Distal Radial Exostosis and Osteochondroma of the Distal Radius in Horses
Exostosis of the caudal aspect of the distal radial physis can cause tenosynovitis of the carpal sheath and damage to the deep digital flexor tendon. Exostosis is differentiated from an osteochondroma based on its location and histologic appearance. Osteochondromas are present on the caudal aspect of the distal radius metaphysis normally 2–4 cm proximal to the distal radial physis. Osteochondromas also have hyaline cartilage remnants present on histologic examination (exostosis do not have hyaline cartilage). Irrespective of origin, these two conditions can cause lameness (swinging leg) and carpal sheath tenosynovitis.
Diagnosis is generally made by radiography, but ultrasonic examination may be helpful to define the presence of soft-tissue injury. The condition can be treated successfully via tenoscopy of the carpal sheath with removal of the protruding mass and identification and debridement of any concomitant damage to the deep flexor tendon. The prognosis is good and depends on the degree of soft-tissue damage.