Moderate to severe superficial digital flexor (SDF) tendon lesions in Thoroughbred racehorses have typically carried a poor prognosis for a return to racing and a lengthy rehabilitation process for horses that do return. But a team of veterinarians recently took a closer look at a procedure that could help improve the outcome for Thoroughbreds with such injuries: superior check ligament desmotomy surgery. The surgery—which involves cutting the accessory (superior check) ligament of the SDF tendon—is based on the premise that the ligament, once healed, is slightly longer than it was pre-cutting, resulting in a partial transfer of strain off the SDF tendon and onto other limb structures, particularly the suspensory ligament. “It gives the horse a little more tendon to work with,” explained study author and surgeon Larry Bramlage, DVM, MS, Dipl. ACVS, of Rood & Riddle Equine Hospital, in Lexington, Kentucky. “In addition, it takes the tension off the tendon during the healing period, reducing fibrosis (scarring) during healing.” Bramlage and Alaine Hu, DVM, presently of Kirkwood Animal Hospital in Campbell, California, looked at 332 Thoroughbred racehorses that underwent the surgical procedure at Rood & Riddle. Using the horses’ race records to assess outcome, the team sought to determine how many of the treated horses returned to racing, how long it took them to return, and how many race starts they made post-surgery. “If you use the race records and look at whether a horse raced, or did not race, it’s clear cut,” he explained. “There’s no subjective judgment, and the results are collected by a third party.” If future studies were to utilize a similar design, he added, researchers could compare different treatments across the same injury. All of the horses in the study had Grade 2, 3, or 4 tendon lesions, “which are holes in the tendon,” noted Bramlage. “They were not Grade 1 lesions, which just have edema (swelling).” Researchers know that this latter, milder form of tendon injury generally responds well to nonsurgical treatment and, therefore, affected horses were not recommended for surgery. Of the 332 horses in the study, 228 (69%) went on to race post-surgery. The team also considered career longevity post-surgery. Of the 228 horses that returned to racing, 159 (70%) raced five or more times after surgery (representing 48% of all horses that underwent the surgery). With respect to the length of time between the surgery and a return to racing, the researchers found that, on average, horses returned to training about four months postoperatively (and following ultrasonographic evaluation) and began racing 10 to 11 months after surgery. This is a much shorter timeframe than previously recommended in the literature, which suggested horses be totally off work for 10 to 12 months, said Bramlage. The study results also revealed that age had an impact on post-surgery race performance: “Of the horses that were 5 years old at the time they were injured—which means they would be coming back at 6 or 7—only 44% of them raced (after surgery), which was much less than the 2 to 4 year olds,” said Bramlage. He also noted that because riding horses in other disciplines are typically older and, based on his experience, suffer from tendon injuries of a different nature than racehorses, the findings of this study should not be extrapolated to the treatment of those horses. The study, “Racing performance of Thoroughbreds with superficial digital flexor tendonitis treated with desmotomy of the accessory ligament of the superficial digital flexor tendon: 332 cases (1989-2003),” was published in the Journal of the American Veterinary Medical Association.
