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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2017/02/06 04:45:45」(JST)

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A sequestrum (plural: sequestra) is a piece of dead bone 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 osteum, leading to vascular thrombosis
bone necrosis follows due to lack of blood supply
sequestra are formed

An X-ray of a child's femur showing a bony sequestrum highlighted by the blue arrow.

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). Openings 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.

References

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1. 骨髄炎の病因 pathogenesis of osteomyelitis
2. 骨髄炎の疑いがある状況での画像検査法 approach to imaging modalities in the setting of suspected osteomyelitis
3. 成人における骨髄炎の概要 overview of osteomyelitis in adults
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Photodynamic therapy using Photofrin and excimer dye laser treatment for superficial oral squamous cell carcinomas with long-term follow up.

Toratani S1, Tani R2, Kanda T2, Koizumi K3, Yoshioka Y3, Okamoto T4.
Photodiagnosis and photodynamic therapy.Photodiagnosis Photodyn Ther.2015 Dec 30. pii: S1572-1000(15)30060-0. doi: 10.1016/j.pdpdt.2015.12.009. [Epub ahead of print]
OBJECTIVES: Photodynamic therapy (PDT) is a very effective treatment for superficial malignancies that does not result in loss of normal tissue. Here, we report successful PDT treatment of superficial oral cancers and its clinical outcome with long-term follow up.MATERIALS AND METHODS: Thirty-four s
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Application of platelet rich fibrin for management of an electrosurge induced osteonecrosis involving maxillary alveolus.

Suresh N1, Chandrasekaran B2, Muthusamy S3, Kannan S4, Muthu K5.
Singapore dental journal.Singapore Dent J.2015 Dec;36:39-43. doi: 10.1016/j.sdj.2014.11.004.
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Use of a porcine urinary bladder acellular matrix for corneal reconstruction in dogs and cats.

Balland O1, Poinsard AS1, Famose F2, Goulle F3, Isard PF4, Mathieson I5, Dulaurent T4.
Veterinary ophthalmology.Vet Ophthalmol.2015 Nov 12. doi: 10.1111/vop.12326. [Epub ahead of print]
OBJECTIVE: To describe the use of a porcine urinary bladder acellular matrix for surgical reconstruction of the cornea in cases of canine and feline deep corneal ulcers, and feline corneal sequestra.MATERIALS AND METHODS: Twenty-seven dogs and three cats with deep corneal ulcers and seven cats with
PMID 26559499