Equine Lameness and Surgery Advances Discussed at AAEP

What was the hottest news in equine veterinary medicine in 2009? During the popular Kester News Hour session at the annual American Association of Equine Practitioners (AAEP) convention, three top veterinarians (who focus on equine reproduction, internal medicine, and lameness/surgery) summarized the top news topics and the most significant research reports of the year for a record crowd of equine veterinarians.

The Kester presenters during the 2009 AAEP convention, held Dec. 5-9 in Las Vegas, Nev., included:

  • Scott E. Palmer, VMD, Dipl. ABVP (Equine Practice), hospital director and a staff surgeon of the New Jersey Equine Clinic in Clarksburg, N.J., past president of the AAEP and American Board of Veterinary Practitioners.
  • Margo L. Macpherson, DVM, MS, Dipl. ACT, associate professor and section chief in reproduction at the University of Florida, and past president of the American College of Theriogenologists.
  • Bonnie R. Rush, DVM, MS, Dipl. ACVIM, professor of equine internal medicine at Kansas State University, winner of the 1996 and 2003 Carl J. Norden Distinguished Teacher Award, the 2002 Pfizer Award for Research Excellence, and the 2004 Outstanding Woman Veterinarian of the Year.

Shock wave therapy for wounds Although extracorporeal shock wave therapy (ESWT) is generally used to treat orthopedic problems, Palmer discussed one study published in the Journal of the American Veterinary Medical Association (JAVMA) that found weekly shock wave therapy shortened the healing time of experimentally created wounds of the lower limb (from 90 days to 76 days). There was no significant difference in the quality of healing between ESWT-treated limbs and controls, and the mechanism for the shortened healing time is unclear.

Reference:

Morgan, D.D.; McClure, S.; Yeager, M.J.; Schumacher, J.; Evand, R.B. Effects of extracorporeal shock wave therapy on wounds of the distal portion of the limbs in horses. Journal of the American Veterinary Medical Association 2009;234:1154-61.

Racing speeds--have they topped out? A study published in the Journal of Experimental Biology suggests that a plateau has been reached in the performance of racing Thoroughbreds, said Palmer. "Racing speeds have not increased significantly in Thoroughbred racing in the last 40-60 years," he commented. "This study says the predictive maximum racing speed of Thoroughbreds is only about 0.5-1% faster than current racing records in Triple Crown races. This study concluded that there is a natural upper speed limit, and Thoroughbreds have been running pretty close to it for the last few decades."

Reference:

Denny, M.W. Limits to running speed in dogs, horses and humans. The Journal of Experimental Biology 2008; 211:3836-3849.

Early exercise and joint problems Some researchers have shown exercising foals early in life is good for soundness and others have found it is harmful. Researchers on this study, published in Equine Veterinary Journal (EVJ), stated there currently is no clear consensus as to whether young horses benefit from or are harmed by exercise regimes that are more rigorous than free movement and play. However, the authors did find an apparent association with animal size and the severity of joint damage due to exercise. There are physical limitations to the ability of the supporting limbs of horses to increase in size proportional to increases in the upper body mass. In that way, anatomical properties of the horse define, to some degree, the prevalence and severity of joint injury.

"Well-controlled prospective studies in horses are still needed to determine optimum training," Palmer commented. "Since the horse appears to be a good experimental model for humans, the results of those studies will have important implications for research into the effect of early athletic training upon children."

Reference:

Adams, M.A.; Silver, I.A. Early enhanced exercise: Damaging or beneficial to joints? Equine Veterinary Journal 2009;41:515-516.

Hock osteoarthritis--diagnosis and prognosis Palmer noted, "Although many sound horses have radiographic changes of the hock consistent with osteoarthritis of the small tarsal joints, a diagnosis of 'bone spavin' is often made on the basis of radiographic evaluation alone." Researchers on a study published in Equine Veterinary Journal found there is no relationship between severity of clinical presentation, duration of lameness, response to diagnostic anesthesia (nerve blocks), and clinical outcome between mild or severe osteoarthritis in the small tarsal (lower hock) joints. However, horses with milder joint pathology (as seen on radiographs) tend to do better following treatment.

The authors of this study concluded that although the response to intra-articular anesthesia remains the gold standard for diagnosis of small tarsal joint osteoarthritis, it remains difficult to predict which horses are likely to improve following treatment, said Palmer.

Reference:

Byam-Cook, K.L.; Singer, E.R. Is there a relationship between clinical presentation, diagnostic and radiographic findings and outcome in horses with osteoarthritis of the small tarsal joints? Equine Veterinary Journal 2009;41:118-123.

Joint medications Experimentally induced joint inflammation was treated with mepivacaine hydrochloride, triamcinolone acetonide, or both in a study published in the American Journal of Veterinary Research (AJVR). Researchers found mepivacaine eliminated lameness quickly and did not compromise the effect of triamcinolone acetonide, which acted as a potent anti-inflammatory agent.

Another AJVR study found that when using a carpal chip model to induce arthritis, neither polysulfated glycosaminoglycan (PSGAG) or hyaluronic acid (HA) improved clinical signs (lameness). However, both had disease-modifying effects, meaning they improved the health of the synovial membrane (joint lining) and the cartilage within it.

"The best treatment plan for osteoarthritis should include both a disease-modifying medication (such as HA or PSGAG) and a symptom-modifying medication (such as phenylbutazone, or Bute)," Palmer recommended.

The last joint medication study Palmer discussed evaluated topical diclofenac cream (Surpass) applied to knees with experimentally induced osteoarthritis in comparison with oral phenylbutazone. He reported that diclofenac cream (7.3 g applied twice daily) had both symptom-modifying and disease-modifying effects, while phenylbutazone (2 g given orally once daily) had only symptom-modifying effects (it decreased inflammation, but did not improve the health of the joint).

References:

Kay, A.T.; Bolt, D.M.; Ishihara, A.; Rajala-Schultz, P.J.; Bertone, A.L. Anti-inflammatory and analgesic effects of intra-articular injection of triamcinolone acetonide, mepivacaine hydrochloride, or both on lipopolysaccharide-induced lameness in horses. American Journal of Veterinary Research 2008;69:1646-1654.

Frisbie, D.D., et al. Evaluation of polysulfated gylcosaminoglycan or sodium hyaluronan administered intraarticularly for treatment of horses with experimentally induced osteoarthritis. American Journal of Veterinary Research 2009;70:203-209.

Frisbie, D.D.; McIlwraith, C.W.; Kawcak, C.E.; Werpy, N.M.; Pearce, G.L. Evaluation of topically administered diclofenac liposomal cream for treatment of horses with experimentally induced osteoarthritis. American Journal of Veterinary Research 2009:70:210-215.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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