Tendon function and failure: Recent advances

Published in European Trainer - October - December 2017, issue 59

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Tendon injuries continue to be one of the most problematic injuries that affect racehorses. One of major issues facing veterinarians and trainers is that we have little understanding of why tendons become injured in the first place, how such the SDFT in the horse acts like the spring of a pogo stick, stretching and storing energy as a horse lands, and releasing energy to aid a horse’s locomotion as the limb pushes off.

There is a lot of clinical and research focus on these “energy-storing” tendons (such as the equine SDFT), as it is these tendons which are most prone to injury, and it appears to be a property of the function of such high strain, elastic tendons which result in these significant injuries will lead to so much economic loss and welfare issues for the affected horses. Under such extreme mechanical demands, it is not surprising the SDFT is prone to overuse injury, particularly amongst racehorses. SDFT injuries are highly debilitating, requiring considerable rehabilitation periods and are often career-limiting.

There is little convincing evidence of efficacy for any current treatment, and even after extensive periods of rest and rehabilitation, re-injury rates are extremely high, with little knowledge of how best to safely reintroduce training.  In the horse, tendons are also extremely long, due to the length of a horse’s leg. In the horse’s forelimb, there is no muscle lower in the leg than the level of the knee (carpal) joints, and tendons mainly extend from the level of the knee down to the hoof.

To understand why tendons, such as the equine SDFT, become injured and how we may develop methods to allow better treatments, we and other researchers, have been developing an understanding of how elastic “energy-storing” tendons function and how do they fail.

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Musculoskeletal injuries - impact and prediction

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Synovial Infections

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Byerley Technologies launch Tendon Manager

Byerley Technologies has combined the knowledge of the horse industry with experts in data management systems to develop Tendon Manager, an automatic system that allows for the  Early detection of potential lower leg injuries.

Tendon Manager is a world first in the management of equine lower leg health and delivers a simple user-friendly end solution to the equine sector.  .

Key Early Detection benefits include:  reassurance for trainers and owners; economic benefit for both trainer and owner and improved welfare. The system is fast, non-invasive, accurate and easy to interpret.

Byerley Technologies will be launching Tendon Manager this April at DBS, Doncaster Breeze up Sales, on 22nd and 23rd April.

OMBISTEM-Vet stem cell treatment from Vetbiobank

Whether it be an Olympic track gold medallist or a Derby winner, all athletes, will inevitably suffer injuries to ligaments, joints and tendons. This goes with the territory. Every trainer, be it human or equine, hopes to restore his charge quickly to full competitive glory both legally and economically.

Regenerative medicine has been in force in human clinics and the vet’s practice for over a decade using products such as platelet rich plasma (PRP) or stem cells. However, over the last few years the use and type of stem cells has changed dramatically.

Historically, stem cells were obtained from the fat or bone marrow of the horse to be treated and then injected as a crude product into the injured site immediately or after a 2-3 week delay needed to produce sufficient cells. Detrimentally, cell potential decreased with the time lag during production and treatment was done usually when fibrosis was already manifest.

Vetbiobank’s treatment options are based on having a bank of ready-to-use neonatal stem cells obtained from the umbilical cord that can be administered well before fibrotic onset.

Vetbiobank’s, OMBISTEM-Vet system offers advantages over traditional stem cells products. The cells are fitter and more standardised and less subject to the vagaries of adult cells whose therapeutic potential decreases with age. Their gestational origin means those cells are less immunogenic, thus allowing treatment of both related and unrelated horses. 

Stem cells implanted in a clinically manifest lesion will also migrate to other injured sites which means they preserve health by repairing other undetected lesions. (European trainer magazine June 2014).

This development has attracted widespread interest within the racing community. Furthermore, cord collection can be performed easily in any hygienic stable. Therefore, a stud farm can build with Vetbiobank, a cell bank to treat a lifetime of common horse injuries. 

For a racing stable, without its own bank, it is still possible to access cord stem cells from Vetbiobank’s OMBISTEM-Vet product to treat injuries.

Vetbiobank’s expertise in neonatal stem cell banking and research enables them to offer a BESPOKE pan European cell therapy service to vets, trainers, breeders and horse owners.

Visit www.vetbiobank.com for more information.

