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Difficulty: Very hardPediatric Musculoskeletal Disorders

A 13-year-old boy is brought to the emergency department after experiencing a sudden, severe "pop" and excruciating pain in his left groin while playing basketball. He was unable to continue playing and had to be carried off the court. Over the preceding 8 weeks, he had been complaining of intermittent, mild aching in his left anterior thigh, which he attributed to a muscle strain. He is currently unable to bear any weight on the left leg. On physical examination, his body mass index is 31 kg/m². The left lower extremity is shortened and held in an externally rotated position. Passive range of motion of the left hip is exquisitely painful and globally restricted. Anteroposterior and frog-leg lateral radiographs of the pelvis demonstrate posterior and inferior displacement of the left proximal femoral epiphysis relative to the metaphysis. Compared to his clinical status yesterday, the acute event that occurred today has most significantly increased his risk for developing which of the following complications?

  1. A
    Contralateral epiphyseal displacement
  2. B
    Chondrolysis of the hip joint
  3. Osteonecrosis of the femoral headAnswer
  4. D
    Premature degenerative joint disease
  5. E
    Fat embolism syndrome

Answer

Osteonecrosis of the femoral head
This patient's presentation of a sudden inability to bear weight, following weeks of prodromal pain, defines an unstable slipped capital femoral epiphysis (SCFE). In an unstable SCFE, the acute mechanical shearing of the physis frequently stretches or tears the retinacular vessels (branches of the medial circumflex femoral artery) that supply the femoral head. Consequently, the most significant risk associated with this acute transition is osteonecrosis (avascular necrosis), the incidence of which jumps from under 5% in stable slips to up to 50% in unstable slips.

Step-by-Step Solution

1
Analyze the patient's presentation and history.
13-year-old obese male with 8 weeks of prodromal thigh pain and a sudden inability to bear weight after a pop in the groin.
Identifies the underlying condition and its acuity.
2
Synthesize clinical and radiographic findings to make a specific diagnosis.
Diagnosis is an unstable slipped capital femoral epiphysis (SCFE).
The history of a pop and new inability to bear weight indicates an acute-on-chronic slip; inability to ambulate defines it as 'unstable'.
3
Differentiate the complication profiles between stable and unstable SCFE.
Unstable SCFE has a vastly higher rate of avascular necrosis (osteonecrosis) compared to stable SCFE.
The acute physeal separation in an unstable slip frequently stretches or tears the delicate retinacular blood vessels supplying the femoral epiphysis, leading to ischemia.

Key Concept

The transition from a stable to an unstable slipped capital femoral epiphysis (defined by the inability to bear weight) dramatically increases the risk of osteonecrosis of the femoral head due to disruption of the retinacular blood supply.
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Topics

Pediatric Musculoskeletal Disorders

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