This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infection of Bones & Joints, Subject name: Orthopaedics
All dead or devitalized bone must be identified by the preoperative injection of sulphan blue which stains all living tissue green, leaving dead material unstrained in 
Select and explain. 
A. Acute osteomyelitis with sequestrum, B. Subacute haematogenous osteomyelitis with sequestrum, C. Chronic osteomyelitis with cavity, D. Chronic osteomyelitis with sequestrum
D: Chronic osteomyelitis with sequestrum
Answer: D: Chronic osteomyelitis with sequestrum 
Explanation: (Chronic osteomyelitis with sequestrum) (38-A)Chronic osteomyelitis - under antibiotic cover all infected soft tissue and all dead or devitalized bone must be excised, dead material can be identified by the preoperative injection of sulphan blue which stains all living tissues green, leaving dead material unstained;* Sequestra (pieces of dead bone), act as substrates for bacterial adhesion in much the same way as foreign implants, ensuring the peristance of infection until they are removed or discharged through draining sinuses.Subacute haemotogenous osteomyelitis Distal femur and the proximal and distal tibia are the favourite sites* Sometimes the cavity is surrounded by a halo of selerosis (classic Brodie's abscess)