sequestrum
{{Short description|Separated, dead bone piece during necrosis}}
{{More citations needed|date=January 2022}}
Image:Bony sequestrum in a child femur.jpg
A sequestrum (plural: sequestra) is a piece of dead bone{{cite book |title=Pathologic basis of veterinary disease |date=2017 |location=St. Louis, Missouri |isbn=978-0-323-35775-3 |pages=954–1008.e2 |edition=Sixth |url=https://www.sciencedirect.com/science/article/pii/B9780323357753000163 |access-date=30 August 2021 |language=en|last1=Zachary |first1=James F. }} that has become separated during the process of necrosis from normal or sound bone.
It is a complication (sequela) of osteomyelitis. The pathological process is as follows:
- infection in the bone leads to an increase in intramedullary pressure due to inflammatory exudates
- the periosteum becomes stripped from the ostium, leading to vascular thrombosis
- bone necrosis follows due to lack of blood supply
- sequestra are formed
The sequestra are surrounded by sclerotic bone which is relatively avascular (without a blood supply). Within the bone itself, the haversian canals become blocked with scar tissue, and the bone becomes surrounded by thickened periosteum.{{citation needed|date=August 2021}}
Due to the avascular nature of this bone, antibiotics which travel to sites of infection via the bloodstream poorly penetrate these tissues, hence the difficulty in treating chronic osteomyelitis.{{citation needed|date=August 2021}}
At the same time as this, new bone is forming (known as involucrum). Openings in this involucrum allow debris and exudates (including pus) to pass from the sequestrum via sinus tracts to the skin.{{citation needed|date=August 2021}}
Rarely, a sequestrum may turn out to be an osteoid osteoma, a rare tumor of the bone.