Ultrasonographic findings in two calves with bone sequestration of an extremity

ACCORDING to the pathological definition, a bony sequestrum is a piece of dead bone that has become separated from the living bone during the process of necrosis. In horses and cattle, most bony sequestra are associated with localised trauma and generally involve the distal extremities because of their minimal soft-tissue coverage (Clem and others 1987, Firth 1987, Valentino and others 2000, Milner 2008). Bone sequestration can also develop following haematogenous bone infection resulting in bone necrosis (chronic osteomyelitis; Firth 1987, Lew and Waldvogel 2004) and open fractures that have a piece of broken-off bone left in the wound (Hedrickson 2005, Braun and others 2009). The diagnosis is confirmed by radiography, which typically reveals calcified tissue within the lucent lesion surrounded by sclerotic bone (Sayegh and others 2001, Reef and others 2004). At the same time, an involucrum that is formed in layers of exudates, lytic bone and capsule (periosteal new bone and sclerosis of the adjacent cortex) around the sequestrum can be identified (Clem and others 1987, Desrochers and others 2001, Pineda and others 2009). Although ultrasound waves are almost completely reflected and highly attenuated by normal cortical bone (Reef and others 2004, Pineda and others 2009), they allow the exploration of what lies within lytic bone, once the dense cortical bone has been partially destroyed, because lytic and periosteal new bone are less dense than sound cortical bone and transmit ultrasound waves. In fact, ultrasonographic examination has been used in cattle for detecting the bone sequestrum of a fractured sternebra (Braun and others 2009) and a rib that was inaccessible to radiography (Valentino and others 2000), but the ultrasonographic features have not been characterised. Even though ultrasound is widely used to diagnose bone sequestra, the few studies on the ultrasonography of bone sequestration in large animals …