This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Skeletal infections, Subject name: Orthopaedics
Radiologically, earliest sign of osteomyelitis is - 
Select and explain. 
A. Loss of muscle and fat planes, B. Periosteal reaction, C. Callus formation, D. Presence of sequestrum
B: Periosteal reaction
Answer: B: Periosteal reaction 
Explanation: Osteomyelitis is the infection of bone by microorganisms.It can be acute or chronic. Acute osteomyelitis: This can be primary (haematogenous)or secondary(following open fracture or bone opeaion). Staphylococcus aureus is the commonest causative organism. C/f: Child presents with an acute onset of pain and swelling at end of a bone,associated with systemic features of infection like fever. Investigations: Blood- polymorphonuclear leucocytosis and an elevated ESR. X-rays - The earliest sign to appear in X ray is a periosteal new bone deposition at metaphysis.This is called periosteal reaction.It takes about 7-10 days to appear. Bone scan- bone scan using Tc 99 may show increased uptake by bone in the metaphysis. REF:Essential Ohopaedics.Maheswari &Mhaskar.Edition 9.Pg no:169