This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bone and Imaging, Subject name: Orthopaedics
What is the earliest bony change of osteomyelitis on X-rays? 
Select and explain. 
A. Loss of soft tissue planes, B. Periosteal reaction, C. Sequestrum formation, D. Lytic defects
B: Periosteal reaction
Answer: B: Periosteal reaction 
Explanation: Pyogenic osteomyelitis on X-ray in 24-48 hours will show loss of soft tissue planes (earliest change on X-ray). Day 7 to 10-solid periosteal reaction (earliest bony change on X-ray).