Pediatrics · Year 3 · from Pediatrics

Case 1: Septic Arthritis of the Hip

Patient Demographics

  • Age: 3-year-old male
  • Sex: Male

Chief Complaint

"He won't walk and cries when we try to move his leg."

History of Present Illness

A 3-year-old boy is brought to the emergency department because he refuses to walk since this morning. Yesterday evening, his parents noticed he was limping and seemed fussy. Overnight, he developed fever to 39.5C. Today he will not bear weight on his right leg and cries out when anyone tries to move his hip. He has no history of trauma. He had an upper respiratory infection one week ago that resolved without treatment. He has been previously healthy with no prior hospitalizations.

Physical Examination

  • Vital Signs: Temperature 39.2C, HR 132 bpm, RR 24/min, BP 90/60 mmHg
  • General: Ill-appearing, irritable child lying with right hip flexed, abducted, and externally rotated
  • HEENT: Normal
  • Cardiovascular: Tachycardic, regular rhythm, no murmurs
  • Respiratory: Clear to auscultation
  • Abdomen: Soft, non-tender
  • Musculoskeletal: Right hip held in flexion, abduction, and external rotation; severe pain with any passive range of motion of right hip; minimal pain with knee or ankle examination; no erythema or warmth over hip (deep joint)
  • Neurologic: Unable to assess gait; moves all extremities when not touching right leg

Laboratory Findings

  • WBC: 18,500/uL with 82% neutrophils (elevated)
  • ESR: 65 mm/hr (elevated)
  • CRP: 8.5 mg/dL (elevated)
  • Blood culture: Pending
  • Hip ultrasound: Right hip effusion present
  • Hip arthrocentesis: Turbid yellow fluid; WBC 85,000/uL with 92% neutrophils; Gram stain shows gram-positive cocci in clusters

Diagnosis

Septic arthritis of the right hip (Staphylococcus aureus)

Clinical Reasoning

This child meets all four Kocher criteria for septic arthritis: fever >38.5C, non-weight-bearing, ESR >40 mm/hr, and WBC >12,000/uL. With all four criteria positive, the probability of septic arthritis exceeds 99%. The hip is held in the position of maximum capsular volume (flexion, abduction, external rotation) to minimize intra-articular pressure. Hip ultrasound confirms effusion, and arthrocentesis reveals purulent fluid with high WBC count and gram-positive cocci. The hip joint is a surgical emergency because increased intra-articular pressure can compromise blood supply to the femoral head, leading to avascular necrosis.

Management

  1. Emergent surgical drainage: Open arthrotomy or arthroscopic drainage of the hip joint (hip requires operative drainage unlike some other joints)
  2. Intravenous antibiotics: Nafcillin or cefazolin for MSSA; add vancomycin if MRSA suspected or in high-prevalence areas
  3. Blood and synovial fluid cultures: Guide antibiotic adjustment once sensitivities available
  4. IV antibiotics duration: Minimum 3-4 weeks total; transition to oral when clinically improved and CRP trending down
  5. Monitoring: Serial CRP to monitor treatment response (should decline within 3-5 days)
  6. Physical therapy: Early mobilization once acute infection controlled

Clinical Image

Image Description: A child with septic arthritis of the hip demonstrating the characteristic position of comfort with the hip flexed, abducted, and externally rotated to maximize joint capsule volume and minimize intra-articular pressure.

Source: Radiopaedia URL: https://radiopaedia.org/cases/septic-arthritis-hip-paediatric License: CC BY-NC-SA 3.0

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