Sonographic Diagnosis of Exostoses of the Caudal Distal Radius

Exostoses of the caudal perimeter of the distal radius resulting in lameness accompanied by intermittent effusion of the carpal synovial sheath have been described. Such exostoses are categorized as either solitary osteochondromas, which are typically located 2–4 cm proximal to the physeal scar, or physeal remnant spikes, which originate directly over the physeal scar. Osteochondromas typically affect young horses, whereas physeal remnant spikes may affect older horses as well. Radiography has been routinely used for the detection of these exostoses. Radiographic recognition of small physeal remnant spikes can be more difficult because of superimposition over the physeal scar, and some osteochondromas are small and difficult to detect. However, not all exostoses are clinically important. Arthroscopic removal of clinically important exostoses is the treatment of choice. The procedure can also be used to examine the carpal sheath in which an exostosis is not radiographically apparent but lameness has been isolated to the carpal synovial sheath. Sonographic detection of distal radial bone spikes and osteochondromas has been mentioned in the literature, but the procedure and sonographic features were not described in detail. Ultrasonography can be used to diagnose exostoses that are not radiographically apparent as well as aid in determining their significance by imaging their extension into the carpal sheath and/or associated structures. The purposes of this paper are to describe the sonographic appearance and location of clinically important caudal radial exostoses, highlight the importance of using ultrasonography to identify exostoses that are not evident radiographically, and increase awareness of caudal distal radial exostoses as a potential cause of lameness in the absence of carpal sheath effusion.