Musculoskeletal ImagingCallus
a meshwork of woven bone that develops during
fracture repair and normally later becomes replaced by adult bone. After a
fracture, a
haematoma forms between the
fracture ends,
clotting takes place and an acute inflammatory response follows. Fibrovascular tissue, which replaces the
clot, lays down collagen that becomes mineralized to form the provisional callus. The new bone rapidly envelops the ends of the bones and helps produce stability at the
fracture site.
Exuberant callus formation may follow certain fractures (e.g. clavicular fractures) and be associated with neurovascular defects.
Tumoural callus is also seen in osteogenesis imperfecta (Fig.1) and may mimic an osteosarcoma.
Excessive endosteal callus formation surrounding fracture sites may be a feature of Cushings disease; it may also be seen after administration of steroid medications.
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Lateral radiograph of the femur in a patient with osteogenesis imperfecta demonstrates a large ossific density about the femoral diaphysis owing to a healing fracture. Since no fracture line is visible, this appearance potentially mimics osteosarcoma.
(Courtesy of Brian Howard, MD, Charlotte, NC)
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Callus, Fig.1 | |