HBLB tendon & ligament research - equine injury prevention and management

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Thermography

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Tendon Treatments - how to treat the common injury

Tendon damage is one of the most common and perplexing soft tissue injuries in racing jurisdictions throughout the world. Roughly eight to thirty percent of racehorses in the United States, eleven percent in Japan, five to fifty percent in the United Kingdom (including jump horses) and at least five percent in Australia sustain tendon injuries during their careers.

Kimberly French
 (20 January 2009 - Issue Number: 11)

Pelvic asymmetry in racehorses - increased risk of injury?

By Nicole Rossa

Steeplechase racing in particular is a high risk sport for the horse. There is currently some fairly extensive research into racehorse injuries and fatalities on the racecourse, with previously published scientific reports on the subject being widely available. The racing industry is aware of the need for such reports, as the industry itself is very much in the public eye with regard to injury rates on the racecourse. 

Lameness is one of the main reasons for wastage in the racehorse industry, and was the reported cause of 68% of total horse days lost to training in a study of racehorses in England (Rossdale et al. 1985). This study also suggested that 10% of all diagnosed lameness cases were caused by tendon injury.  Overstrain injuries to the superficial digital flexor tendon (SDFT) are amongst the most common injuries observed in the athletic horse (Goodship, 1993).  It is therefore important to determine all possible causative factors of SDFT injury so that methods for preventing injury can be implemented as part of a training programme.

Hindquarter Asymmetry


The hindquarters of the horse provide the propulsion, and the forelimbs support 60% of the horse's weight.  Problems affecting the pelvic structure in the horse can lead not only to poor performance, but also to an unlevel gait and to lameness of the hindlimb.  There are to date very few scientific reports on the frequency of hindquarter asymmetries in the horse, although Bathe (2002) found that most hard working horses were likely to have some degree of pelvic asymmetry.   This factor may not always affect performance, as many successful horses have been found to have asymmetry of the pelvis.

Dalin et al. (1985) investigated the hindquarter asymmetry in Standardbred Trotters for any correlation with poor performance. He measured differences in height between the left and right tuber sacrale when the horse was standing square.  Of the 500 horses measured 39 of them showed marked hindquarter asymmetry.  In 30 horses the tuber sacrale was lower on the left, and in 9 horses it was lower on the right.  The asymmetric horses had significantly inferior performance (measured by total earnings) compared to the symmetrical horses.  All the horses were trained and raced in Sweden on a left handed track. The asymmetrical horses were also of significantly larger body size than the symmetrical horses.

In a recent study undertaken by Stubbs et al. (2006) in conjunction with the Hong Kong Jockey Club, a number of racehorses were presented for euthanasia (for injury and/or lameness).  Racing and training details were examined in detail, and a clinical examination was carried out before the horses were euthanased. Following post mortem the thoracolumbar spine and pelvis were dissected out and examined.  Although not part of the study it was noted that asymmetry of the pelvis was prevalent in many of the horses that had been dissected, the reason probably being due to a natural torsion of the pelvis as a result of training and racing on right handed tracks only.

It is suggested that asymmetrical loads on the pelvic structure caused by external factors (such as racetrack), and by internal factors (such as locomotor apparatus pain) may lead to a higher stress being placed on one hindlimb, and as a result lead to the development of pelvic asymmetry which may be apparent as pelvic rotation.  Improper movement patterns of the hindquarters, due to pain caused by overuse or from fatigue, may also result in abnormal alignment of the pelvic structure.  This in turn may then cause overloading on the forelimbs (by off loading the hindquarters) and therefore predisposing the forelimbs to injury.  If this can be proved then surely this would emphasise the importance of correcting pelvic misalignments using manipulation techniques such as chiropractic, osteopathic and myofascial release approaches.  There is some unpublished material available to support the use of McTimoney manipulation methods and other soft tissue manipulation in the correction of pelvic rotation.

Hindquarter asymmetry is often associated with sacroiliac joint lesions or with chronic hindlimb lameness.  The tuber sacrale can appear asymmetrical in clinically normal horses as well as in horses with misalignment of the sacroiliac joint (Dyson, 2004). Horses with longstanding poor performance attributed to chronic sacroiliac damage were investigated by Jeffcott et al. (1985).  The majority of these horses showed some asymmetry of the hindquarters with the tuber coxae and tuber sacrale lower on the same side that the animal was lame on. Hindquarter asymmetry may be due to some tilting or rotation of the pelvis in addition to muscle wastage of one quarter, usually the side the horse is lame on.

