Top Equine Surgery Studies of 2012 (AAEP 2012)

Equine practitioners are undeniably busy individuals, making farm calls, caring for patients, and evaluating test results on a daily basis. To help veterinarians keep up to date on the most recent and relevant research, three veterinarians review the top studies in the fields of surgery, medicine, and reproduction at the annual American Association of Equine Practitioners' convention. This ever-popular session, called the Kester News Hour, kicked off the 2012 convention, held Dec. 1-5 in Anaheim, Calif.

Lisa A. Fortier, DVM, PhD, Dipl. ACVS, associate professor of Large Animal Surgery at Cornell, University's College of Veterinary Medicine in Ithaca, N.Y., highlighted the year's top equine surgery-related studies.

Upper Respiratory Topics

Fortier began by discussing some of the first published studies in which researchers examined the use of dynamic videoendoscopy (in which the horse undergoes the exam while exercising on a high speed treadmill or working under saddle) to evaluate equine upper respiratory issues. In one study researchers used the relatively new technology to evaluate 129 performance horses presented for evaluation of exercise noise or decreased performance; researchers fitted the horses with a videoendscope before exercise riders put the animals' through their normal routines. Study results showed that 91% of horses presenting with exercise noise and 71% of those presenting with poor performance were diagnosed with some type of dynamic airway obstruction (such as structural collapse; axial deviation of the aryepiglottic fold; and dorsal displacement of the soft palate, or DDSP). What's more, Fortier said, the obstructions--with the exception of DDSP--worsened during times of "increased rider intervention," such as head flexion, spurring, circling, or jumping. Additionally, Fortier said, all of the dynamic airway obstructions identified via videoendoscopy were associated with both upper and lower airway inflammation. Fortier stressed that veterinarians should treat underlying airway inflammation in these cases.

Dynamic videoendoscopy might provide a new way for veterinarians to evaluate the respiratory tract, but does the instrument itself impact horses' performance? The researchers conducting the next study Fortier described asked just that. The team examined Standardbred horses in sanctioned harness races using videoendoscopy and confirmed they could detect the presence of upper airway disorders without disrupting performance.

"This study further supports the use of dynamic endoscopy to understand what is happening in the upper respiratory tract during exercise with the horse in its natural environment as opposed to during a treadmill exam," she said. However, if a treadmill exam is the only option, then veterinarians should incorporate the study of head flexion into the research, she relayed, so they can evaluate the horse's airway in the normal circumstances in which the animal works.

Finally, Fortier discussed a study in which researchers evaluated how three degrees of soft palate dysfunction--mild, moderate, and severe--affected respiratory parameters. The team evaluated 40 Thoroughbred racehorses in training presented for recurrent palate instability (movement of the soft palate without displacement of its caudal border) and found that even abnormalities considered mild or moderate yielded negative effects on respiratory parameters. Specifically, Fortier said, affected horses had "decreased end tidal carbon dioxide and oxygen levels," indicating these obstructions impeded the horses' breathing.

"These results indicate that respiratory parameters should be considered along with subjective endoscopic observations to fully understand the clinical ramifications of observations that are subjectively judged as mild or moderate," she concluded.

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Orthopedic Therapies

Fortier then shifted focus and discussed several studies pertaining to orthopedic treatments, the first of which involved distal (lower) hock arthritis. She said this was the first prospective study in which researchers evaluated the safety and efficacy of alcohol-facilitated ankylosis (joint fusion) in arthritic lower hock joints; "proof of concept" studies have previously been carried out on healthy horses, she noted. In the current study, the team performed ankylosis (with 70% alcohol) on 21 horses with confirmed hock arthritis. The study revealed that 85% of the horses were not lame after three months, and 90% were sound at one year post-procedure. Fortier cautioned that about 30% of the time, researchers could not enter the distal intertarsal joint (DIT, one of the four joints in the hock) to perform the injection, and that 45% of injected DIT joints "communicated" with the proximal intertarsal joint (another joint in the hock) and tibiotarsal joint (the major motion joint of the hock). This means that veterinarians should use caution when considering alcohol injections because leakage of alcohol into the tibiotarsal joint could lead to ankylosis there, as well, which would be detrimental to the horse.

The results of a second study Fortier discussed, in which researchers investigated alcohol for fusion of the lower hock joints, showed that 52% of osteoarthritic horses that had not responded to corticosteroid treatment improved in the short term after injection; however, the condition of 19% of those animals deteriorated significantly six to nine months post-ankylosis. Study researchers believe this occurred because the horses were more clinically challenged (i.e., bilateral cases of arthritis or more cases of advanced disease than in other studies).

Referring to both alcohol-facilitated ankylosis studies, Fortier cautioned that while the procedure is effective in fusing joints, it also poses drawbacks and should not be used as a first-line treatment option, given the complications highlighted by these studies. In addition, veterinarians should perform contrast arthrography (joint evaluation) before each injection and, perhaps, they should only inject the tarsometatarsal joint to minimize alcohol leaking into the main hock joint.

