Top Surgery Studies
One of the most popular sessions at each American Association of Equine Practitioners (AAEP) convention is the Kester News Hour, which features three renowned veterinarians sharing their picks for the previous year’s top studies in three research areas: equine medicine, reproduction, and surgery.

This year, Elizabeth Santschi, DVM, Dipl. ACVS, a professor of equine surgery at the Kansas State University College of Veterinary Medicine, in Manhattan, shared her top take-home messages for 2017 equine surgery-related studies during the convention, held Nov. 17-21 in San Antonio, Texas. This year’s presentation marked the end of her three-year term on the broadcast team.

Hock Injection Accuracy

In the first study Santschi recapped, researchers sought to determine how accurate veterinarians were at placing intra-articular (in the joint) injections in the two lower hock joints—the centrodistal (CD) and the tarsometatarsal (TMT)—in 12 healthy horses. Veterinarians injected 4 mL of contrast medium into each joint. The researchers noted needle repositioning and/or replacement, then took radiographs to determine where the medium was located within the desired joint.

The research team determined that:

  • Veterinarians successfully injected 23 of 24 TMT joints, for a success rate of 96%;
  • They were less successful at injecting CD joints, however, hitting the target in just 10 of 24 joints for a success rate of 42%;
  • There was communication (leakage) between the TMT and CD joints in 26% and 20% of successful TMT and CD injections, respectively; and
  • Years of experience did not appear to impact injection accuracy significantly.

Santschi said the leakage was likely due to the high injection volume (injections in the field often hover around 2 mL), but could impact withdrawal times in regulatory settings, such as when treating racehorses with intra-articular corticosteroids or non-steroidal anti-inflammatories in advance of a race.

Seabaugh KA, Selberg KT, Mueller POE, et al. Clinical study evaluating the accuracy of injecting the distal tarsal joints in the horse. Equine Vet J ISSN 0425-1644, DOI: 10.1111/evj.12667.

Comparing Emasculators for Castrations

The researchers behind the next study Santschi recapped compared two commonly used emasculators with different methods of action—the Serra and the Reimer—and how they impact equine castrations. The Reimer emasculator has a “double crush” action, meaning it first crushes the spermatic artery—which provides blood to the testicles—with one lever, then makes the final cut for testis removal with a second. The Serra crushes the artery and removes the testes in one shot.

The researchers tested the methods on two groups of 40 equine cadavers—one group using an open technique and the other using a closed technique. When an open castration is performed the parietal tunic (the sac or lining surrounding the testis) is incised, allowing direct access to the artery for crushing; with the closed technique, the parietal tunic is removed with the testis. Then, they further split the groups, castrating half using the Serra and half using the Reimer emasculators. Santschi said the researchers left the emasculators on for two minutes, then examined the testis and spermatic artery and measured testicular artery leaking pressure.

The team found few differences between the groups. Leaking pressure was higher (less likely to bleed after castration) in the open group with the Reimer, she said, and within the Reimer group, it was higher for open than closed castration.

But ultimately, Santschi said, “either emasculator works fine.”

Comino, F. Giusto G, Caramello V, et al. Do different characteristics of two emasculators make a difference in equine castration? Equine Vet J ISSN 0425-1644, DOI: 10.1111/evj.12713.

Navicular Bursotomy Outcomes

Horses with septic or contaminated navicular bursae typically face a long and uncertain road to recovery. Even with surgical intervention, their prognosis is typically guarded. So, in attempt to improve outcomes, a research team of veterinarians at Iowa State University College of Veterinary Medicine added regional limb perfusion (RLP) to the treatment equation. Santschi shared the results of their study of 19 horses that were at least lame at the walk.

Horses underwent a navicular bursotomy, in which the surgeon opened the bursa through the bottom of the hoof and lavaged the affected area with sterile fluid, in combination with RLP, which delivers high levels of drugs to leg tissues below a tourniquet, and systemic antimicrobials. Santschi said horses underwent two to three more RLP treatments and therapeutic shoeing at the surgeon’s discretion.

The good news, she said, is that all the horses survived. Sixteen returned to their previous use, and three became pasture-sound. The researchers reported that all 19 horse owners were satisfied with the outcome. They deduced that bursotomy in combination with systemic and local antimicrobials is an effective treatment for septic or contaminated navicular bursas.

