A 7-year-old boy presents with a 6-week history of fever, pain in the left knee, and a draining sinus tract over the distal femur. Plain radiographs show cortical destruction, periosteal new bone formation, and a dense fragment of bone surrounded by lucency within the medullary cavity. The structure marked **C** in the diagram represents this dense devitalised bone fragment. Which of the following best describes the pathological significance of this finding in chronic osteomyelitis?
A. It indicates vascular compromise of the metaphyseal vessels and predicts poor long-term functional outcome
B. It is necrotic bone that acts as a nidus for persistent infection and must be surgically removed to achieve cure
C. It is a localized intraosseous abscess with a sclerotic margin that typically resolves with antibiotics alone
D. It represents new periosteal bone that encases the infection and indicates a favorable healing response
Explanation
Why option 1 is right
The structure marked C is the sequestrum — a fragment of devitalised (dead) bone that has been isolated from the blood supply by the inflammatory process. According to Apley's System of Orthopaedics, the sequestrum acts as a foreign body and a persistent nidus for bacterial growth, making it impossible for antibiotics alone to sterilize the bone. Surgical debridement and removal of the sequestrum is the essential management step in chronic osteomyelitis to achieve cure. The clinical presentation of a 6-week history with a draining sinus tract is classic for chronic osteomyelitis with sequestrum formation.
Why each distractor is wrong
Option 2: This describes the involucrum (structure B in the diagram), not the sequestrum. The involucrum is new periosteal bone that forms around the sequestrum and represents the body's attempt to wall off infection — it is a favorable sign, but the sequestrum itself remains a problem.
Option 3: This describes a Brodie's abscess, which is a localized subacute form of osteomyelitis with a sclerotic margin that may respond to antibiotics. A true sequestrum in chronic osteomyelitis requires surgical intervention, not antibiotic monotherapy.
Option 4: While metaphyseal vascular anatomy is important in acute haematogenous osteomyelitis pathogenesis (the sluggish loop allows bacterial seeding), the sequestrum itself is a consequence of necrosis, not a predictor of outcome — its removal determines prognosis.
High-YieldNEET PG
Sequestrum = dead bone = surgical debridement required; Involucrum = new bone = body's healing response.
Apley's System of Orthopaedics and Fractures, 10th ed
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