2011's Top Equine Surgery/Lameness Studies

Each year, researchers publish hundreds of equine surgery and lameness studies. During the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas, some of the most clinically relevant surgery and lameness studies were presented during the annual Kester News Hour. Scott E. Palmer, DVM, Dipl. AVBP (Equine Practice), hospital director and staff surgeon at the New Jersey Equine Clinic, shared his thoughts on top studies with a veterinary audience.

Respiratory Problems

"Coughing is a common complaint in mature nonracehorses with epiglottic abnormalities," began Palmer as he described a retrospective study of mature (a mean age 16, with a range from 9 to 30 years of age) horses with abnormalities of the epiglottis (a flap of cartilage that moves to cover the horse's windpipe when it swallows to prevent inhaling fluid or food). In the 23 horses studied, the primary complaint for 70% was chronic cough and the most common epiglottic abnormality was epiglottic entrapment, which results in hampered epiglottal movement (followed by subepiglottic granuloma and subepiglottic cyst). All horses were treated surgically and 74% required no further treatment, while a few required further treatment for inflammation, recurrent airway obstruction, and dorsal displacement of the soft palate.

"Upper airway endoscopy is recommended in the evaluation of older horses with a cough," summarized Palmer. "Surgical treatment can be beneficial in most horses, with some requiring further postoperative medical treatment."

Not long ago, dynamic or overground airway endoscopy (performed while the horse works normally) was but a dream, with standing and treadmill endoscopy being the only ways to simply evaluate the horse's airway. In the few years that have passed since the release of a practical backpack-based system for examining the horse's airway during normal exercise, researchers have been reevaluating accepted knowledge about equine respiratory problems and working to develop optimal workouts for revealing abnormalities.

Researchers at the U.K.'s University of Bristol recently published their investigation of dynamic endoscopy exams and the workouts used during those exams. Of note was that airway noise was the easiest condition to reproduce on examination, and poor performance without noise was the most difficult.

Palmer concluded, "A principal advantage of dynamic videoendoscopy is the ability to evaluate the horse in its natural surroundings and under race conditions. However, it may be difficult to standardize exercise tests in the field under widely varying conditions. It is best to replicate race conditions as closely as possible with peers (working alongside); no single protocol is likely to be appropriate for all exams."

Laryngoplasty, also called tieback surgery, is a relatively common treatment for horses that make significant airway noise during exercise (roaring). The surgery, which involves placing 1 or 2 sutures in the left arytenoid cartilage to abduct or hold it out of the airway, is usually effective but as with most treatments its success rate isn't 100%. Researchers at the University of Pennsylvania examined records of 45 horses that had had left laryngoplasty surgery over a 15-year period to see if collapse of the cartilage after surgery could be predicted from post-procedure resting endoscopy, and to explain why some horses continue to perform poorly after surgery.

Palmer reported that horses with no post-surgical abduction tended to have left arytenoid collapse, but horses with moderate or good degree of abduction showed no predisposition to collapse.

"Complex obstructions causing respiratory noise were observed in most examinations, but they were not specific for arytenoid collapse," Palmer added. "While some of (the observed) conditions may be diagnosed with a resting endoscopic examination, these data underscore the value of performing a dynamic examination prior to surgery in order to identify conditions that may compromise the outcome of laryngoplasty."

Looking inside the airway is, of course, useful for diagnosing/evaluating respiratory problems, but what about looking in from the outside? Researchers from Rood & Riddle Equine Hospital, in Lexington, Ky., investigated whether performing an ultrasound examination of the larynx from the outside of the horse's neck could help diagnose abnormal arytenoid cartilage movement, and they found that it was indeed a useful method. Abnormal muscles moving the arytenoid cartilage had increased echogenicity (were "denser") on ultrasound; thus, ultrasound was found to be 90% sensitive for detecting the condition and 98% specific for ruling out other conditions. This is better even than treadmill endoscopy, which was 80% sensitive and 81% specific.