Abnormal Alignment 
of the Pelvis


Pelvic rotation or abnormal alignment of the pelvis to the thoracolumbar spine can be measured by the level of the tuber coxae to the ground.  If the horse is unable to produce the propulsion from its hindquarters due to discomfort in the pelvic region, then the forelimbs may be required to provide more horizontal propulsion.  The horse will in effect be pulling himself forward with his forelimbs, rather than pushing from his hindquarters.  This may result in over development of the shoulder muscles, thereby reducing the efficiency of the forelimb movement by adding unnecessary weight.

Unpublished data has suggested a positive relationship between injury to the forelimb stay apparatus and pelvic asymmetry, particularly where the presence of functional asymmetry in the hindquarters was found to be due to pelvic rotation, and not as a result of differences in individual bone lengths of the hindlimb.

Lameness and Compensatory Movement Patterns


The compensatory mechanisms of horses with lameness have been extensively researched and reported.  The potential for secondary injuries resulting from a horse's attempt to compensate for lameness by altering its gait pattern are still unclear.  Clayton (2001) found that when a lame limb is supporting body weight, the horse minimises pain by decreasing the load on that limb, resulting in a compensatory increase in the vertical forces in other limbs.  The compensating limbs are therefore subjected to abnormally high forces, and these may lead to lameness in the compensating limbs.

Uhlir et al. (1997) found that in all cases of diagnosed hindlimb lameness that true lameness of the left hind caused a compensatory lameness of the left fore, and that true stance phase lameness of the left fore caused a compensatory lameness in the right hind.

Tendon Injury
The SDFT is the most frequently injured tendon in horses. 

 In a recent study of steeplechase horses diagnosed with tendon and ligament injuries sustained during training, 89% occurred in the SDFT (Ely et al. 2005).  It has been suggested that an optimum level of exercise is required at an early age for tendon adaptation to training, but with increasing age accumulation of microdamage and localised fatigue, failure to the tendon will occur with increasing exercise (Smith et al. 1999).

The induction of injury to the SDFT occurs when loading overcomes the resistive strength of the tendon. Factors which increase the peak loading of the SDFT, such as weight of rider, ground surface, shoeing, conformation, incoordination, jumping, and speed will act not only to increase the rate of degeneration, but will also increase the risk of the onset of SDFT strain (Smith, 2006).  Therefore the prevention of tendon strain-induced injuries by reducing some of the risk factors that increase loading on the tendon may provide the most satisfactory answer.
Animal Manipulation Techniques
McTimoney Animal Manipulation aims to improve asymmetries through manipulation.  There has been much anecdotal evidence for the benefits of McTimoney Manipulation Techniques on animals (Andrews and Courtney, 1999).  There is anecdotal evidence to suggest that McTimoney and other manipulative therapies can make a difference where veterinary medication has failed (Green, 2006), although the application of manipulation techniques in veterinary medicine may be dependent of further research into the clinical effects of manipulation.

Manipulation techniques are thought to cause muscle relaxation and to correct abnormal motor patterns which may be the result of muscular imbalances and restricted joint motion or altered joint mobility (Haussler, 1999).  There is some unpublished material to support that there are significant changes in the symmetry of the pelvis after the application of McTimoney manipulation techniques, and that there is continued improvement one month after initial treatment.

Current Research into Pelvic Alignment


In a recent unpublished study a group of 40 steeplechase horses in training, all using the same gallop, were measured for pelvic asymmetry. The measurement technique used was a somewhat simple (but reliable) method.  Each horse was measured on flat, level concrete while standing completely square and weight bearing on all four limbs.  Measurements were taken vertically using a horse measuring stick with a spirit level, from the most dorsal aspect of the lateral wing on the ilium (the tuber coxae) to the ground, on the left and right sides.
Various data was collected on each horse, regarding race history, how many races run, whether "bumper" (flat races for steeplechase bred horses), hurdle or steeplechase, prize money earnings, handicap rating, and also brief veterinary history.

The aim of the study was to compare pelvic rotation in 20 sound horses to the incidence and degree of pelvic rotation in a group of 20 horses with SDFT strain in either one or both forelimbs. Both the sound horses and the injured horses were in training with the same trainer, and therefore had used the same gallops, and underwent the same training regime.

