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Difficulty: Very hardOrthopedic Surgery

A 13-year-old boy is brought to the emergency department by his parents due to severe right-sided leg pain. For the past month, he has complained of a dull, intermittent ache in his right anterior thigh and knee, which he attributed to playing basketball. This morning, while walking down the stairs, he felt a sudden "pop" and experienced exquisite pain. He is now completely unable to bear weight on the right leg. His body mass index is 33 kg/m233 \text{ kg/m}^2. Vital signs are within normal limits, and he is afebrile. Physical examination reveals a well-appearing boy in moderate discomfort. Inspection of the right knee shows no swelling, erythema, or localized tenderness. When the examiner attempts to passively flex the right hip to 90∘90^\circ, the thigh obligately rotates externally. There is significantly limited internal rotation of the right hip compared to the left. Which of the following is the most appropriate next step in management?

  1. A
    Obtain magnetic resonance imaging of the right knee
  2. B
    Admit the patient for strict bed rest and administration of nonsteroidal anti-inflammatory drugs
  3. Obtain anteroposterior and cross-table lateral radiographs of the bilateral hipsAnswer
  4. D
    Perform an ultrasound of the right hip and initiate empiric intravenous antibiotics
  5. E
    Obtain anteroposterior and frog-leg lateral radiographs of the bilateral hips

Answer

Obtain anteroposterior and cross-table lateral radiographs of the bilateral hips
This patient's presentation is classic for an unstable slipped capital femoral epiphysis (SCFE). SCFE typically occurs in obese adolescents and presents with dull hip, thigh, or knee pain (referred via the obturator nerve). The physical exam finding of obligate external rotation during passive hip flexion is pathognomonic. Crucially, this patient's condition recently transitioned from stable to unstable, defined clinically by the inability to bear weight. In unstable SCFE, the standard frog-leg lateral radiograph is strictly contraindicated because placing the leg in that position can cause further epiphyseal slip and significantly increase the risk of avascular necrosis of the femoral head. Therefore, the correct approach is to obtain an anteroposterior view and a cross-table lateral view, which provides a lateral profile of the proximal femur without requiring manipulation of the injured leg.

Step-by-Step Solution

1
Analyze the clinical presentation and physical exam findings.
The patient has an elevated BMI, chronic preceding knee/thigh pain, sudden worsening, obligate external rotation with hip flexion, and inability to bear weight.
These findings are pathognomonic for a Slipped Capital Femoral Epiphysis (SCFE). The chronic knee pain is referred via the obturator nerve.
2
Determine the stability of the condition.
The patient is completely unable to bear weight on the affected extremity.
Inability to bear weight classifies the SCFE as 'unstable,' which carries a much higher risk of avascular necrosis and further displacement.
3
Select the appropriate diagnostic imaging based on stability.
Anteroposterior and cross-table lateral radiographs must be ordered.
Frog-leg lateral views require external rotation and abduction of the hip, which can cause iatrogenic further slipping in an unstable SCFE. A cross-table lateral view evaluates the hip without requiring dangerous manipulation.

Key Concept

Diagnosis and appropriate imaging selection for stable versus unstable Slipped Capital Femoral Epiphysis (SCFE).
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Topics

Orthopedic Surgery

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