A 45-year-old man with a 10-year history of recurrent drainage from an old tibial fracture site presents with purulent discharge from a sinus tract. Plain radiographs show a dense, sclerotic bone fragment surrounded by a shell of new bone with a central opening. The structure marked **A** in the diagram represents the dense necrotic bone fragment. Which of the following best explains why this structure appears radiographically denser (whiter) than the surrounding bone?

Question

Accepted Answer

B. The sequestrum is avascular necrotic bone that appears dense because surrounding viable bone undergoes disuse osteoporosis, creating a relative radiographic contrast. ## Why option 1 is right

The sequestrum appears radiographically dense (sclerotic/white) not because it is inherently more mineralized, but because the surrounding viable bone undergoes disuse osteoporosis as a reaction to chronic infection and immobility. The sequestrum itself is dead, avascular bone that has lost its blood supply and cannot remodel; it remains relatively unchanged in mineral content. The surrounding live bone becomes osteoporotic (darker/lucent), making the dead sequestrum appear relatively whiter by contrast. This radiographic appearance is a classic teaching point in chronic osteomyelitis and is fundamental to recognizing the sequestrum on plain films (Campbell's Operative Orthopaedics 14e; IDSA Osteomyelitis Guidelines).

## Why each distractor is wrong

- **Option 0**: The sequestrum is dead, avascular bone — osteocytes within it are non-viable and cannot undergo hyperplasia. Living bone would appear darker due to vascularity and remodeling activity.
- **Option 2**: The sequestrum is avascular by definition; it cannot have increased vascularity or osteoblastic activity. Increased osteoblastic activity occurs in the surrounding involucrum (new reactive bone), not in the dead sequestrum.
- **Option 3**: The sequestrum IS actual necrotic bone, not calcified granulation tissue. It is a fragment of the original cortex or medullary bone that has lost its blood supply and become isolated.

**High-Yield:** Sequestrum appears dense because surrounding bone is osteoporotic, not because the sequestrum itself is hypermineralized — it is dead bone in contrast to living bone.

[cite: Campbell's Operative Orthopaedics 14e; IDSA Osteomyelitis Guidelines]

Answer

A. The sequestrum is composed of living osteocytes that have undergone hyperplasia in response to chronic infection

Answer

C. The sequestrum represents areas of pathologic calcification within granulation tissue, not actual bone

Answer

D. The sequestrum has increased vascularity and osteoblastic activity, causing increased mineral deposition compared to normal bone

Explanation

Why option 1 is right

Why each distractor is wrong

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