Although no significant difference was found in the number of horses with pelvic rotation in sound horses compared with the number of horses with tendon strain, there was a high incidence of pelvic rotation in the group as a whole, with a predominance towards pelvic rotation on the right. This could have been due to training methods or gallops used, and certainly warrants further research.

There was no significant association between side of pelvic rotation and side of forelimb tendon strain, but again warrants further investigation using a larger number of horses.  Due to the prevalence of right side pelvic rotation it would not have been possible to show any significant associations anyway between left and right forelimb injury.

The study did present some trends for age of horse, sex, and race history; showing that the number of horses with pelvic rotation and tendon injury increased with age.  Geldings tended towards a higher incidence of tendon injury, and mares tended towards a higher incidence of pelvic rotation. There were equal numbers of sound and injured horses for each race type, but the degree of pelvic rotation in horses that had fallen was notably larger than in the horses that had not fallen.

Future Studies into Pelvic Asymmetry


The preliminary investigation as described above has formed the basis for further research into abnormal pelvic alignment in racehorses, and whether or not there is any association between side of misalignment and side of forelimb injury.  Further research is due to be carried out with a larger sample of horses, and from different yards, to investigate whether there is any prevalence as to the side of misalignment, or if pelvic alignment is affected by training methods and the use of different gallops and that there is continued improvement one month after initial treatment.

Current Research into Pelvic Alignment


In a recent unpublished study a group of 40 steeplechase horses in training, all using the same gallop, were measured for pelvic asymmetry. The measurement technique used was a somewhat simple (but reliable) method.  Each horse was measured on flat, level concrete while standing completely square and weight bearing on all four limbs.  Measurements were taken vertically using a horse measuring stick with a spirit level, from the most dorsal aspect of the lateral wing on the ilium (the tuber coxae) to the ground, on the left and right sides. Various data was collected on each horse, regarding race history, how many races run, whether "bumper" (flat races for steeplechase bred horses), hurdle or steeplechase, prize money earnings, handicap rating, and also brief veterinary history. The aim of the study was to compare pelvic rotation in 20 sound horses to the incidence and degree of pelvic rotation in a group of 20 horses with SDFT strain in either one or both forelimbs. Both the sound horses and the injured horses were in training with the same trainer, and therefore had used the same gallops, and underwent the same training regime.
Although no significant difference was found in the number of horses with pelvic rotation in sound horses compared with the number of horses with tendon strain, there was a high incidence of pelvic rotation in the group as a whole, with a predominance towards pelvic rotation on the right. This could have been due to training methods or gallops used, and certainly warrants further research.

There was no significant association between side of pelvic rotation and side of forelimb tendon strain, but again warrants further investigation using a larger number of horses.  Due to the prevalence of right side pelvic rotation it would not have been possible to show any significant associations anyway between left and right forelimb injury.

The study did present some trends for age of horse, sex, and race history; showing that the number of horses with pelvic rotation and tendon injury increased with age.  Geldings tended towards a higher incidence of tendon injury, and mares tended towards a higher incidence of pelvic rotation. There were equal numbers of sound and injured horses for each race type, but the degree of pelvic rotation in horses that had fallen was notably larger than in the horses that had not fallen.

Strengthening Young Thoroughbreds' Limbs

One of the major challenges in training racehorses is keeping them sound. Not unlike a human athlete, a racehorse's ligaments, tendons, bones and joints are susceptible to injury throughout its career and, at times, it seems impossible to avoid some sort of musculoskeletal mishap.