"Ultrasonography is a valuable addition to the diagnostic evaluation of abnormal arytenoid movement and may be extremely valuable for case selection, particularly in an effort to make a differential diagnosis between early arytenoid chondritis (arytenoid chondropathy, an uncommon acquired condition that can lead to airway obstruction) and laryngeal hemiplegia," noted Palmer.

Sinus infections in horses can be just as tough to get rid of as those in humans. Palmer reviewed an Equine Veterinary Journal study in which veterinarians documented long-term health of horses following conservative treatment (such as standing procedures to drain/remove pus and rinse the sinus ) for various types of sinus disease-.

Long-term results were mostly positive, with 91% of horses cured and usually after only one treatment. The exception to this rule was sinus neoplasia (tumor, 22% cured).

"More conservative treatments, including removal of intrasinus inspissated (thickened) pus by sinoscopy, pre-existing sinonasal fistula, or sinusotomy, which avoid the risk and expense of general anesthesia are often effective for management of chronic primary sinus disease in many cases," reported Palmer.

REFERENCES
Aitken MR, Parente EJ. Epiglottic abnormalities in mature nonracehorses: 23 cases (1990-2009). J Am Vet Med Assoc 2011;238(12):1634-1838.
Allen KJ, Franklin SH. Assessment of the exercise tests used during overground endoscopy in UK Thoroughbred racehorses and how these may affect the diagnosis of dynamic upper respiratory tract obstructions. Equine Vet J Suppl 2010;42(38):587-591.
Davidson EJ, Martin BB, Rieger RH, et al. Exercising videoendoscopic evaluation of 45 horses with respiratory noise and/or poor performance after laryngoplasty. Vet Surg 2010;39(8):942-948.
Garrett KS, Woodie JB, Embertson RM. Association of treadmill upper airway endoscopic evaluation with results of ultrasonography and resting upper airway endoscopic evaluation. Equine Vet J2011; 43(3):365-371. 
Dixon PM, et al. Equine paranasal sinus disease: A long-term study of 200 cases (1997-2009): Treatments and long-term results. Equine Vet J 2011. 

Treating Infected Joints

"Septic (infected) arthritis is commonly treated with intravenous (IV) and regional (antibiotic) perfusion in conjunction with joint lavage (flushing)," began Palmer as he discussed a study of tourniquet types. For regional limb perfusion, a veterinarian places a tourniquet on the leg for a short time to stop blood from flowing back up the limb before injecting antibiotic below the tourniquet. This allows the antibiotic to concentrate at very high levels in the bloodstream below the touriquet, perfusing the tissues. Theoretically, performing the joint lavage simultaneously with the regional limb perfusion could cause loss of the antibiotic in the joint and thus compromise the treatment.

"In standing horses, IV regional limb perfusion performed simultaneously with joint lavage resulted in negligible loss of amikacin in the egress lavage fluids (the less antibiotic lost, the better)," Palmer reported. This study validated the positive effect of the simultaneous use of these two treatments for joint infection. "Additionally, the Esmarch tourniquet was more effective in preventing loss of amikacin from the distal portion of the limb, easier to use, and less expensive than the pneumatic tourniquet."

REFERENCES
Alkabes SB, Adams SB, Moore GE, et al. Comparison of two tourniquets and determination of amikacin sulfate concentrations after metacarpophalangeal joint lavage performed simultaneously with intravenous regional limb perfusion in horses. Am J Vet Res 2011;72(5):613-619. 

Stem Cells

An increasing number of veterinarians are using stem cell therapy in horses, and veterinarians need a safe, efficient technique for harvesting bone marrow for stem cells. In a recent Equine Veterinary Journal study authors described such a technique that involves placing a Jamshidi needle (a cylindrical needle with a tapered cutting tip) into the fifth sternebra (one of the segments of the sternum) with ultrasound guidance. Palmer noted that this procedure "enables aspiration of bone marrow reliably with minimal damage to the sternum and risk to the horse."

