Topic: Acute osteomylitis, Ca Breast
Question: What is meant by involucrum. Describe the process of its formation.
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Involucrum is a layer of new bone that forms around an area of infected/necrotic bone in conditions like osteomyelitis.
Formation of involucrum:
– It starts with an infection of the bone, usually by bacteria like Staph aureus.
– This causes inflammation and death of a segment of bone (sequestrum).
– The infection stimulates the periosteum (outer lining of bone) to form new reactive bone around the infected site.
– This new bone is called involucrum and acts as a protective barrier to wall off the infected parts.
– The involucrum has holes (Cloaca) through which the pus and sequestrum can discharge to outside.
– So involucrum forms a shell around the infected bone and facilitates drainage, while keeping the infection localized.
– On radiographs, involucrum appears as a dense bony shell around sequestrum with cloaca draining the infections.
In summary, involucrum is formed by periosteal bone apposition around infected/necrotic bone in response to osteomyelitis. It walls off the infection and facilitates drainage via cloaca.
