Research into how the design of knee blocks on a dressage saddle can impact on the horse’s movement by influencing the rider’s position is due to be presented at the BEVA annual congress next year, while a new system has been developed to track every aspect of the rider’s position in 3D. H&H finds out more...

The importance of rider biomechanics to horse and rider movement and welfare has come into the spotlight with a groundbreaking recent study, and a separate system based on crustacean vision.

Russell MacKechnie-Guire told H&H of his new researches into the effect of knee block design, while in an entirely separate project, Ilse Daly spoke of how investigating mantis shrimp led to her setting up Blackdog Biomechanics, a rider training system.

Dr MacKechnie-Guire explained his research, accepted for presentation at the British Equine Veterinary Association’s annual congress next year, shows that the design of the knee block plays a “crucial role” in allowing the rider’s pelvis to stay in the neutral position, which benefits the horse’s movement.

The researchers used three-dimensional motion-capture devices under the saddle to record spinal movement, pressure mats under the saddle and rider’s seat, and markers on the rider to record movement patterns – and on the horse to analyse gait. They compared elite-level dressage riders in a standard knee block and one with multiple layers, including shock-absorbing material, that allowed the knee more freedom.

They found the restriction caused by the standard block pushed the riders’ pelvis back, the seat bones moving from the lowest part of the saddle to the rise of the cantle.

“With the knee jammed into a big block, the rider is pushed back, hollowing their back as a result,” Dr MacKechnie-Guire said, adding that with the altered blocks, there was a 15% decrease in spinal rotation in the key T13 area of the horse’s back; increased rotation has been shown in studies to be related to spinal instability.

“The restriction destabilises the horse’s back, which makes sense, as the rider’s centre of mass isn’t aligned with the horse’s.”

The researchers also found increased lateral movement, or suppleness, of the back behind the saddle, which they believe allows better transfer of power from the hindlegs.

The riders all reported feeling more “in sync” with their horses in the altered blocks, which fitted with the fact their centres of mass were found each to be more aligned with their horses’.

Dr MacKechnie-Guire said: “Riders and trainers have always known that a rider with a neutral pelvis and evenly balanced seat is easier for the horse to carry, and this study shows there is indeed a significant effect on equine locomotion. Gait analysis showed an increased range of knee, elbow and hock flexion in the modified saddle.”

He added that while riders should not feel they must rush to buy new saddles or knee rolls, they should be aware of the issue when next having a saddle fitting or upgrade.

And he said the study shows once again the importance of biomechanics.

“It’s essential riders at all levels consider all factors,” he said. “I’m for ever talking about how horses will develop locomotor strategies to compensate for any pain or discomfort; they can feel a fly.

“If you’re out of balance, you create an asymmetric rotation around the horse’s central axis, it develops a strategy to compensate and that becomes normal. Then you may lose one bend – and pull the rein to try to manufacture it, but your steering wheel is turning your horse the other way.

“People need to work with their teams; vet, saddler, physio, coach, and consider every aspect.”

Tracking the rider in 3D

Dr Daly explained that her speciality is animal vision and that to study that of the mantis shrimp, whose eyes are on stalks and move in all directions, she conceived a system that would track vision in 3D. At the time, she was keeping her horse at a yard with no arena mirrors and could not afford training, but felt her upper body position needed improvement. She realised she could adapt her shrimp techniques to track her position.

After a great deal of work, she created a system of chessboard markers, worn by the rider, from which software can track every aspect of the rider’s position in 3D. A report is then generated on the spot, on what the issues are and how severe, and the rider can see herself as a 3D stick figure, to visualise her issues.

“It’s not intended to replace coaches, but to give riders more feedback and coaches help to see more,” Dr Daly said, adding that the programme identified an issue she had with one hip. Once corrected, she noticed freer movement in her horse.

“Positional issues can have such a huge impact,” she said. “What you do with your head, shoulders and hips makes massive changes; even a small shift in position can mean you’re not giving your horse the aids it needs.”

Dr Daly added that she is building a network of human and equine physios, so any issues can be referred to them and their feedback incorporated.

“I think we lag behind some sports in not being as joined-up, or using technology as much as we could,” she said. “I think technology can start to play more of a role in the equestrian world and I’m really excited about being part of that.”

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A horse fitness tracker that can also be used to detect problems with gait has been launched in the UK, receiving a highly commended award at the BETA International trade fair.

