Slabs

Slab fractures extend from one articular surface to another in a proximal to distal direction. The third carpal bone is affected most frequently,39,56,59,60 although fractures of the fourth, radial, and intermediate carpal bones have been reported.61 Racehorses are the most likely to be affected.

Dorsal plane slab fractures are the most likely to occur, particularly affecting the medial facet of the third carpal bone.39-42,46 They may range in depth from 8 to 25 mm and may be displaced or nondisplaced (Fig. 23.21). Lameness varies in severity from mild to severe. With complete displaced fractures, significant effusion, soft tissue swelling, and severe lameness are usually present, but horses with a nondisplaced incomplete fracture may have no localizing clinical signs. Prognosis for racing following incomplete nondisplaced fracture of the medial facet of the third carpal bone appears to be good following lag screw fixation.62,63

A complete series of radiographs should be obtained, including dorsoproximal/dorsodistal views. Fractures of the radial facet of the third carpal bone are best visualized on lateromedial, flexed lateromedial, and dorsolateral/palmaromedial oblique views and a dorsoproximal/dorsodistal view of the distal row of carpal bones.61 In some horses, a fracture can be seen only in the dorsoproximal/dorsodistal projection, especially if the fracture is nondisplaced (Fig. 23.22). Concurrent damage to the dorsal distal aspect of the radial carpal bone is a frequent occurrence, as is concurrent third carpal bone sclerosis. Complete radiographic evaluation of the contralateral limb should also be performed, because lesions may occur bilaterally.

Sagittal plane fractures occur less commonly than dorsal plane fractures and may be incomplete.64-66 They primarily affect the medial facet of the third carpal bone (see Fig. 23.22). As with other osteochondral fractures, horses are quite lame at the time of fracture, and the contralateral limb may be involved. Racehorses with sagittal slab fractures of the third carpal bone can have a favorable prognosis for return to racing, particularly if treated surgically.67 Fracture of other carpal bones has been reported but is relatively rare.

Sagittal fractures of the third carpal bone are best seen on dorsoproximal/dorsodistal and dorsomedial/palmarolateral oblique views. The lucent fracture line is often located parallel to the articulation between the second and third carpal bones. Radiographs of the entire carpus should be assessed for concurrent osteochondral injury.