Suspensory Injury's Effect on Future Racing Performance

You had high hopes for your Thoroughbred racing prospect until he sustained a suspensory ligament branch injury as a yearling. The question now is, after rehab, should you continue to pursue his racing career, or should you skip the track and point him down a different career path? Recent study results suggest the answer depends on the severity of the injury.

Jonathan McLellan, BVMS, MRCVS, and Sarah Plevin, BVMS, MRCVS, of Florida Equine Veterinary Associates, in Ocala, recently hypothesized that youngsters who injure a suspensory ligament branch are less likely to race to their potential. McLellan presented the results of their retrospective study on the topic during the 2013 American Association of Equine Practitioners' Convention, held Dec. 7-11 in Nashville, Tenn.

Specifically, McLellan reviewed juvenile insertional suspensory branch injuries (JISBI), which occur at the suspensory ligament's insertion on the proximal sesamoid bones (the two small bones sitting at the base of the cannon bone in back of the fetlock joint) between ages 1 and 2. Clinical signs include localized heat and swelling, pain on palpation, variable lameness (typically following speed work), a dropped appearance of the fetlock, and fetlock joint effusion (swelling). Veterinarians typically diagnose JISBI using ultrasound.

McLellan said the aim of their research was to allow veterinarians to provide evidence-based advice on the disease to owners of horses with this injury.

In the study, McLellan reviewed medical records from 85 juvenile horses that presented to his clinic over a three-year period with JISBI in one suspensory ligament branch. For controls, he matched each case with its disease-free maternal sibling and compared the number of race starts, earnings, speed figures, and age at first start between cases and controls.

McLellan found that:

  • Of the injured horses, 56 eventually raced (23 as 2-year-olds and 53 as 3-year-olds), indicating they were four times less likely to start in a race than control horses;
  • Sixty-six percent of JISBI cases started a race compared with 89% of matched controls;
  • Total earnings per start for JISBI cases were less than matched controls;
  • Mild JISBI cases performed similarly to matched controls by 3 years of age;
  • Horses with moderate to severe JISBI performed worse than controls; and 
  • Reinjury rate increased with initial injury severity, with 37% of the most severe JISBI cases suffering a reinjury by the end of their 3-year-old racing season, compared with 10% of mild cases and 23% of moderate cases.

Overall, McLellan said horses with JISBI have decreased starts and earnings compared to controls.

However, "although JISBI results in a reduced likelihood of starting a race, those horses that make it to race show very few differences in earnings from controls and might live up to their genetic potential."

In conclusion, McLellan said veterinarians should take radiographs and ultrasound images if they suspect a suspensory branch injury, and they should always consider the injury's severity when providing a prognosis for owners.


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