Making Great Strides

Photo courtesy of Animal Health Trust.

Sue Dyson, MA, VetMB, PhD, DEO, FRCVS, stands next to a towering near-black Warmblood gelding, preparing to administer nerve blocks to help pinpoint a hind-limb lameness. The diminutive veterinarian who heads the Animal Health Trust’s (AHT) Clinical Orthopaedics department, in Newmarket, United Kingdom, looks delicate beside the massive show jumper, but she’s a strong force in the world of equine orthopedic research. 

She watches the strapping show jumper trot up and work under tack while relaying her observations to the two veterinarian interns at her side. “What did you see when he trotted to the left?” Dyson asks one intern who hails from Greece. “Very good,” she says matter-of-factly upon hearing the woman’s response.

Dyson’s focus at the AHT is lameness and diagnostics, and her motto is this: “If you look carefully, you will always discover more conditions. You’re learning as you go along.”

Dyson has studied equine biomechanics alongside other AHT researchers for three decades, and she emphasizes that a lot has changed in that time—including the clinic itself. 

“When I first came here, the number of horses seen per week was tiny and the research output was small,” she said. “Now we’ve grown into purpose-built facilities with state-of-the-art equipment in all areas.”

The small but productive orthopedics team includes fellow researchers Rachel Murray, MA, VetMB, MS, PhD, MRCVS, Dipl. ACVS, ECVS, Annamaria Nagy, MedVet, FRCVS, and Marianna Biggi, DVM, PhD, MRCVS; research assistants Vicki Walker, MSc, and Carolyne Tranquille, BSc; veterinary pathologist Maria Jose Pinilla, DVM, MVetMed (path), MRCVS; and the two interns, who will complete published research projects during their time at the clinic. While Dyson’s department is just one of many within the AHT’s Centre for Equine Studies, it’s unique in that it functions as both a research platform and a working clinic.

“We have to combine money-earning with research,” she explains. “So we are involved in clinically related research. For instance, we do a lot of validation of imaging techniques versus pathology (disease or damage). If we have patients that don’t make it, we look at their tissues so we can correlate what we see on MRI with what’s actually present there in the body.”

In this article we will explore some of the areas Dyson and the orthopedic team are studying while simultaneously running this high-functioning equine clinic.

Saddle Slip

Dyson’s department made international waves last year when they discovered a correlation between lameness and saddle slip. 

“Everybody encounters horses in which the saddle slips, and everybody has historically suggested that (this slippage is caused by) the rider, the saddle, the saddler, or that the horse is asymmetrical,” Dyson explains. “Nobody has before mentioned lameness.”

She was inspired to investigate this cause after a client complained that her 6-year-old show jumper’s back felt like a plank when ridden. Dyson noted that the horse’s topline wasn’t as well-muscled as a professionally conditioned sport horse’s topline should be, and she wondered if it was a reflection of back pain or of problems elsewhere. Upon further examination she was surprised to find that the horse had good back flexibility.

“When I palpated the back I couldn’t find any foci of pain,” she recalls. “I started to think lameness was inducing back stiffness rather than primary back problems. Although I couldn’t see overt lameness, I started to nerve-block the hind limb on the side to which the saddle slipped. When I blocked the lower hock joint, the horse moved with much better swing through the back and the saddle slip resolved.”

Dyson recognized there could be something to this finding. From August 2011 to August 2012, she and PhD candidate Line Greve, DVM, MRCVS, assessed 128 horses presented at the AHT for lameness evaluation only and recorded both degree of lameness and saddle slip. They discovered that administering diagnostic anesthesia to hind-limb lame horses eliminated saddle slip in 97% of the cases. Based on this finding and others, they concluded that “saddle slip occurs in a high percent of the horses with hind-limb lameness, and saddle slip may actually be an indicator of subtle or low-grade hind-limb lameness.” Complete study results can be found at

Now Dyson and her team are in the process of surveying lameness and saddle slip in more than 500 sound sport horses in normal work, volunteered by their owners to participate in the study. 

“It appears that clinical and subclinical hind-limb lameness is a far more common cause of saddle slip in the general population than a poorly fitting saddle, asymmetry of the horse’s back, or rider crookedness,” she says. “Paradoxically, a well-fitting saddle is more likely to slip than an ill-fitting saddle, and lame horses with a round back shape are most at risk (for saddle slip).”

Arena Footing

Dyson is a proponent of sustainable equine athletic careers, and one aspect of this is using appropriate footing when riding. At the AHT she, Murray, Walker, and Tranquille have been studying how different arena surfaces and maintenance methods influence a horse’s movement.

They recently finished a study in which they investigated the effects of superficial harrowing a waxed sand and rubber surface and the effects of watering an unwaxed sand and fiber surface relative to mechanical surface characteristics and kinematics (measurement of body motion) of the working trot.

Based on their results and observations, the team concluded that superficial harrowing did not improve the waxed sand and rubber surface’s uniformity, possibly because the harrows were not going deep enough into the surface. As for the unwaxed sand and fiber surface, watering improved its uniformity. Their kinematic findings revealed:

  • An increase in forelimb and hind limb fetlock and hock extension when the elasticity of the arena surface decreased;
  • A decrease in joint flexion when the elasticity of the surface increased;
  • An increase in joint extension when surface firmness decreased; and 
  • A decrease in joint flexion when the firmness increased. 

All of these kinematic changes indicate the need for uniformity across an arena surface to prevent injury. Complete study results can be found at

Now researchers are exploring a link between arena surfaces and lameness in sport horses. Tranquille says that in previous studies the team observed that horses alter their gait when working on different surfaces and that—for dressage horses in particular—training on a variety of surface types was protective (in other words, if a horse learns to adjust to working on different surfaces, his risk of sustaining injury might be lower). However, little data exists on arena surface mechanical properties and how they potentially relate to equine injury. 

