2010's Top Equine Lameness/Surgery Studies (AAEP 2010)

What would be your pick for the most groundbreaking news in equine lameness, surgery, or racing for 2010? Not sure? Read on to find out what Scott E. Palmer, VMD, Dipl. ABVP (Equine Practice), hospital director and a staff surgeon of the New Jersey Equine Clinic in Clarksburg, N.J., and past president of the AAEP and American Board of Veterinary Practitioners, deemed the most important news in these areas in 2010. He presented this discussion during the Kester News Hour session to help kick off the 2010 American Association of Equine Practitioners Convention, held Dec. 4-8 in Baltimore, Md.

Diagnostic Techniques

Veterinarians are always looking for improved diagnostic methods. Palmer discussed several studies on diagnostic techniques, including one study from Equine Veterinary Journal (EVJ) in which researchers compared different culture techniques for growing bacteria from synovial (joint) fluid. They found that use of enriched blood culture media increased the likelihood of obtaining a positive culture, which can help veterinarians be more successful in treating joint infections.

The second study correlated bacterial cultures from synovial fluid to survival rates of horses with joint infection. "Twenty-one percent of horses with positive cultures (containing bacteria) were euthanized vs. 1.4% of controls," commented Palmer. He also noted that horses with Staphylococcus aureus cultured from their joints did not fare as well as those without.

Another EVJ study evaluated the potential use of biomarkers found in a horse's serum for predicting musculoskeletal injury. "Biomarkers have the potential to be used as a screening aid prior to musculoskeletal injury," wrote the authors. The researchers found seven markers that often correlated with injury, and that were deemed "promising but still not ready for prime time" according to Palmer.

Another potential screening tool was discussed in an AJVR study where researchers investigated whether fragments of certain types of collagen (a structural protein) found in synovial (joint) fluid and/or serum might indicate joint injury in that horse. The investigators determined that levels of these collagen fragments in serum and synovial fluid, along with the ratio between them, "could be used to detect horses with joint injury," wrote the authors.

Palmer also discussed a study of diagnostic analgesia (nerve blocks) in horses, specifically the low four-point block used to numb structures at and below the fetlock joint. The researchers' goal was to determine if this block might also inadvertently anesthetize other structures higher in the limb, using contrast radiography to see where the anesthetic solution might spread after injection. They found that anesthetic from this block was unlikely to spread upward and anesthetize the upper cannon bone region. They also noted that the deep digital flexor tendon sheath was often inadvertently punctured when performing this block. "For this reason, It's extremely important to use aseptic technique (when performing this block)," advised Palmer.

An EVJ study on flexion tests for localizing lameness to the fetlock joint found that pain in the fetlock joint itself was most likely to contribute to a positive test. The researchers found that flexion of the distal interphalangeal joints was unlikely to cause a positive flexion test in normal horses and urged veterinarians and horse owners to interpret positive fetlock flexion tests with caution during a pre-purchase examination.

However, Palmer commented, "Don't throw the baby out with the bathwater." In his experience, inflammation of the coffin joint can also result in a positive flexion test in some cases. Palmer felt that the flexion test remains an important part of the pre-purchase examination.

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Racing Topics

Palmer discussed a number of studies on racehorses, including one in the American Journal of Veterinary Research (AJVR) on the effects of early exercise on future soundness. "Moderate, controlled exercise can be safe at an early age (from 3 weeks to 18 months of age)," summarized Palmer. Indeed, the authors of this study suggested that early exercise might even help protect joints from future injury (although more research is needed).

Another report presented during the Jockey Club Safety and Welfare Summit in 2010 (based on information in the Equine Injury Database) looked at racing surfaces (i.e., turf [grass] vs. dirt vs. synthetic). Palmer described four myths dispelled by this preliminary study:

  • Myth 1: Synthetic surfaces reduce fatal musculoskeletal injury (no difference was actually found)
  • Myth 2: Injuries occur when horses move from turf to other surfaces (the data disagree).
  • Myth 3: 2-year-old horses are at greater risk of injury than older horses (the data say it's the other way around).
  • Myth 4: Fillies are at greater risk of injury than colts (again, the data say the opposite is true).

"One thing is for sure: Track maintenance is key," said Palmer.

Identifying horses at risk for fracture at the racetrack is a high priority. In the past year a number of papers compared diagnostic techniques for detection of changes in bone that might predispose a horse to fracture.

An AJVR study investigated proximal sesamoid bone fractures (behind the fetlock) and found that racehorses with these fractures had evidence of excessive remodeling and porosity of their sesamoid bones that likely predisposed these horses to complete fracture and catastrophic injury. The authors also suggested that detection of these focal areas of injury/remodeling could help to identify horses at risk for this type of fracture and prevent catastrophic injury (i.e., by not racing horses with this type of injury as they are more likely to break down).

Another study that evaluated early injury detection by use of scintigraphy (bone scan) in racehorses found increased radio-isotope uptake (indicating bone remodeling) in the lower joint surface of the cannon bone. Researchers on this study (published in EVJ) found that scintigraphy was good for detecting horses with this early bone injury, but it did not help veterinarians determine which horses should safely continue in training and which ones should be taken out of training to prevent further injury.