Finally, Fortier discussed a study in which practitioners evaluated alternative routes for administering mesenchymal stem cell (MSC). In some cases in which clinicians desire a greater distribution of stem cells--for example, where there isn't a core lesion (single obvious injury) or where there is a diffuse lesion (injury that is spread out over an area)--they need to establish a regional delivery route of MSCs. The research team administered stem cells labeled for tracking purposes via intravenous (IV) and intra-arterial injection in six horses, using regional limb perfusion. They found that both IV and intra-arterial injections had good distribution in the carpus (knee) and metacarpus (cannon bone), and that the intra-arterial approach was more effective for distributing MSCs to the pastern and hoof than the IV approach. She cautioned that intra-arterial injections resulted in "severe thrombosis" (blood clotting in the veins) in one horse.

"This suggests that IV delivery of stem cells is the safer route of administration and that, perhaps, if delivery of stem cells to the pastern or foot is desired, then the cells should be delivered more closely to the target via IV injection below the carpus," she concluded.

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Colic

Fortier then switched gears to discuss several studies on colic. In the first, researchers evaluated how visualizing colonic mesenteric vasculature (the ability to see blood vessels supplying the large colon) on abdominal ultrasound might indicate right dorsal colon displacement, a 180° volvulus (twist), or both. The team performed abdominal ultrasound on 82 horses before confirming their diagnosis via surgery. Researchers concluded the test has a 68% sensitivity (these are true positives, meaning that when clinicians see vessels on ultrasound there is a 68% chance that horse will have a displacement or volvulus) and 98% specificity (these are true negatives, meaning that 98% of horses whose vessels are not apparent on ultrasound do not have a displacement). On that basis, she recommended practitioners implement abdominal ultrasound in their colic examinations. She cautioned that before becoming competent in this technique, veterinarians must familiarize themselves with cecal vascular anatomy, which runs ventral to the right paralumbar fossa (flank) and follows the curvature of the last rib.

Next, Fortier discussed a study in which scientists evaluated the success rates of treating horses medically for suspected right or left dorsal colon displacement. The retrospective study included 116 cases of suspected large colon volvulus and showed that clinicians were 64% successful in managing presumed right colon displacement medically and 76% successful in treating suspected left colon displacement with medical approaches. If surgery was needed, Fortier said, roughly 94% survived to discharge. With this study researchers showed that most affected horses will respond favorably to medical therapy, she relayed.

Fortier also touched on a study in which researchers assessed the long-term survival rates of horses with large colon volvulus. The team evaluated the two-year survival rates of 116 horses, and they found that 20% did not recover from surgical anesthesia and 71% survived to discharge. Of the latter, 48% survived one year past discharge and only 34% survived two years past discharge. Fortier stressed that veterinarians should refer such cases early to expedite treatment and/or surgery because increased preoperative packed cell volume was strongly associated with decreased survival.

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Racehorse Topics

In her final segment, Fortier discussed several studies surrounding racehorse health. Researchers on the first paper evaluated the incidence of racehorse injury among different trainers. The team found that 25% of the 647 horses under the care of 13 trainers at six different racetracks sustained a carpal, metacarpophalangeal, and/or metatarsophalangeal (knee and/or fetlock) injury during training; further, there were significant differences in injury rates, location, and severity among the trainers.

"Understanding the differences in training protocols between trainers might lead to methods to decrease injury," she said. "This might include not only exercise, but training surface, shoeing, medication, and rider."

In the next study Fortier discussed, scientists had evaluated if there was an association between career length and age of first start among a population of racehorses. A research team evaluated the race records of more than 117,000 Australian Thoroughbreds and found that horses' risk of retirement was actually lower if horses began racing at 2, had more starts at 2, and ran at longer distances. This suggests that there are no apparent detrimental effects of racing as a 2-year old, she said.

The final study Fortier presented involved subclinical (nonapparent) defects in non-lame Thoroughbred racehorses' suspensory ligaments as identified with ultrasonography. Two reviewers evaluated ultrasound images from 60 racehorses at the end of a full race season, and they found mild defects (Grade 1) in 26% of horses and moderate defects (Grade 2) in 7% of horses. The reviewers did not find any defects that could be classified as severe (Grade 3), she said. Further, on follow-up examination, Fortier noted that only one Grade 2 horse's defects had progressed to a clinical problem.

"This suggests that ultrasound findings are not always correlated with disease and a false diagnosis of suspensory ligament desmitis could negatively affect sales," she concluded. "If suspensory branch lesions are identified on ultrasound examination, further methods of evaluation such as a full lameness examination should be performed to understand the clinical significance of the ultrasound findings."

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Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.