Sequestrum

{{Short description|Separated, dead bone piece during necrosis}} {{one source|date=October 2025}} thumb|right|X-ray of a child's femur, showing a bony sequestrum indicated by the blue arrow. A '''sequestrum''' (plural: sequestra) is a piece of dead bone<ref>{{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. |url-access=limited}}</ref> that has become separated during 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 * lack of blood supply causes bone necrosis * sequestra are formed

The sequestra are surrounded by sclerotic bone, which is relatively avascular (without a blood supply). So, 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}}

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}} Meantime, new bone (involucrum) forms. 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 type of bone tumor.

==References== {{Reflist}} {{Osteochondropathy}}

Category:Bone fractures Category:Gross pathology