“We have recently assessed and compared the mechanical properties of three common surface types (waxed sand and fiber, unwaxed sand and fiber, and unwaxed sand and rubber), and the results showed there were significant differences in firmness, friction, and elasticity between all three surface types,” she explains.

In summary, she adds, each arena type poses pros and cons in regard to how the horse’s feet slide and how much he “bounces” off the surface. Surface quality and function also depend on proper arena maintenance, including leveling, harrowing, and watering.

MRI and Diagnostics

As MRI units become more widely available, researchers are learning more ways to diagnose injury using this rapidly advancing technology. The AHT orthopedic team is using MRI to not only validate their clinical findings but also pinpoint pathological changes in horses’ limbs that might predispose the animals to fractures or other injuries. For instance, they recently completed a collaborative study in which they examined a large number of racehorses that were injured and then -euthanized.

“We were able to look at 192 metacarpal (cannon) bones using MRI and 38 of these also with histopathology (looking at the tissue under a microscope) and compare the results,” Tranquille and Pinilla explain. “We found some novel changes within the structure of the bone and determined that the risk of fractures increases with increased mineralization in the palmar aspect (back) of the condyles of the cannon bone.”

Dyson and Nagy previously used MRI and histology to describe the normal anatomy of the soft tissues of the palmar aspect of the carpus (knee). “Two similar projects are under way (at the AHT) to describe the normal anatomy of the soft tissues of the plantar aspect (bottom) of the hock and the complex anatomy of the upper hock joints,” Tranquille says.

She adds that they will also evaluate the suspensory ligament (which originates at the top back of the cannon bone, continues down to the fetlock region, and attaches to the top of the proximal, or upper, sesamoid bones)—a structure that sport horses injure frequently.

“Understanding the normal anatomy of structures will allow us to correlate their (healthy) appearance with their (injured) appearance on different diagnostic imaging techniques,” Tranquille explains. 

We see a phenomenal incidence of proximal suspensory desmitis in young potential dressage horses sold through high performance sales. The question is why.

Dr. Sue Dyson


In ongoing studies, members of the orthopedics department are examining how different gaits induce different degrees of limb flexion and extension and how those mechanics might influence suspensory apparatus (the suspensory ligament and its surrounding structures that all function to prevent fetlock hyperextension) loading. The team hopes to learn more about methods that might help prevent suspensory ligament injuries, particularly in hind limbs.

“We very much try to address applied problems,” Dyson notes. “For example, we see a phenomenal incidence of -proximal suspensory desmitis in young potential dressage horses sold through high--performance sales. The question is why. Are these horses being asked to do too much too soon? They’re being shown in these very extravagant paces.” 

Walker and Murray revealed in a recent study that the horses experience greater sinking of the fetlocks in extension than in collection. They determined, therefore, that extension can be more detrimental to the suspensory apparatus than collection, particularly in the immature horse.  

Because dressage horses generally are at higher risk for sustaining suspensory ligament injury than other sport horses (a trend Murray showed in 2006), the research team has also recently begun an all-encompassing investigation of the mechanisms of suspensory ligament injury development and ways to prevent it.  

“Analysis is ongoing, but initial findings suggest that horses performing lengthened paces on firm, high-traction surfaces may place increased strain on the suspensory ligament,” Murray notes. 

The Pessoa Training Aid

In one of Walker’s main studies, she’s focusing on the Pessoa Training Aid’s effects on sport horse performance and rehabilitation. Developing core muscle strength is important both for performance and injury rehabilitation in sport horses, and the Pessoa Training Aid is marketed to strengthen the back, engage the hindquarters, stretch the topline, and encourage a horse to use his body correctly. But despite its widespread use within the equine industry, Walker says there is limited information about its true effect on horses’ kinematics. 

“We have carried out a study to determine the effect of the Pessoa Training Aid on the temporal, linear, and angular kinematics of the working trot,” she says. “The findings suggest that a Pessoa Training Aid may be beneficial for general training and rehabilitation as a method of improving posture, stimulating core muscle activation, and improving overall way of going, without increasing the loading of forelimb and hind limb structures.”

Oral Joint Supplements

Another ever-popular research focus that the AHT orthopedics team has adopted is oral joint supplement efficacy.

Tranquille described a recent study (blinded, with controls) they have been involved in that aims to determine one joint health product’s effect on orthopedic, physiotherapy, and handler evaluation in 24 mature horses (age 4 to 12) that scored less than two on a 1-5 lameness scale. This product, produced by Purina (FreedomFlex) is comprised of chondroitin sulphate, glucosamine, vitamin C, methyl sulphonyl methane, and omega fatty acids docosahexaenoic acid and eicosapentaenoic acid.

“The results showed that oral administration of this supplement was associated with improved lameness scores, optimal ridden/groundwork scores, and improved ‘ease-of-movement’ in the field,” Tranquille says.

Take-Home Message

With a seemingly never-ending supply of sport horse lameness cases trotting through its clinic doors, it’s no wonder the AHT orthopedics department is also a cutting-edge research center. Patient patterns and pathologies aid Dyson and the rest of the team in putting hard science behind observations, ultimately improving worldwide understanding of normal equine anatomy and function. 

About the Author

Alexandra Beckstett, The Horse Managing Editor

Alexandra Beckstett, Managing Editor of The Horse and a native of Houston, Texas, is a lifelong horse owner who has shown successfully on the national hunter/jumper circuit and dabbled in hunter breeding. After graduating from Duke University, she joined Blood-Horse Publications as Assistant Editor of its book division, Eclipse Press, before joining The Horse.

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