Lameness in cutting horses is a major cause of loss of use and can lead to career-limiting injuries. Most cutting horses are treated for hind limb lameness as opposed to forelimb lameness.1 Tendonitis of the SDF in the forelimbs is rarely reported as a cause of lameness in cutting horses, and to our knowledge, there are no reports on the development of SDF tendonitis in this particular class of equine athletes.
In racehorses, tendonitis of the SDF tendon in the forelimb is among the most common musculoskeletal injuries2 and has been reported to account for 6% to 13% of racing-related injuries.3 Most of the published data regarding SDF tendonitis in horses are associated with sport and racing disciplines,4 with the lesion most commonly located in the center of the tendon within the mid-metacarpal region5,6 (generating a classic core lesion appearance in ultrasonographic images). It has been postulated that core lesions account for most of the tendon injuries in racehorses because of the repeated high-strain cycling in the center of the tendon, which results in microtrauma.7 Tendonitis of the SDF in horses other than cutting horses is commonly considered to have a poor prognosis with a high recurrence rate and is often a career-ending injury.4,8–11
After tendon injury, the chances of affected racehorses returning to racing are < 50%, and of those that do return to racing, nearly half will reinjure the tendon.12 Clinical signs of SDF tendonitis in racehorses include acute swelling on the palmar aspect of the metacarpus (resulting in a bowed tendon appearance), mild to severe lameness, and detectable heat and signs of pain on palpation of the limb. Diagnosis of tendon lesions is commonly based on history, clinical findings, and results of an ultrasonographic examination. In ultrasonographic images, the affected region of the tendon appears enlarged and hypoechogenic with decreased linear fiber pattern and changes in shape, margin, or position of the tendon, compared with the unaffected regions of the tendon.
Tendon failure occurs as a single overstrain incident or cumulative fatigue failure as a result of cyclic loading.9,13 Exercise-induced degenerative change within the SDF tendon has been proposed as a possible mechanism of injury in racehorses and sport horses,2 and results of a study8 suggest that with increasing age, the risk of SDF tendon injury increases. There are also reports10,11 that SDF tendons may be at increased risk for injury with fatigue of the deep digital flexor muscle. The purpose of the study reported here was to characterize SDF tendon lesions in cutting horses and determine the recurrence rate and prognosis for this condition. Additionally, we obtained information regarding treatment and rehabilitation protocols commonly used to treat these injuries in a clinical setting.
Superficial digital flexor
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