Yet another study focusing on the early detection of bone damage in the fetlock joint compared digital radiography, magnetic resonance imaging and computed tomography as screening techniques to identify changes in the cannon bone that often lead to fracture. Researchers found that digital radiography underestimated such damage, while computed tomography (CT) and magnetic resonance imaging (MRI) were able to detect it. Unfortunately, CT and MRI with high-resolution capability require use of general anesthesia, which prevents them from being used as routine screening tools.

"Standing MRI may be a good tool [for identifying horses at risk for fracture], but it is very operator-dependent and false negative results are a significant concern," Palmer commented.

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Musculoskeletal Therapy

Finding problems is important, and so is treating them properly. Palmer next discussed treatments for a number of musculoskeletal problems, starting with a review of literature on the use of corticosteroids for reducing joint inflammation in the horse (published in EVJ).

"Intra-articular corticosteroids (injected within the joint) are a hot button in practice," Palmer commented. "Used in conjunction with disease-modifying medications like hyaluronic acid, they are extremely useful to reduce joint inflammation."

Another study on corticosteroids (in AJVR) evaluated whether triamcinolone acetonide (TCA) injected into the coffin (distal interphalangeal) joint would diffuse into the navicular bursa (thus potentially medicating both areas). The researchers found that TCA did migrate into the navicular bursa of sound horses, even when hyaluronic acid was mixed with it. This strategy "can potentially be used for treatment of navicular syndrome, but further studies are needed," wrote the researchers.

One such study was presented during the ACVS symposium and evaluated the same question in horses with clinical navicular syndrome. The authors of this paper found that diffusion of TCA from the coffin joint to the navicular bursa worked in clinical cases as well as in normal horses.

The next study he discussed evaluated the use of intra-articular vs. intravenous morphine for experimentally induced synovitis (joint inflammation), and found that the intra-articular route was more effective in reducing lameness."Intra-articular morphine treatment may be a useful adjunct to other pain management modes after a painful joint surgery," Palmer noted.

Stem cells are a hot topic for treating various injuries, and two studies focused on this area. One published in EVJ compared embryonic stem cells and mesenchymal stromal (bone marrow) cells in terms of their behavior when injected into an experimentally induced injury in the superficial digital flexor tendon. Researchers found that embryonic stem cells did not cause immune reactions in the 90-day study period, and they migrated to other areas of damage while mesenchymal stromal cells did not.

The second stem cell study also supported the use of embryonic stem cells for healing tendon injuries, noted Palmer.

The final study he discussed evaluated the use of biophosphonates in horses; this class of drug is used to prevent bone loss (for example, to prevent or combat osteoporosis in older women). In horses, it has been used to treat navicular syndrome, subchondral bone cysts, osteoarthritis, stress remodeling and other lameness conditions. This study, published in the ACVS Proceedings, evaluated the use of zoledronic acid for treatment of 23 horses with a variety of lameness conditions and reported that 16 of them returned to their original use.

"Zoledronic acid may be useful to treat certain lameness conditions, but controlled studies are warranted," noted Palmer. "We don't know a lot about this medication. It's being used to treat a variety of conditions in horses in the belief that it will decrease osteolytic (bone-destroying) processes that may contribute to lameness problems in horses, some of which may play a role in catastrophic injury.

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Additional Topics

Palmer also discussed a few surgical techniques and other studies as follows:

  • One study in AJVR on common wound flushing techniques found that the ideal fluid pressure for flushing joints was best achieved by use of a one-liter bag and pressurized cuff. Use of syringes to flush wounds can produce high enough fluid pressures to damage tissues.
  • A Journal of the American Veterinary Medical Association study on a technique for partial phallectomy (partial removal of the penis) found that linear urethrostomy followed by placement of a band tourniquet above the area of disease or injury, then removal of the part of the penis below the tourniquet, was an effective method. "This can be done in the standing horse, which is good for older or debilitated horses that can't undergo general anesthesia," said Palmer.
  • Mitomycin C was found to be effective for combating squamous cell carcinomas near equine eyes in a Veterinary Record study, whether used alone or in conjunction with surgical removal of the lesion.
  • Researchers in one study published in Veterinary Surgery found that the interior of mares' abdomens could be easily and safely visualized by inserting an endoscope through a small incision made in the vagina (thus creating no external incisions). Palmer reported that the technique provided good visibility of abdominal contents and the incisions healed without incident.
  • One study discussed a surgical technique for stitching together the ends of a severed tendon. This novel technique required patience to learn, said Palmer, but it showed superior strength to conventional suture patterns.
  • Lastly, Palmer referenced a study on cryotherapy (cold therapy) for treating laminitis. This study found that ice bags and water boots each cooled blood within the blood vessels of the foot by 20 degrees (F) for a two-hour period. The study was also discussed during the AAEP's Joints and Foot Lameness session.

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Further Reading

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

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