The Estride can be used with one, two or four nodes that are fitted to boots on the horse’s legs and collect data on training time, stride count, gait pattern, session regularity, horse stability and calorie burn for both horse and rider.

Utilising machine learning algorithms, the equipment is able to “learn” from the horse’s stride patterns to build up a pattern of consistency. When used with all four nodes, the tracker will flag early indications of changes to the stride, making it a useful tool for rehabilitation.

The device has been invented by Chichester-based leisure rider and analytics specialist Arpan Bhatia, who has also created a pressure sensing mat — the Estride harmony — to feed back data on saddle fit.

The two devices can be used together to show the impact of saddle and rider on the horse’s way of going.

The harmony device is the first time a pressure sensor has been available at a price point aimed at home users, and employs 920 sensors to capture data as fast as every 200miliseconds while a horse is being worked.

“There are similar devices out there but they are not quite the same — at this point no one else is really using stride-related algorithms. The other mats that are available are 10 times more expensive and haven’t evolved over the past 10 years, even though the technology has moved on,” said Arpan, who been working on the products for the past year-and-a-half, along with a team of 15 others.

“I made it because I bought a new horse and the saddle it came with wasn’t right. A saddler came in and helped me, but couldn’t give me evidence of why the existing saddle was a problem and I needed to spend £2,000 on another one.

“Using the mat and tracker together, you can check the stride patterns between two different saddles and have biomechanical evidence of a problem. If the horse is skipping or missing a beat, and the saddle is OK, then you might have an inherent problem with the horse,” he explained.

Both devices sync data to a cloud via an app, with the information accessible from anywhere in the world. Users can also input data on the types of surfaces they are riding on to build an accurate picture.

“Everyone likes to use a smart watch fitness tracker and horses are as expensive and important as anything else,” said Arpan, who describes himself as “a lover of data”, with a background working in analytics for media, government and military.

“Even if you just use the tracker for hacking every day, it can record useful information on stride and calorie burn — I have a mare who is a bit fat at the moment and I know what I need to do to control her diet. I’ve use data from various research papers based on breed, age, sex and weight to assess calorie burn and we might also create a calorie consumption model going forwards,” he added.

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As well as horse owners, Arpan sees the products as being a potentially a useful tool for saddlers and vets.

“We had good feedback at BETA and the Society of Master Saddlers were interested. We also have a couple of vets trialling it at the moment,” he said. “I could see the mat being used by individual yard owners with one mat for every yard — every season horses change shape and it would be useful to check saddle fit.”

The tracker comes with an option on the number of nodes and costs between £299 (with one node) and £599 (with four nodes), while the harmony pressure mat has an introductory price of £349. Both devices are available on pre-order, with a six to eight week wait on the tracker and a 12 week wait on the mat.

For all the latest news analysis, competition reports, interviews, features and much more, don’t miss Horse & Hound magazine, on sale every Thursday.

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Q: My friend recently bought a new horse, and had gait screening done to assess soundness. Can you tell me what this involves, and whether it could benefit my horse?

KC

The screening you refer to is known as equine performance analysis and is used to assess and maintain equine soundness.

Consultant farrier Haydn Price DipWCF developed the video-based system in 2004 to quantify data such as stride length, body symmetry and soundness for the British Olympic horses in Athens.

“Horses are filmed from all angles in walk and trot, on a hard, flat surface with joint centres highlighted,” explains Russell Guire of Centaur Biomechanics, who is the British Equestrian Federation (BEF) Equinalysis technician, and works with the World Class Start and Performance riders and their horses.

“We then collate what’s called ‘kinematic data’, which is downloaded on to a CD or DVD,” he explains.

“The screening can be used to help identify the cause of training problems, such as a difficulty in performing lateral work on a certain rein due to asymmetry or conformation issues.

“Although the technology began at the top levels of competition, these ‘video evidence’ techniques are also now accessible to ‘normal’ horse owners.”

The technology is being used at Bushy Equine Vets in Gloucestershire by Ian Camm MRCVS.

“Health and performance screening can potentially extend a horse’s competitive life by establishing a profile of movement and soundness,” explains Ian.

“The resulting ‘baseline’ of facts, such as the alignment of the joints, can be useful during the training process, and I believe has great potential in the field of assessment.