A vast number of components can comprise any musculoskeletal injury but many believe the economics of the Thoroughbred industry - namely the preparation of young horses for 2-year-old sales and racing 2-year-olds - are the main culprits for these sorts of injuries.
Training for most race horses commences when they are 18 to 20 months old. The skeleton of a horse often does not reach full maturity until they are four years old so training at a young age might predispose horses to a multitude of career-limiting or -ending injuries.
Shin soreness or bucked shins is an extremely common condition in young racing Thoroughbreds and Quarter Horses (and occasionally Standardbreds.) It involves the front portion of the cannon or metacarpal bone and is the result of rapid bone modeling.
Before a horse begins training, its cannon bones have the same thickness all the way around. When horses start galloping, there is a considerable increase in stress on the front of the cannon bone.  To contend with the stress, the equine body responds by adding new bone to the area in duress. Ultimately, this creates stronger bones but early on this new bone is prone to microfractures similar to the stress fractures that human athletes endure during training.
The severity of bucked shins can vary greatly, but most horses will exhibit pain when the cannon bone area is massaged, will be lame while trotting, and have a short, choppy stride. Another symptom is swelling in this area of the leg.
The condition is usually diagnosed by recognizing the clinical indicators in a horse when it begins its first training and/or racing campaign. Horses suffering from shin soreness must be rested until all signs of lameness have disappeared, which can take several days or many months.
For example, New York-based trainer Barclay Tagg's then 2-year-old colt, Tale of Ekati, had sore shins and returned after a month of light training to triumph in the Grade 2, $250,000 Belmont Futurity on September 15th of last year.
"One shin was very sore, but he got over it very quickly," Tagg said. "I got two real good works into him."
While Maimonides, a 2-year-old, owned by Ahmed Zayat, exited the Grade 1 Hopeful Stakes held at Saratoga Race Course on September 3 with the same affliction, his recovery was expected to take a bit longer. Sonny Sonbol, Zayat's racing manager, said he needed "three to four weeks to get over his shins and start back training and get ready for the winter."
Estimates vary, but it is believed between 65 and 90 percent of all Thoroughbreds in the United States and more than 40 percent of all Thoroughbreds in Australia buck their shins early in training.
About only 12 percent of young English racehorses buck their shins. Unlike the United States and Australia, much less emphasis is placed on 2-year-old racing in England and English horses are trained on straight tracks, so less strain would be placed on the cannon bone.
However, the English are not immune to their young horses being injured. In a study of 314 young Thoroughbreds in Newmarket more than 50 percent experienced some period of lameness, and in roughly 20 percent of those horses, the lameness prevented them from racing.
Also, bucked shins are not exclusively relegated to 2-year-olds but to all horses which are just beginning intense training. Some horses can suffer recurrences of shin soreness after a period of stall of paddock rest. Therefore, bucked shins do not discriminate based on the age of a horse, but depend on how intense the training is and if the horse is undertaking the action for the first time.
Dr. David Nunamaker, VMD, PhD, is an orthopedic surgeon and chair of the research department at the University of Pennsylvania's New Bolton Center who had conducted extensive research on bone development from 1982 to the present. Dr. Nunamaker, Dr. William Moyer, DVM, chair of the Large Animal and Surgery Department at Texas A&M University and Dr. John Fisher, DVM, an equine veterinarian and Maryland horse trainer, analyzed their research results and established a training system created to reduce the severity of bucked shins or erase them.
"We found that a horse's bone shape alters in response to its training," Dr. Nunamaker said. "The way most conventional training is conducted, a bone changes in a way it should not and that is why you get into trouble with bucked shins. Also saucer fractures seem to occur only in horses that have previously bucked their shins. This could lead to catastrophic fracture."
Dr. Nunamaker concluded a problem will become evident after 50,000 cycles of trotting and galloping. A cycle is equal to one swift stride.
"The Standardbred doesn't have issues with bucked shins because you never see a pacer do anything but pace while Thoroughbreds train with a variety of gaits, such as walking, trotting and galloping," Dr. Nunamaker said. "Thoroughbreds do not run while they are training and when they do run it's only every 10 to 14 days. The bone remodels to what it experiences - which is not racing."
Speed work is very important because when a horse runs at speed, the angle of strain is much greater. So horses that breeze more often remodel their bones for racing.
Utilizing the research results, Dr. John Fisher adheres to a training program that stresses and stimulates the cannon gradually.
"When a horse is breezed, the bone sees it as an emergency and immediately begins laying down new bone," Dr. Fisher said. "This new bone is weak and needs to be strengthened through later remodeling, which would be triggered by further breezes spaced closer together. If remodeling is not allowed to take place and the horse is asked to do too much before he is ready, the new bone will be weak and prone to injury. The bone-strengthening is entirely based on stress and recovery to gradually increase bone density and strength."
In Dr. Fisher's program, horses transition from a one furlong work at 15 seconds to a half-mile or more in 13 seconds over a 16-week period.
If there are more than four days between short distance works, Drs. Nunamaker and Fisher have discovered the new bone will stop rebuilding and actually weaken, with no additional stress after five days.
Once the program has been finished, a horse is prepared to begin conventional training because he should have accumulated enough bone strength that he will not buck shins. However, if a horse is subjected to different track conditions or circumferences, such as a European horse racing on American dirt, the threat of shin soreness resurfaces.
Even though Dr. Fisher has modified the program throughout the years, he is still quite pleased with its performance.
"We just don't have many injuries at all," Dr Fisher said. "No more tendons, no more suspensories, no more fractures."
How much high-speed work and distance are required to signal the bone to remodel itself correctly and not form weaker bone? Research is still being conducted but Dr. Nunamaker claims the goal is to correctly change the bone at the slowest possible speed over the shortest possible distance.
 
