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A sequestrum is a piece of necrotic (dead) bone that has become separated from viable bone, typically due to chronic osteomyelitis.
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| Step | Description |
|---|---|
| Infection/inflammation | Pyogenic organisms invade the bone → vascular thrombosis |
| Ischemia | Bone segment loses its blood supply → necrosis |
| Sequestrum formation | Necrotic bone becomes isolated from healthy tissue |
| Involucrum | Surrounding new bone formation encapsulates the sequestrum |
| Cloaca | Drainage tract through involucrum (seen in chronic cases) |
| Condition | Relevance |
|---|---|
| Chronic osteomyelitis | Most common cause |
| Post-traumatic bone infection | After open fractures or orthopedic surgery |
| Tubercular osteomyelitis | May also produce sequestra |
| Diabetic foot infection | Small bony sequestra in metatarsals or tarsal bones |
| Modality | Imaging features |
|---|---|
| XR | X-ray can identify sequestrum only after weeks, once the necrotic fragment becomes mineralized. |
| • Sequestrum: Dense, sclerotic bone fragment within a lucent cavity | |
| • Involucrum: Thick, irregular periosteal new bone surrounding lesion | |
| • Cloaca: Linear tract from sequestrum to skin (sinus tract) | |
| • Lucent area: Surrounds sequestrum, representing pus/inflammatory tissue | |
| MR | Best for Detecting soft tissue abscesses, phlegmon, sinus tracts |
| • T1: Low signal intensity sequestrum, surrounded by inflammatory marrow | |
| • T2: Sequestrum is dark, surrounding hyperintense marrow edema | |
| • Post-contrast: Sequestrum shows no enhancement, but rim enhancement around it | |
| CT | Best modality for detecting sequestrum |
| • Dense bone fragment isolated within lucent cavity | |
| • Helps localize for surgical planning | |
| • Cloaca or sinus tract visualization |
| Entity | Differentiator |
|---|---|
| Bone island (enostosis) | Homogeneous dense focus with no surrounding lucency |
| Osteoid osteoma nidus | Central lucent area with sclerotic rim, intense pain |
| Bone infarct | Serpiginous inner margin, no sinus or cortical breach |
| Hardware fragment | History of surgery, artifact on CT |