A 13-year-old boy is brought to the emergency department due to refusal to bear weight on the right leg. He has had vague right knee pain for the last 4 days that is now localized to his proximal thigh. Today, the pain has worsened and he is unable to bear weight. The boy has also had a decreased appetite and high fever for the last 3 days. He has had no recent trauma. The patient has no known medical conditions and has had no surgeries. Weight is >95th percentile, height is at the 25th percentile, and BMI is >95th percentile. Palpation over the anterior femur elicits point tenderness. Bilateral hips have full range of motion. The skin overlying the right proximal femur is slightly swollen and erythematous. The remainder of the examination is normal. Which of the following best describes the pathogenesis of this patient's current condition?
Osteomyelitis in children | |
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CRP = C-reactive protein; ESR = erythrocyte sedimentation rate; WBC = white blood cell. | |
This patient's fever, leg pain, and refusal to bear weight are concerning for acute osteomyelitis. Although trauma (eg, surgery, injury) can sometimes introduce infection to bone, in children osteomyelitis is most commonly caused by hematogenous spread. Bacteria (typically Staphylococcus aureus) travel through the bloodstream and seed the well-vascularized metaphysis of long bones (eg, femur), resulting in focal bone marrow infection. Inflammation compromises blood flow, allowing the infection to penetrate the bony cortex and cause necrosis.
Signs of bony inflammation include fever and pain (which may initially be referred to the knee) as well as swelling, erythema, and point tenderness over the affected area. Inflammatory markers are typically elevated and blood culture can help determine the infectious etiology. Radiographs may be normal initially or reveal periosteal elevation (due to subcortical purulence) or cortical thickening. Although inflammation on MRI typically confirms the diagnosis, biopsy and culture of the infected bone is the gold standard for diagnosis. Treatment is with antistaphylococcal antibiotics (eg, vancomycin).
(Choice A) Avascular necrosis of the femoral head, or Legg-Calvé-Perthes disease, presents with chronic hip (or referred knee) pain and a limp. Patients are afebrile and have limited range of motion of the hip without soft-tissue swelling on examination.
(Choice B) Decreased mineralization of bone is seen in rickets and can lead to generalized, chronic bone pain and bowing. Patients are at increased risk for fracture, not osteomyelitis.
(Choice C) Displacement of the proximal femoral physis occurs in slipped capital femoral epiphysis, which presents in obese adolescent boys with chronic dull hip (or referred knee) pain and a limp. Patients are afebrile with limited internal rotation of the hip on examination.
(Choice E) Ewing sarcoma is a malignant degeneration of bone commonly found in the femoral diaphysis. Findings include localized pain and swelling; however, symptoms typically present over weeks to months and are often worse at night.
Educational objective:
Pediatric acute osteomyelitis is most commonly caused by hematogenous spread of bacteria to the metaphysis of long bones. Patients have fever, refusal to bear weight, and point tenderness over the affected bone.