"Maybe two furlongs, maybe one furlong," Dr. Nunamaker said. "Maybe it won't even have to be that far. We just don't know but there is a fine line during a crucial time period as to what is too much and what is not enough."
Once the bone has attained maximum strength by becoming thicker at its stress points, it should stay that way.
"When we looked at the timing of the injuries that occurred in horses that have shin injuries, we found that when the horse reached four years old, it no longer had shin injuries," Dr. Nunamaker said. "It may develop injuries to other parts of its body, but not to the shins. It is in the first two years of its training program, if it starts at two years of age, that it is going to have shin injury problems. After that no more shin injuries."
It is important to note the bones are the slowest part of the body to train. In most cases, the cardiovascular system and soft tissues are prepared for the stress of racing before the bones.
Study results presented at the 2005 Australian Veterinary Association depict shin soreness or bucked shins can be avoided. Certain training techniques place horses at risk for this condition.
The most significant factor was how far the horse trained and how quickly he went. If a horse trained at a speed greater than 33 mph during its first ten weeks of training, he tended to have some shin pain.
"A gradual increase in the weekly distances at these speeds is the key to reducing the number of cases," Dr. David Evans, BVSc, PhD and associate professor of veterinary science at the University of Sydney and one of the researchers on the project, said.
The study also revealed that using short gallops of 200-300 meters at 33 mph or greater can decrease shin soreness; training horses to induce shin soreness will not reduce the risk of contracting the condition during subsequent training; and shin pain occurred much less often in horses that began training at an average age of 30 months.
Dr. Evans acknowledged that much more research was necessary before any authoritative program could be implemented.
K.L.P. Verheyen, DVM, MSc, PhD, MRCVS, of the Royal Veterinary College (RVC) in London, agrees with Drs. Nunamaker and Evans that training methods are associated with injury risk.
"Stress injuries are repetitive loading injuries," Dr. Verheyen said. "Compare it to a paper clip and if you keep bending it, it will break. Interval training (alternate periods of hard exertion and rest) is a better option because high-speed exercise is as not bad as previously thought. It actually stimulates bone to respond, because bone is a living tissue and is constantly remodeling. If the same exercise is repeated again and again, the bone will stop responding, which is what we think is happening with the low-speed exercise and stress fractures."
While more research must be conducted to provide greater insight into how equine bones adapt and grow, even less is known about how tendons and ligaments respond to training. In a series of recent studies, Allan Goodrich, a professor at the Royal Veterinary College and the University College of London, discovered that the tendons of young horses (less than two years) strengthen in response to training. These results raise the possibility that early training enhances the development of the limb's support structures and could diminish injuries during training and racing.
After reviewing training methods and treatments, it is obvious much more research must be completed before any sound strength management program can be introduced.
"We just don't have all the answers yet," Dr. Nunamaker said.

Kimberly French 
(14 February 2008 - Issue 7)

Current research on Pelvic Asymmetry in Racehorses

Steeplechase racing in particular is a high risk sport for the horse. There is currently some fairly extensive research into racehorse injuries and fatalities on the racecourse, with previously published scientific reports on the subject being widely available. The racing industry is aware of the need for such reports, as the industry itself is very much in the public eye with regard to injury rates on the racecourse. Lameness is one of the main reasons for wastage in the racehorse industry, and was the reported cause of 68% of total horse days lost to training in a study of racehorses in England (Rossdale et al. 1985).

This study also suggested that 10% of all diagnosed lameness cases were caused by tendon injury. Overstrain injuries to the superficial digital flexor tendon (SDFT) are amongst the most common injuries observed in the athletic horse (Goodship, 1993). It is therefore important to determine all possible causative factors of SDFT injury so that methods for preventing injury can be implemented as part of a training programme.

