A 6-year-old boy presents with high fever, severe pain over the distal femur, and refusal to move the knee for 3 days. ESR is 80 mm/hr, CRP is elevated, and X-ray shows only soft tissue swelling. The most likely causative organism is:
- A Streptococcus pyogenes
- B Haemophilus influenzae
- C Staphylococcus aureus ✓
- D Pseudomonas aeruginosa
Correct answer: C. Staphylococcus aureus
Explanation
Staphylococcus aureus is the causative organism in over 80% of cases of acute haematogenous osteomyelitis across all age groups. In children, the metaphysis of long bones — especially the distal femur and proximal tibia — is the most common site because of sluggish blood flow in the sinusoidal vascular loops. Early X-rays are normal because periosteal new bone and lytic changes appear only after 10–14 days. Blood cultures and MRI (most sensitive early) confirm the diagnosis.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.