Sequestrum
Encyclopedia
A sequestrum is a piece of dead bone
that has become separated during the process of necrosis
from normal/sound bone.
It is a complication (sequela) of osteomyelitis
. The pathological process is as follows:
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.
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.
At the same time as this, new bone is forming (known as involucrum
). Opening in this involucrum allow debris and exudates (including pus) to pass from the sequestrum via sinus tracts to the skin.
Rarely, a sequestrum may turn out to be an osteoid osteoma, a rare tumor of the bone.
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
that has become separated during the process of necrosis
Necrosis
Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...
from normal/sound bone.
It is a complication (sequela) of osteomyelitis
Osteomyelitis
Osteomyelitis simply means an infection of the bone or bone marrow...
. The pathological process is as follows:
- infection in the bone leads to an increase in intramedullary pressure due to inflammatory exudates
- the periosteumPeriosteumPeriosteum is a membrane that lines the outer surface of all bones, except at the joints of long bones. Endosteum lines the inner surface of all bones....
becomes stripped from the osteum, 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
Haversian canals
Haversian canals are a series of tubes around narrow channels formed by lamellae. This is the region of bone called compact bone. Osteons are arranged in parallel to the long axis of the bone...
become blocked with scar tissue, and the bone becomes surrounded by thickened periosteum.
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.
At the same time as this, new bone is forming (known as involucrum
Involucrum
Involucrum is a layer of new bone growth outside existing bone seen in pyogenic osteomyelitis. It results from the stripping off of the periosteum by the accumulation of pus within the bone, and new bone growing from the periosteum....
). Opening in this involucrum allow debris and exudates (including pus) to pass from the sequestrum via sinus tracts to the skin.
Rarely, a sequestrum may turn out to be an osteoid osteoma, a rare tumor of the bone.