings.
The knee exam is entirely normal, but the hip exam shows restricted internal rotation and obligatory external rotation with hip flexion.
Because the obturator nerve innervates both the hip and the knee, hip pathology frequently presents solely as referred knee pain.
3
Identify the most likely diagnosis based on the clinical picture.
The combination of obesity, adolescent age, referred knee pain, and classic hip examination findings is highly suspicious for Slipped Capital Femoral Epiphysis (SCFE).
SCFE is characterized by posterior and inferior displacement of the proximal femoral epiphysis, leading to the classic sign of obligatory external rotation.
4
Determine the appropriate initial diagnostic test.
Bilateral anteroposterior and frog-leg lateral radiographs of the pelvis are required.
These specific X-ray views are the standard initial modality to visualize and confirm the epiphyseal displacement in SCFE.

Key Concept

Diagnosis of Slipped Capital Femoral Epiphysis (SCFE) through identification of referred knee pain and appropriate hip imaging.
Estimated Time:1m 0s
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Topics

Orthopedic Surgery

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