Osteomyelitis

A 7-year-old boy from Mumbai presents with a 10-day history of fever (38.5°C), severe pain in the right knee, and refusal to bear weight. His mother reports he had a minor fall 2 weeks ago but did not sustain an obvious injury. On examination, the knee is swollen, warm, and tender; there is no obvious wound. Laboratory investigations show WBC 14,500/μL, CRP 8.2 mg/dL, and ESR 65 mm/h. Blood culture is negative. X-ray of the right knee shows soft tissue swelling but no bone lesion. MRI reveals a 3 cm × 2 cm area of T2 hyperintensity in the metaphyseal region of the distal femur with surrounding marrow edema and periosteal reaction. What is the most likely diagnosis?

Which organism is the most common causative agent of acute hematogenous osteomyelitis in children?

A 34-year-old male construction worker from Delhi presents with a 3-week history of progressive pain and swelling over the right tibia. He recalls a puncture wound to the sole of his foot 6 weeks ago while working barefoot on a construction site. On examination, the right foot shows a small, painless scar on the plantar surface; the tibia is warm, tender, and swollen. X-ray of the tibia shows a mixed lytic and sclerotic lesion in the diaphysis with periosteal reaction. Blood culture and bone culture both grow Pseudomonas aeruginosa. What is the most likely diagnosis and the primary reason for this organism's involvement?

Which clinical and radiological feature best distinguishes acute haematogenous osteomyelitis from chronic osteomyelitis?

In acute osteomyelitis, which vascular zone of the bone is most commonly affected by hematogenous spread?