“The technology can be used to clarify any lameness or biomechanical challenges picked up at a horse’s five-stage vetting, and evaluate aspects such as stride length, breakover distance and carpal, tarsal or fetlock flexion.”

It can also be used for rider assessment; horse and rider are filmed from all angles and an on-site projector plays the footage back in slow motion. The software identifies the rider’s body measurements, such as posture, body alignment, and hip and knee angles.

Useful for physiotherapy and veterinary work, this system also provides a way for using farriery to promote athletic performance, according to Haydn Price.

“Farriers can take into account the needs of the limb, if required, instead of just shoeing the foot,” he says.

“As well as fitting a shoe to accommodate the horse’s movement, shoeing should take into account the amount of dynamic loading on a limb, which is directly related to the effectiveness of the joints, and can affect tendon and ligament health.”

Regular screening usually takes place annually or biannually at a cost of up to £250 per session. The technology can be utilised by all para-professionals and professionals, including equine vets.

Information

Visit www.equinalysis.co.uk for details about accredited clinicians who carry out the service, or Tel: 01291 671351.

This Q&A was first published in Horse & Hound (31 May, ’07)

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What is upward fixation of the patella?

As the horse has evolved it has undergone a multitude of physical changes designed to help it survive. One such adaptation is the development of a “locking” mechanism in its stifle that keeps the hindleg in extension and allows the horse to rest while standing, with virtually no muscular effort.

This normal anatomical feature becomes abnormal only when the stifle inadvertently locks at the wrong time, or when the unlocking mechanism fails. When this happens it is known as a locking stifle or, more correctly, upward fixation of the patella (UFP).

UFP is the most common cause of stifle gait abnormalities, although it is not usually responsible for lameness. It tends to be seen mostly in young, immature horses and ponies, with Shetlands especially prone.

Why does it happen?

There are various factors that increase the chances of a locking stifle and from these it can be understood why it is recognised more in young, unfit horses or those that have suddenly had to come out of training and are perhaps on box rest, leading to a rapid loss of muscle condition and tone.

• Straight hindlimb conformation: typical of many ponies; the patella is already riding high in the trochlea, so the slightest bad step can allow inadvertent fixation
• Poor muscle tone: typical of young, immature horses; a loose, flabby quadriceps allows the patella to bounce around in the trochlea
• Poor condition: leading to weak muscles
• Poor co-ordination between stifle flexor and extensor muscles: associated with young animals in poor condition
• Hereditary factors: the inheritable nature of straight hindlimb conformation
• Trauma to the stifle: leading to loss of muscle tone and condition

Treatment options

Establishing a conditioning program aimed at increasing the level of fitness and strength of muscle tone, to include:

• trotting on soft ground in straight lines
• walking/trotting up and down hills,
• increasing the scope/variety of feeds
• worming

Injecting counter-irritants (“blistering”), such as an iodine- or steroid-based product, into and around the middle and medial patellar ligaments to make them thicken and shorten. This makes it less possible for the patella to become hooked up. The results are unpredictable, though, and there are possibly disastrous complications should synovial sheath structures be unwittingly involved.

Corrective shoeing with raised heels may help by limiting the degree of extension of the stifle joint, which sometimes causes locking.

Surgical treatments include:

• Medial patellar ligament desmotomy: cutting the medial patellar ligament through a small incision. This disrupts the patellar locking mechanism and was the surgery of choice until recently, due to the one in five risk of post-operative complications.
• Medial patellar ligament splitting: a relatively new technique that involves inflicting multiple incisions into the ligament, resulting in localised thickening and increased stability. Horses are encouraged to resume controlled exercise within days. Initial reports indicate a 95% success rate with no complications so far, although a possible muscle abnormality has been touted to explain the occasional poor response to surgery.

This veterinary feature was first published in Horse & Hound (15 March, ’07)

There is often a fine line between horses who simply have an inherent, slightly “odd” gait (in front or behind) and those who are lame — albeit subtly.

Interest in gait patterns has increased markedly as their relevance to long-term soundness and performance becomes clearer. It is a challenge to decide what is normal when buying a horse. Techniques for evaluating limb movement are becoming ever more sophisticated. The latest computerised technology can now illustrate the subtle variations in movement between individual animals — and even between individual limbs of the same animal — which may not always be obvious to the average observer.

