Vet Forum: The Expert View
By Stuart Williamson BVSC MRCVS
Carpal sheath issues in focus National Hunt horses are more at risk of sustaining accessory carpal bone fractures
T
he carpal sheath is a synovial structure on the back of the foreleg that extends from the lower forearm region to the mid-cannon. This sheath wraps around the superficial digital flexor tendon (SDFT) and the deep digital flexor tendon (DDFT) as they run over the back aspect of the knee. Synovial fluid produced by the sheath lubricates the tendons and therefore reduces friction. In the normal horse, the carpal sheath contains only a small amount of synovial fluid and therefore cannot be palpated. Carpal sheath issues can range from mild inflammation (tenosynovitis) and distension of the carpal sheath, without lameness, to non-weight-bearing lameness associated with significant damage to one or more of the soft tissue or bony structures enclosed within the sheath. We will take a look at some of these issues, in addition to how they may be diagnosed and some of the management options available.
DISTAL RADIAL OSTEOCHONDROMA
An osteochondroma is an overgrowth of bone with a cartilage cap that occurs
near the growth plate at the end of a long bone. In the horse, they are most frequently identified above the level of the growth plate at the back of the radius in the lower forearm. Osteochondromata can cause damage to the muscular portion of the DDFT as it runs over this abnormal bony protuberance. This can result in inflammation and haemorrhage within the carpal sheath and lameness of varying severity. Some ostechondromata can however remain asymptomatic. The diagnosis of an osteochondroma is made by radiography. Ultrasound examination can then aid in evaluating the soft tissue structures within the carpal sheath that may be damaged by the osteochondroma, in addition to evaluating the character of any carpal sheath fluid. Keyhole (tenoscopic) surgery under general anaesthesia may be required to remove the osteochondroma in addition to evaluating the remainder of the carpal sheath to identify any concurrent injury. If this condition is addressed promptly, and there is no concurrent significant DDFT damage, the prognosis for a return to full athletic function is
››
Figure 1 A comminuted accessory carpal bone fracture (red arrow). This was a career-ending injury
THE OWNER BREEDER 93