Suarez-Fuentes DG, Caston, SS, Tatarniuk KD, et al. Outcome of horses undergoing navicular bursotomy for the treatment of contaminated or septic navicular bursitis: 19 cases (2002–2016). Equine Vet J ISSN 0425-1644, DOI: 10.1111/evj.12733.

Duration of Mepivacaine and Lidocaine Action in Nerve Blocks

Veterinarians perform palmar digital nerve blocks (PDNBs), which numb the rear portion of the hoof, for a variety of reasons. But regardless of why, PDNBs must last for an appropriate amount of time to allow practitioners to gather the information they’re seeking. Santschi shared the results of a study in which researchers compared the duration of action of two local anesthetics—mepivacaine and lidocaine—based on lameness resolution and skin sensitivity.

The scientists tested the medications on eight horses with induced forelimb lameness. They found that:

  • Mepivacaine resolved lameness in all eight horses;
  • Lidocaine resolved lameness in three horses;
  • Both drugs resulted in skin desensitization in all horses, but it happened sooner than lameness resolution after mepivacaine administration; and
  • Lameness resolution and skin sensitivity lasted longer with mepivacaine than lidocaine.

The researchers concluded that lidocaine isn’t ideal for PDNBs. In the study abstract, they said, “Mepivacaine is superior, with a reliable onset and longer duration of action,” but cautioned that “skin desensitization as an indicator for the onset of action or effectiveness of PDNBs for mepivacaine and lidocaine, or as a measure of the duration of action of lidocaine PDNBs should be interpreted with caution.”

Hoerdemann M, Smith, RL, Hosgood G. Duration of action of mepivacaine and lidocaine in equine palmar digital perineural blocks in an experimental lameness model. Vet Surg 2017, DOI.org/10.1111/vsu.12689.

Osteochondral Lesion Heritability and Prevalence

When potential buyers are perusing survey radiographs of yearlings they’re interested in purchasing at a sale, osteochondral lesions aren’t an uncommon finding. But just how common are these potential problems in Thoroughbreds, and are they hereditary? Santschi recapped a retrospective study in which researchers sought to find out.

The scientists reviewed 34 digital radiographs from each of 1,962 Thoroughbred yearlings in Australia. They identified osteochondral lesions and analyzed the horses’ pedigrees to estimate heritability. Santschi said some of their key findings included:

  • 23% of yearlings had at least one lesion;
  • Lesions were found in 10% of stifle joints, 8% of fetlock joints, and 6% of hock joints;
  • Overall heritability ranged from 0% to about 20%, with an average of 8%; and
  • Heritability was 16% for stifle lesions, 2% for fetlock lesions, and 0% for hock lesions.

Santschi cautioned that while this study revealed a “modest” genetic component, previous studies have shown a higher degree of hock lesion heritability. Because there is a tendency to label all orthopedic injuries in young horses as osteochondrosis and some are likely caused by trauma (acquired rather than inherited or developed because of conformation tendencies), she believes the veterinary community needs a better definition of osteochondral lesions.

Russell J, Matika O, Russell T, et al. Heritability and prevalence of selected osteochondrosis lesions in yearling Thoroughbred horses. Equine Vet J ISSN 0425-1644, DOI: 10.1111/evj.12613.

Subchondral Bone Cysts’ Impact on Local Bone Stresses

In the final study Santschi described, she and other research had examined how subchondral bone cysts (technically termed subchondral lucencies, or SCLs, a common finding in radiographs performed on horses being sold at public auction) in the stifle’s medial femoral condyle (MFC) impact local bone stresses. The researchers ran a CT scan on a yearling, then created a 3-D model in which they could “create” cysts (or voids) and “load” the joint to see how it reacts to different degrees of stress.

The team found significant differences in tension and shear stress (a stress state in which the structure’s shape deforms) at various stages of bone cyst development, which could lead to further bone damage and cyst enlargement.

“These data provide a first step in understanding of the altered mechanics of subchondral bone surrounding a SCL,” the team reported in the study abstract. “Additional studies may provide the basis for improved treatment strategies for SCL in young horses, and may improve the understanding of SCL in humans.”

Frazer LL, Santschi EM, Fischer KJ. The impact of subchondral bone cysts on local bone stresses in the medial femoral condyle of the equine stifle joint. Med Engineer and Physics 2017;48:158-167.