These studies have shown time and again that there is a “grey area” encompassing those situations where an individual gait pattern may, or may not, indicate a problem. Interpretation of hindleg movement can be especially difficult because a problem is often “bilateral” (it affects both hindlimbs equally), thus balancing out and eliminating overt lameness.

In addition, there are several well-recognised variations on hindlimb flight that appear “normal” in certain breeds, or in horses with particular types of conformation. However, in others they indicate a source of pain and should be considered a true lameness.

“Plaiting” — in which the horse swings each hindleg round the other before placing it on the ground ahead of, or to the outside of, the opposite foot — is one example. In horses with severe “base narrow” conformation (the lower hindlegs are closer together) this appears to be their standard way of moving. In other animals it has been traced to hock, sacro-iliac or even suspensory ligament problems.

Another example is where the hindlimb is swung forward outside the expected line of limb flight, eventually landing relatively near the expected spot. This “travelling wide behind” can be an indication of upper hindlimb pain in some horses — but in trotters it represents their normal pattern.

While there are many situations where an odd or unusual hindlimb gait should be considered a true lameness, there are also a number of conditions where a limb flight abnormality results from a musculoskeletal structural problem. These cases are often referred to as “mechanical lamenesses” because the affected limb simply cannot physically bend properly. The horses are not usually in any pain, and many continue to perform right up to expectation throughout their lives. Others physically cannot, especially if the gait abnormality becomes profound, even though they are in no discomfort.

There are other examples of odd or unusual hindlimb gait patterns, plus additional possible “mechanical lamenesses”. Many are secondary to a problem elsewhere in the body, such as in the back, or to a general illness that has various knock-on consequences, such as tetanus.

While it is tempting to dismiss a slightly bizarre gait pattern as “just the way he’s always gone”, there could be a source of pain somewhere — or it could represent a very subtle form of a mechanical lameness. Either way, veterinary advice should be sought to give treatment the greatest chance of success.

• This veterinary feature was first published in Horse & Hound.For more information about abnormal gaits visit the veterinary advice section of the new HHO horse care archive

Stringhalt

Stringhalt is a poorly understood neuromuscular disorder in which the nerves to the muscles are afflicted. It results in a mild to severe “hyperflexion” (extreme flexing upwards) of one or both hocks. This is shown as a sudden jerking up of the limb, either occasionally or with every step, sometimes such that the hoof strikes the horse’s belly. It is most obvious at walk, on turning or on backing up.

Despite its “violent” image, most horses remain remarkably unconcerned. The cause of the nerve degeneration is unknown but may be a result of trauma. An Australian version of stringhalt has been linked to the ingestion of plant toxins from poor quality pasture.

If the condition is mild, horses can cope. But the surgical cutting of the “lateral digital extensor muscle”, reducing the “snatching up” action, may be considered in severe cases.

Shivering

Like stringhalt, but less common, this is an ill-defined neuromuscular disease. It may be dietary in origin, or may be a complication of a viral or bacterial infection.

It is characterised by an involuntary elevation of a hindleg — and often the tail as well — which then quivers and shakes, before returning back down. Occasionally there may be fine body tremors too. The signs, which can vary from day to day, are worse when backing or going downhill.

Shivering tends to become progressively worse, and there is no treatment, although some control of early cases can be achieved with a high fat and low carbohydrate diet.

Fibrotic myopathy

In this condition there is a sudden “slapping down and back” of the hindlimb during its forward movement, shortening the movement. It is most obvious at walk and is often confused with stringhalt, although careful observation shows there is no hyperflexion.

It is usually caused by a traumatic injury to any of several hindlimb muscles, classically during sudden “stop and turn” type exercises, experienced by polo ponies or Quarter Horses. This muscle tearing results in areas of fibrosis, and even ossification, within the damaged muscle, which also eventually begins to reduce in size. Ultimately muscle function will become compromised. In some cases, the hard, knotted areas can be felt on the backs of the hindquarters.

Physiotherapy to stretch the damaged muscles helps many horses with fibrotic myopathy. But in severe cases surgery may be required to loosen, or even remove, the knotted muscle mass — or to transect it at its bony attachment.

Upward fixation of the patella

This occurs when the patella (or kneecap) becomes locked over the outside of the “trochlear ridge” of the thighbone within the stifle, causing the characteristic rigid extension of the stifle and hock. The leg remains like this until the hindlimb muscles are able to lift the patella off the trochlear ridge, so allowing the stifle to flex once more.

