Ultrasonographic appearance of bony abnormalities at the dorsal aspect of the fetlock joint in geriatric cadaver horses

This article describes the ultrasonographic (US) appearance of bony abnormalities on the dorsal aspect of the third metacarpal/metatarsal bone of the equine fetlock in cadavers with radiographic signs of osteoarthrosis. After US, computed tomography was undertaken to better characterise the lesions. Twelve fetlock joints were collected and all had more than one bone abnormality on US. Normal subchondral bone appeared on US as a well-defined and regular hyperechoic line with distal acoustic shadowing. Bone abnormalities detected on US included (1) gaps in the proximal subchondral bone filled with material of heterogeneous echogenicity, (2) bone fragments represented as small straight smoothly delineated hyperechoic lines with distal shadowing located superficial to the surface of the adjacent bone, (3) proximal new bone formation visible as mild to severe cortical protrusions, (4) marginal osteophytoses seen as an elevation of the hyperechoic surface of the subchondral bone at the edges of the joint surfaces, (5) indentations in subchondral bone seen as a concave deviation of the hyperechoic line without interruption, (6) focal or diffuse irregularities of the subchondral bone seen as disruptions of the normal smooth bony contours, and (7) focal hyperechoic spikes originating from the subchondral plate and invading the articular cartilage. These findings are discussed.