HINDQUARTER ASYMMETRY

The hindquarters of the horse provide the propulsion, and the forelimbs support 60% of the horse’s weight. Problems affecting the pelvic structure in the horse can lead not only to poor performance, but also to an unlevel gait and to lameness of the hindlimb. There are to date very few scientific reports on the frequency of hindquarter asymmetries in the horse, although Bathe (2002) found that most hard working horses were likely to have some degree of pelvic asymmetry.

This factor may not always affect performance, as many successful horses have been found to have asymmetry of the pelvis. Dalin et al. (1985) investigated the hindquarter asymmetry in Standardbred Trotters for any correlation with poor performance. He measured differences in height between the left and right tuber sacrale when the horse was standing square. Of the 500 horses measured 39 of them showed marked hindquarter asymmetry. In 30 horses the tuber sacrale was lower on the left, and in 9 horses it was lower on the right. The asymmetric horses had significantly inferior performance (measured by total earnings) compared to the symmetrical horses.

All the horses were trained and raced in Sweden on a left handed track. The asymmetrical horses were also of significantly larger body size than the symmetrical horses. In a recent study undertaken by Stubbs et al. (2006) in conjunction with the Hong Kong Jockey Club, a number of racehorses were presented for euthanasia (for injury and/or lameness). Racing and training details were examined in detail, and a clinical examination was carried out before the horses were euthanased. Following post mortem the thoracolumbar spine and pelvis were dissected out and examined. Although not part of the study it was noted that asymmetry of the pelvis was prevalent in many of the horses that had been dissected, the reason probably being due to a natural torsion of the pelvis as a result of training and racing on right handed tracks only.

It is suggested that asymmetrical loads on the pelvic structure caused by external factors (such as racetrack), and by internal factors (such as locomotor apparatus pain) may lead to a higher stress being placed on one hindlimb, and as a result lead to the development of pelvic asymmetry which may be apparent as pelvic rotation. Improper movement patterns of the hindquarters, due to pain caused by overuse or from fatigue, may also result in abnormal alignment of the pelvic structure.

This in turn may then cause overloading on the forelimbs (by off loading the hindquarters) and therefore predisposing the forelimbs to injury. If this can be proved then surely this would emphasise the importance of correcting pelvic misalignments using manipulation techniques such as chiropractic, osteopathic and myofascial release approaches. There is some unpublished material available to support the use of McTimoney manipulation methods and other soft tissue manipulation in the correction of pelvic rotation. Hindquarter asymmetry is often associated with sacroiliac joint lesions or with chronic hindlimb lameness.

The tuber sacrale can appear asymmetrical in clinically normal horses as well as in horses with misalignment of the sacroiliac joint (Dyson, 2004). Horses with longstanding poor performance attributed to chronic sacroiliac damage were investigated by Jeffcott et al. (1985). The majority of these horses showed some asymmetry of the hindquarters with the tuber coxae and tuber sacrale lower on the same side that the animal was lame on. Hindquarter asymmetry may be due to some tilting or rotation of the pelvis in addition to muscle wastage of one quarter, usually the side the horse is lame on.

ABNORMAL ALIGNMENT OF THE PELVIS

Pelvic rotation or abnormal alignment of the pelvis to the thoracolumbar spine can be measured by the level of the tuber coxae to the ground. If the horse is unable to produce the propulsion from its hindquarters due to discomfort in the pelvic region, then the forelimbs may be required to provide more horizontal propulsion. The horse will in effect be pulling himself forward with his forelimbs, rather than pushing from his hindquarters. This may result in over development of the shoulder muscles, thereby reducing the efficiency of the forelimb movement by adding unnecessary weight. Unpublished data has suggested a positive relationship between injury to the forelimb stay apparatus and pelvic asymmetry, particularly where the presence of functional asymmetry in the hindquarters was found to be due to pelvic rotation, and not as a result of differences in individual bone lengths of the hindlimb.