It is usually seen in younger animals in poor condition, especially those with straight hindlimb conformation, or those who are off work and are unmuscled.

The condition can affect one or both hindlimbs, can be intermittent or permanent, and can vary from mild (where an occasional “clicking” is heard, or a slightly “jerky” action noticed) to severe, where the stifle becomes stuck in extension for distressingly long periods.

Treatment is aimed at improving and maintaining the animal’s condition and level of fitness. The injection of irritants into the patella ligaments, or shoeing with raised heels, has also been tried. Surgery to cut the inside patella ligament is only now used as a last resort because of its known association with subsequent patella fractures or degeneration.

• This veterinary article was first published in Horse & HoundTo read more about gait abnormalities and lameness visit the HHO horsecare archive at www.horseandhound.co.uk/horsecare/

New thinking suggests that both shivers and stringhalt (as explained here) may have similarities to certain muscle disorders that can be managed effectively with a change in diet.

Findings from a researcher in America suggest that both these conditions may be related to ERS, the muscle syndrome that we most commonly refer to as “tying up”.

While the name of Dr Stephanie Valberg is synonymous with defining certain cases of ERS into two new syndromes, polysaccharide storage myopathy (PSSM) and recurrent exertional rhabydomyolosis (RER), a second researcher, Dr. Beth Valentine, a vet from Oregon State University, has now made the link between a related condition, equine polysaccharide storage myopathy (EPSM), and muscle conditions of heavy breeds.

In her opinion, shivers and stringhalt are manifestations of EPSM in these horses.

In susceptible horses, both conditions seem to centre on the rapid accumulation of glycogen in muscle cells after starchy, sugary meals, which in turn causes damage to the cells. Management practices have been proposed to reduce the likelihood of occurrences, involving a chance in diet and exercise patterns.

Dietary changes involve reducing the amount of starch and sugar in the diet, replacing them with fibre and oil, with training adaptations to make muscles burn fibre and oil as energy sources.

These changes are not a panacea, however, and will not eradicate shivers or stringhalt in every case, pointing to the gaps in our knowledge about the interactions between the nervous system and muscle function.

Feeding the shiverer

• Prevent excess accumulation of carbohydrate in the muscles, by diet, exercise and short lay-off periods.
• Diets should be high in fibre and oil and low in starch and sugar.
• Starch and sugar foods include mixes (typically a minimum 25% starch and sugar, but often well in excess of 30%) and cereals (oats 50%, barley 60% and maize 70% starch, and minimal sugar), and grass (2-3% sugar in every bite).
• Draught horses and part-breds tend to be good doers and therefore require less food to sustain them. This makes it easier to avoid high-energy, high-starch mixes.
• A typical diet of 8kg hay, 3kg chop and 1kg oil supplies 3,500g fibre, 190g starch and 900g oil per day. Some horses dislike this much chop and oil, and so a handful of chop, 4kg of a low starch compound and a generous glug of oil will supply 3,200g fibre, 500g starch and 650g oil. These levels are compared with feeding mix at similar levels.
• This feed feature first appeared in H&H (31 October 2002)

Hunters require powerful hindquarters to do their job properly, yet some of these horses – particularly big, heavy hunters – can move their back legs in a very strange way at times.

These off hind limb actions are most noticeable as they move off, often quite briskly, after standing around getting cool. The observer can be left wondering whether they are lame or if they have a gait abnormality.

If they are still going strong at the end of the day’s hunting, such an abnormality may not actually be that important to the horse.

However, they may feel rather odd the first time you ride them, and this could be a work at a veterinary examination for purchase.

It is worth knowing which hind limb movement disorders are significant or serious. The following three are a common cause for concern:

Stringhalt

This is a hind limb gait abnormality with an exaggerated bending of one or both hindlegs, almost like a goose-stepping march. It is most obvious at a walk, particularly after a horse has been standing still in cold weather, such as after the meet), yet the horse will be normal at rest.

Signs are worse on turning and backing, and only one hindleg is usually affected.