When harvesting bone marrow for stem cells, practitioners have two options for a harvest site: The sternum (breastbone) and the ilium (hip). In a Colorado State University study researchers compared the quality of samples retrieved from both sites and found no significant difference between them (although the first sample from each site had significantly more stem cells than the second), so practitioners can choose the site they prefer and obtain the same quality of stem cells.

"Both the sternum and the ilium offer a rich supply of stem cells that have similar growth rate characteristics," Palmer summarized.

"Long-term follow-up (after stem cell usage) is hard to find," said Palmer. He discussed a study of stem cell usage in which the researchers followed 141 racing Thoroughbreds (flat and steeplechase) for at least two years after returning to full work following stem cell treatment of superficial digital flexor tendon injuries.

"Tendon lesions filled in quickly, histological (tissue architecture) appearance showed well-aligned fibrils, and there was an absence of scar tissue," he described. "Ninety-eight percent returned to racing with a 26% re-injury rate in hunt horses and 50% in flat horses. There was no correlation between outcome and age, discipline, number of stem cells injected, or injury-to-implantation interval (factors that were thought to be important previously).

"This study shows that marrow-derived mesenchymal stem cell implantation is safe and appears to reduce re-injury rate after superficial digital flexor injury, especially in National Hunt racehorses," he concluded. "It is the first report that provides evidence for long-term efficacy of mesenchymal stem cell treatment for tendinopathy (tendon disease) in racehorses. However, the long-term success in the Thoroughbred flat horse remains a challenge."

Stem cell therapy is often considered a form of regenerative medicine, resulting in healing of injuries with tissue that is superior to the scar tissue found in traditionally healed injuries. Palmer discussed a study in which scientists set out to determine whether stem cells actually resulted in architecturally superior healing by evaluating collagen fibril size in tendon injuries treated with stem cells.

"The matrix of normal, uninjured superficial digital flexor tendon consists of populations of small- and large-diameter collagen fibrils," explained Palmer. "Injured tendon healed with a prominence of small-diameter fibrils, regardless of whether lesions were treated with bone marrow-derived mesenchymal stem cells at four weeks. We still have a lot to learn about this."

The study authors noted, "Favoring matrix regeneration (restoring the tendon to its original architecture) over fibrotic repair (filling the defect with a scar) may not be the mechanism by which autologous mesenchymal stem cells assist healing of tendon injury."

If you're using stem cells to treat tendon lesions, they need to reach and stay in the lesion, and the route of stem cell administration (intravenous, intralesional, or regional perfusion) has a lot to do with that. Royal Veterinary College (in the U.K.) researchers compared the three methods of administering stem cells and found that intralesional injection of stem cells (directly into the lesion) was the most effective for keeping stem cells within the lesion after 24 hours (the lesion retained 10% of cells), while regional perfusion came in a close second with cells remaining in the lesions of 11 of 12 horses. In contrast, stem cells injected intravenously did not "home" on the lesions at all, instead scattering mostly around the lungs.

"Regional perfusion is a viable alternative if no core lesion (single obvious injury) is present," commented Palmer.

When injecting stem cells into a horse (or any other mammal, for that matter), it might seem logical to also inject a little antibiotic just in case, to prevent an infection developing from any pathogens you might introduce. However, the clear message from a recent study is that this can be a very bad idea: Don't mix stem cells with either gentocin or amikacin antibiotic, as they kill the stem cells. In this study researchers found that those two antibiotics killed more than 95% of the injected stem cells after 45 minutes and two hours, respectively.

However, incubating stem cells with hyaluronic acid and penicillin/streptomycin resulted in acceptable stem cell viability of 80%.

