"Tendon and ligament injuries are very common in the horse--in performance horses and racehorses," said Tamara M. Swor, DVM, Dipl. ACVS, clinical instructor of equine surgery and emergency care at Washington State University, at the 50th annual American Association of Equine Practitioners (AAEP) Convention in Denver, Colo., Dec. 4-8, 2004. "When you look in the literature, the most commonly affected tendon is the superficial digital flexor tendon (SDFT)." However, Swor and her co-authors from Texas A&M University (TAMU) found out that deep digital flexor tendonitis (DDFT) is more common than previously thought, and it is found more often in the hind limb than the forelimb. Additionally, horses with hind limb DDFT are more likely to make a full recovery than horses with forelimb DDFT.

This information was found by performing a retrospective study of 15 years of DDFT cases at Texas A&M University in which ultrasound diagnosis was used. While magnetic resonance imaging (MRI) is quickly becoming a way to evaluate tendon lesions, most veterinarians use ultrasound evaluation of a possible DDFT injury because of unavailability of MRI. Swor and colleagues examined the radiographic and ultrasound examination findings in order to determine incidence and outcome.

"The DDFT was classified as abnormal if it had any changes in echogenicity (reflection of the emitted ultrasound signal), tendon fiber alignment, or an increase in tendon size," said Swor.

The mean age of the 78 horses was 9.7 years, and the mean duration of injury before presentation was 109 days. Among the 78 horses, there were 81 DDFT injuries. Fifty-four (69%) of the horses had an affected hind limb (28 in the left hind limb, 26 in the right hind limb), while 27 (35%) had DDFT lameness in the forelimb (19 in the right forelimb, eight in the left forelimb). When injuring a forelimb, 15 (55%) of the horses' DDFT lesions were in the pastern region. In most horses injuring a hind limb, the DDFT lesions were in the metatarsal (cannon bone) region (45 of the hind limb-affected horses, or 83%). 

Sixty-three (81%) of the cases were acute, in that the horses were found lame because of a traumatic injury to the limb. Chronic lameness was recorded in six (7%) of the horses, and nine (12%) had unknown injuries.

The lameness grade range in these horses was 1-4, using the AAEP lameness scale, with a mean of 2.5. Three of the horses had had palmar digital nerve neurectomies sometime prior to this injury.

Swor explained the prescribed rest and rehabilitation plans--the level of exercise was slowly increased, using ultrasound to guide decisions related to the horses' readiness to exercise. Recovery results were gathered by phone with the owner or the referring veterinarian--follow-up information was available for 54 horses at one month to 11 years after injury. Of these 54, 27 (50%) were considered to have successful outcomes, meaning they were sound and able to perform athletically.

Looking at those 27 horses, 21 (78%) were labeled as excellent. "Within this group, there were several that were barrel racers, involved in speed events, cutting, dressage, racing, jumping, eventing, and Western pleasure," said Swor. "The other six horses' recoveries were noted as good." Of the 27 horses, 17 had DDFT in a hindlimb and 10 had sustained a forelimb injury. Mean time from injury to competition in these horses was 9.3 months.

Re-injury in the DDFT was not as common as in horses with injured SDFT.

With only a few horses to analyze, Swor said it was difficult to judge whether using tendon splitting of the deep digital flexor tendon in some cases helped recovery.

"Our conclusions were that DDFT tendonitis is apparently more common in Western performance horses than we initially thought," she said, since the study was obviously weighted toward this discipline of horse. "It may be a function of what these horses do that make the horse predisposed. The injuries were found more frequently in the hind limbs, and mostly in the metatarsal region in the hind limb. It's possible that it's better for healing if it's in the hind limb."

She concluded that ultrasound is subjective and DDFT lesions do heal, but sometimes they do remain visible on ultrasound and might not look completely normal. As MRI becomes more available, it might be very useful for examining these types of cases.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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