Sequestrum Involucrum is made up of two words.
Sequestrum is a piece of dead bone that has been separated from normal bone in acute pyogenic osteomyelitis.
Involucrum is a new layer of bone tissue around the dead infected bone.
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This is a characteristics feature of Acute pyogenic osteomyelitis. The caustic agents are Salmonella, N Gonorrhea, Pasturella, S aureus, Mycobacterium tuberculosis etc.
Clinical features of such lesions are Bone pain with systemic sign of infection that are fever and leukocytosis. Lytic focus (abscess) surround by sclerosis of bone on x-ray. Lytic focus is called sequestrum and sclerosis is called involucrum. Diagnosis is made by cultural test.