A 6-year-old boy presents with fever, acute painful swelling, and inability to move his right knee for 3 days. Joint aspiration yields 80,000 WBCs/µL with 94% PMNs, glucose <40 mg/dL, and culture grows Staphylococcus aureus. The most critical early complication if treatment is delayed is:

• A Avascular necrosis of the epiphysis due to tamponade of the epiphyseal blood supply by intra-articular pressure ✓
• B Reactive arthritis (Reiter's syndrome)
• C Osteosarcoma arising from the joint infection
• D Septicaemia from bacteraemia alone

Explanation

In septic arthritis of large joints, elevated intra-articular pressure from purulent effusion (often >60 mmHg) can tamponade the epiphyseal blood vessels that traverse the synovium and capsule in children, causing AVN of the epiphysis (e.g., femoral head in hip septic arthritis). Proteolytic enzymes in pus also destroy articular cartilage within 6–8 hours. Emergency arthrotomy (open drainage), not arthroscopic washout alone, is required for hip septic arthritis because of the constrained anatomy. Intravenous antistaphylococcal antibiotics accompany drainage.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.