Osteomyelitis after a bite wound in cats: the bone sequestrum
4-year-old intact male cat with a bite abscess on the forearm 4 weeks ago, treated late and with only a few days of antibiotics. Lameness and a draining tract persist. Radiographs show irregular periosteal reaction on the radius, cortical lysis and a bone fragment more opaque than the adjacent bone, with sharp margins and surrounded by a radiolucent halo.
What does the fragment surrounded by the radiolucent halo represent?
chevron_right Show answer and explanation
A. A forming fracture callus
A callus is new bone bridging fragments and becomes progressively opaque; it does not appear as an isolated fragment surrounded by lucency.
B. A bone sequestrum: devitalised bone surrounded by granulation tissue
Correct. A sequestrum is necrotic bone, more opaque and sharply marginated, separated from living bone by granulation tissue (the halo). The new bone around it is called the involucrum. It perpetuates infection and must be removed.
C. A medullary bone infarct
Bone infarcts produce irregular medullary sclerosis, without a radiolucent halo or draining tract, and do not fit the bite wound history.
D. An osteosarcoma with mineralised matrix
It is a differential for any aggressive lesion, but the bite history, draining tract and sequestrum point to infection. If in doubt, submit samples for culture and histopathology.
lightbulb Key takeaway
Radiographic changes of osteomyelitis take about 10–14 days to appear after infection. While the sequestrum remains, antibiotics will not cure it: debride, remove the sequestrum and culture the bone (aerobes and anaerobes, common in cat bites).
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.