Sequestra

A sequestrum is a piece of dead bone that has become separated from normal/sound bone during the process of necrosis . It is a complication (sequelae) of osteomyelitis.

Pathological process of development of sequestra:

• infection in the bone -> inflammatory exudate -> increase in intramedullary pressure
• periosteum becomes stripped from the osteum -> vascular thrombosis
• lack of blood supply -> bone necrosis
• sequestra are formed

Due to the avascular nature of sequestra, antibiotics which travel to sites of infection via the bloodstream, poorly penetrate these tissues. Hence the difficulty in treating chronic osteomyelitis.

At the same time as sequestra are developing, new bone is forming (known as involcrum). Openings in the involcrum allow debris and exudates (including pus) to pass from the sequestrum via sinus tracts to the skin.

References:

• http://en.wikipedia.org/wiki/Sequestrum

• Image from http://www.steinergraphics.com/surgical/006_19.3.html