REFERENCES
Kasashima Y, Ueno T, Tomita A, Goodship AE, Smith RKW. Optimisation of bone marrow aspiration from the equine sternum for the safe recovery of mesenchymal stem cells. Equine Vet J 2011;43(3):288-294.
Adams MK et al. Equine bone marrow-derived mesenchymal stem cells: Comparing the sternum and the ilium. In Proceedings, Am Coll Vet Surg Symposium 2011.
Godwin EE, Young NJ, Dudhia J, et al. Implantation of bone marrow-derived mesenchymal stem cells demonstrates improved outcome in horses with overstrain injury of the superficial digital flexor tendon. Equine Vet J 2011;43(3).
Schramme MC, et al. The effect of intralesional bone marrow derived mesenchymal stem cells and bone marrow supernatant on collagen fibril size in a surgical model of equine superficial digital tendonitis. In Proceedings, Am Coll Vet Surg Symposium 2011.
BecerraP, et al. In vivo tracking of injected mesenchymal stem cells using Technetium-99m. In Proceedings, Am Coll Vet Surg Symposium 2011. 
Bohannon L, et al. The effects of mixing pharmaceuticals with equine stem cells prior to treatment of orthopedic injuries in the horse. In Proceedings, Am Coll Vet Surg Symposium 2011.

Wound Healing

Made from bees frequenting the manuka bush of New Zealand, manuka honey gel is a recent rage in wound healing products. Researchers at the University of Sydney, in Australia, studied the gel made from pure manuka honey and a water-based gel (made into a thick gel to avoid the need for bandaging to keep the honey in contact with the wound). They found that while it had no appreciable effect on contaminated wounds, it did quite well on noncontaminated wounds; these wounds treated with pure manuka honey or manuka honey gel healed faster than control wounds until Day 35, and manuka honey gel-treated wounds healed faster than all other wounds.

"You can save lot of money on bandaging materials with this (the manuka honey gel), but it seems counterintuitive for use in warm weather when insects can be a problem," commented Palmer.

REFERENCES Bischofberger AS, et al. The effect of short and longer-term treatment with manuka honey gel on second intention healing of wounds contaminated with feces and non-contaminated wounds on the distal aspect of equine forelimbs. In Proceedings, Am Coll Vet Surg Symposium 2011. 

Colic

"Recurrent colic is often discussed but not well-documented," noted Palmer, as he described a University of Liverpool study on the condition and risk factors for it. In this study nearly 37% of horses with medically (not surgically) treated colic had another colic episode within the next year.

"Recurrence of colic was higher than previously reported," he commented. "Horses with a known dental problem or cribbing/windsucking were at increased risk of recurrence. This confirms long-held beliefs and gives us a baseline number to share with clients when treating medical colics in the field."

Another colic recurrence study, this one on colic recurrence after colic surgery, found a higher recurrence rate of more than 50%.

"The prevalence of subsequent episodes of colic in horses undergoing exploratory surgery (also known as laparatomy, making a large incision through the abdominal wall to gain access to the abdominal cavity) may be higher than previously estimated," Palmer commented. "The incidence of colic in this large population of horses following exploratory laparotomy (54.4%) is far greater than the estimated rate within the general equine population."

Diagnosing strangulating bowel lesions associated with colic isn't always easy; the horse's torso is quite large and capable of "hiding" some deep lesions such as bowel twists severe enough to cut off blood flow . However, a recent study provided insight on a simple test that can help identify strangulating bowel lesions that require immediate surgical intervention.

In the study of 94 horses with colic, rising concentrations of lactate in peritoneal (abdominal cavity) fluid (sampled via a "belly tap") over a 30-minute period were found to be a "good indicator of strangulating lesions, easily performed, sensitive (79%), specific (88%), and a good indicator of the need for surgery," said Palmer. "Unrelenting pain will always be a primary factor, but this test can help in more ambiguous cases."

Right dorsal displacement of the large colon and/or 180-degree volvulus (half twist) is another cause of severe colic, and it's one that can be visualized with ultrasound. Palmer described a study in which authors explained the ultrasound technique.

"Ultrasonic visualization of colonic mesenteric vasculature (blood vessels supplying the large colon) adjacent to the right body wall was found to be highly specific and sensitive for the detection of right dorsal colon displacement and/or 180-degree colon volvulus in horses," he said. This non-invasive and practical test can help determine the need for surgery in cases of right colon displacement.