LAMENESS AND COMPENSATORY MOVEMENT PATTERNS

The compensatory mechanisms of horses with lameness have been extensively researched and reported. The potential for secondary injuries resulting from a horse’s attempt to compensate for lameness by altering its gait pattern are still unclear. Clayton (2001) found that when a lame limb is supporting body weight, the horse minimises pain by decreasing the load on that limb, resulting in a compensatory increase in the vertical forces in other limbs. The compensating limbs are therefore subjected to abnormally high forces, and these may lead to lameness in the compensating limbs. Uhlir et al. (1997) found that in all cases of diagnosed hindlimb lameness that true lameness of the left hind caused a compensatory lameness of the left fore, and that true stance phase lameness of the left fore caused a compensatory lameness in the right hind. TENDON INJURY The SDFT is the most frequently injured tendon in horses. In a recent study of steeplechase horses diagnosed with tendon and ligament injuries sustained during training, 89% occurred in the SDFT (Ely et al. 2005). It has been suggested that an optimum level of exercise is required at an early age for tendon adaptation to training, but with increasing age accumulation of microdamage and localised fatigue, failure to the tendon will occur with increasing exercise (Smith et al. 1999). The induction of injury to the SDFT occurs when loading overcomes the resistive strength of the tendon. Factors which increase the peak loading of the SDFT, such as weight of rider, ground surface, shoeing, conformation, incoordination, jumping, and speed will act not only to increase the rate of degeneration, but will also increase the risk of the onset of SDFT strain (Smith, 2006). Therefore the prevention of tendon strain-induced injuries by reducing some of the risk factors that increase loading on the tendon may provide the most satisfactory answer.

ANIMAL MANIPULATION TECHNIQUES

McTimoney Animal Manipulation aims to improve asymmetries through manipulation. There has been much anecdotal evidence for the benefits of McTimoney Manipulation Techniques on animals (Andrews and Courtney, 1999). There is anecdotal evidence to suggest that McTimoney and other manipulative therapies can make a difference where veterinary medication has failed (Green, 2006), although the application of manipulation techniques in veterinary medicine may be dependent of further research into the clinical effects of manipulation. Manipulation techniques are thought to cause muscle relaxation and to correct abnormal motor patterns which may be the result of muscular imbalances and restricted joint motion or altered joint mobility (Haussler, 1999). There is some unpublished material to support that there are significant changes in the symmetry of the pelvis after the application of McTimoney manipulation techniques, and that there is continued improvement one month after initial treatment.

CURRENT RESEARCH INTO PELVIC ALIGNMENT

In a recent unpublished study a group of 40 steeplechase horses in training, all using the same gallop, were measured for pelvic asymmetry. The measurement technique used was a somewhat simple (but reliable) method. Each horse was measured on flat, level concrete while standing completely square and weight bearing on all four limbs. Measurements were taken vertically using a horse measuring stick with a spirit level, from the most dorsal aspect of the lateral wing on the ilium (the tuber coxae) to the ground, on the left and right sides. Various data was collected on each horse, regarding race history, how many races run, whether “bumper” (flat races for steeplechase bred horses), hurdle or steeplechase, prize money earnings, handicap rating, and also brief veterinary history. The aim of the study was to compare pelvic rotation in 20 sound horses to the incidence and degree of pelvic rotation in a group of 20 horses with SDFT strain in either one or both forelimbs. Both the sound horses and the injured horses were in training with the same trainer, and therefore had used the same gallops, and underwent the same training regime. Although no significant difference was found in the number of horses with pelvic rotation in sound horses compared with the number of horses with tendon strain, there was a high incidence of pelvic rotation in the group as a whole, with a predominance towards pelvic rotation on the right.

This could have been due to training methods or gallops used, and certainly warrants further research. There was no significant association between side of pelvic rotation and side of forelimb tendon strain, but again warrants further investigation using a larger number of horses. Due to the prevalence of right side pelvic rotation it would not have been possible to show any significant associations anyway between left and right forelimb injury. The study did present some trends for age of horse, sex, and race history; showing that the number of horses with pelvic rotation and tendon injury increased with age. Geldings tended towards a higher incidence of tendon injury, and mares tended towards a higher incidence of pelvic rotation. There were equal numbers of sound and injured horses for each race type, but the degree of pelvic rotation in horses that had fallen was notably larger than in the horses that had not fallen.

FUTURE STUDIES INTO PELVIC ASYMMETRY

The preliminary investigation as described above has formed the basis for further research into abnormal pelvic alignment in racehorses, and whether or not there is any association between side of misalignment and side of forelimb injury. Further research is due to be carried out with a larger sample of horses, and from different yards, to investigate whether there is any prevalence as to the side of misalignment, or if pelvic alignment is affected by training methods and the use of different gallops.