REFERENCES
Scantlebury CE, Archer DC, Proudman CJ, et al. Recurrent colic in the horse: Incidence and risk factors for recurrence in the general practice population. In Proceedings, Colic Research Symposium 2011. 
Burford JH, Tudur-Smith C, Smith J, et al. The incidence of post-operative colic in 1412 horses discharged following exploratory laparotomy for investigation of acute gastrointestinal disease. In Proceedings, Colic Research Symposium 2011;126.
Peloso JG, Cohen N. Using serial peritoneal lactate in referred horses with signs of colic to identify strangulating intestinal lesions. In Proceedings, Colic Research Symposium 2011;105.
Ness SL, et al. Ultrasonic visualization of colonic mesenteric vasculature as an indicator of large colon right dorsal displacement and/or 180 degree vovulus in horses. In Proceedings, Colic Research Symposium 2011;128.

Racing Injuries

"The majority of fatal musculoskeletal injuries in racehorses occur in the fetlock joint, and routine screening often fails to detect lesions beforehand," said Palmer as he described a study of whether standing magnetic resonance imaging (MRI) could detect early bone pathology that could lead to fractures.

"In this study, 35.8% of Thoroughbred horses with lameness localized to the fetlock region had MRI findings consistent with fracture pathology that was not evident radiographically (on X-rays)," he reported. "Only 5% had no lesions. Therefore it appears likely that scanning race horses with fetlock lameness with Low-field standing MRI has the potential to reduce the incidence of catastrophic fractures."

In another Thoroughbred study researchers used nuclear scintigraphy (often called a bone scan) to evaluate fetlock lameness, and they found that about half of the horses had increased radiopharmaceutical uptake (IRU, indicative of bone remodeling, usually in response to injury) in the distal cannon condyles (end of the cannon bone at the fetlock). Sixty-two of the 220 horses studied had moderate to marked IRU, more commonly in forelimbs than hind limbs, and these horses had fewer starts in races, earned less money, and were slower to return to racing after a rest period than uninjured horses.

"Overload of the metacarpophalangeal/metatarsophalangeal condyles (in forelimbs and hind limbs) is a common and significant problem of Thoroughbred racehorses that is readily identified with scintigraphy," said Palmer. "The simple presence of increased radiopharmaceutical uptake in the condyles was a common and clinically significant finding in racehorses with fetlock lameness, but was not found to be associated with the development of condylar fractures, as was previously thought."

The final study Palmer covered was one evaluating turnout as a treatment for cumulative stress-induced bone injury of the distal cannon bone condyles. In this study 55 racehorses with lameness and increased IRU in the fetlocks were turned out for 60-150 days, and then they were turned out for one to three months longer if they remained lame after their turnout period.

"Nearly twice as many horses resumed racing compared to earlier reports," he revealed. "About one-third improved their performance, one-third stayed the same, and one-third performed worse.

"Paddock turnout is a reasonable strategy for managing palmar/plantar cannon disease without severe lesions; however, horses with semilunar articular (joint surface) fractures had a reduced prognosis for racing," he concluded.

REFERENCES
Powell SE. Low-field standing magnetic resonance imaging findings of the metacarpo/metatarsophalangeal joint of racing Thoroughbreds with lameness localized to the region: A retrospective study of 131 horses. Equine Vet J 2011. 
Trope GD, Anderson GA, Whiton RC. Patterns of scintigraphic uptake in the fetlock joint of Thoroughbred racehorses and the effect of increased radiopharmaceutical uptake in the distal metacarpal/tarsalcondyle on performance. Equine Vet J 2011;43(5):509-515. 
Tull T, Bramlage LR. Racing prognosis after cumulative stress-induced injury of the distal portion of the third metacarpal and third metatarsal bones in Thoroughbred racehorses: 55 cases (2000-2009). J Am Vet Med Assoc 2010;238(10):1316-1322. 

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

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