• In the UK, the exact cause of stringhalt is unknown, but it is due to a motor nerve abnormality rather than a disorder of the musculoskeletal system. Some cases follow trauma to the hock or a tendon of the lower limb (the lateral digital extensor tendon).
• There is no magic treatment for the conventional stringhalt seen in the UK. Some cases are treated by surgery on the lateral digital extensor tendon, but, at best, the success rate is no more than 50%.
• If you have a suspected case, it is important to get your vet to confirm that it is stringhalt, as it can be confused with other conditions, particularly upward fixation of the patella.Locking stifle
  This is more properly called upward fixation of the patella. It is a mechanical lameness where a horse or pony is unable to unlock the stifle (or kneecap) from the extended position, so the horse hops forward with its leg stuck out behind. The toe may be dragged along the ground and the stifle and hock cannot be bent.It can look quite alarming and, at first glance, many people think that the limb is broken. Fortunately, the kneecap (or patella) does not lock, but catches with each stride.It may be more obvious when the horse is reversed or turned towards the affected side. When the stifle is not locked, the horse or pony will not be lame.
• Upward fixation of the patella occurs more commonly than stringhalt in ponies, but the two are easily confused. It is worse in horses in poor general condition or lacking fitness, and improves with increased work and better muscle tone.
• Upward fixation of the patella can often be easily treated. Many animals simply grow out of it, others respond well to a change in exercise pattern, while a few require surgical treatment.Shivering or shivers
  This is another mysterious and poorly understood disease of the nervous system. Farriers are probably most aware of the condition and know how common it actually is.This is because one of the biggest problems with horses which shiver is that they can be difficult to shoe. Such horses have a tendency to snatch the limb up, or for the limb to quiver when it is lifted. This in turn makes accurate fitting of shoes arduous.
• Apart from problems during shoeing, a horse who is a shiverer may to all intents and purposes appear normal. In many cases, it may not actually affect its performance.
• The signs associated with shivering may vary enormously from case to case and from day to day. The signs are inconsistent and can be easily undetectable on a one-off examination, which can make it very difficult to spot when assessing a horse before purchase
• The disease tends to start gradually, so that it may be obvious on one occasion and not there the next..
• Shivering is said to be progressive and may gradually become worse. But there is no way of predicting if or when they will get worse. Some horses spontaneously recover, while sometimes a rest can cure the problem.
• Traditionally, it is thought that shiverers are able to cope with flatwork, but their jumping ability is impaired. Some do cope without major difficulty, however.
• There is an unproven suspicion that the condition may be inherited. It seems to appear in certain breeding lines and a familial tendency is suspected. Mostly, it is seen on large, heavy adult horses, primarily draught horses, heavy hunters and warmbloods.Is it in the walk?
  Many horses with gait abnormalities remain undiagnosed, so is it just the way they walk?
• This article first appeared in H&H (31 October 2002)

Shivering, or shivers as it is also known, is a mysterious and poorly understood disease of the nervous system.

Farriers are probably most aware of the condition and know how common it is because horses that shiver can be difficult to shoe. Such horses have a tendency to snatch the limb up, or for the limb to quiver when it is lifted, which can make accurate fitting of shoes difficult.

Apart from problems during shoeing, a horse which is a shiverer may appear normal. In many cases, it may not actually affect their performance. The signs associated with shivering may vary enormously from case to case and from day to day.

The signs are inconsistent and can be easily undetectable on a one-off examination, which can make it very difficult to spot when accessing a horse before purchase.

The disease tends to start gradually, so that it may be obvious on one occasion and not there the next. This can lead to major problems at purchase as the horse may suddenly be seen to be a shiverer immediately after it has been sold.

Shivering is said to be progressive and may gradually become worse, however, I have seen many horses with mild shivering who have not shown any obviously deterioration over several years. There is no way of predicting if or when they will get worse.

Traditionally it is said that shiverers will be able to cope with flatwork, but their ability to jump will eventually be impaired. Yet certain competition horses have mild signs and cope with work without major difficulty. Some get better with rest and others recover spontaneously.

Problems arise short-term with shoeing and sometimes more long-term if the horse is sold. Technically, shivering is considered an “unsoundness” because of the uncertainty associated with it.

Breed societies are particularly concerned about shivering, as there is an unproven suspicion that the condition may be inherited. It seems to appear in certain breeding lines, with large, heavy adult horses, including draught horses, heavy hunters and warmbloods most commonly affected.

Signs of shivering

• Muscle twitching, particularly involving the hindlegs, pelvic area and tail. This may be seen as trembling or shivering in the limbs and holding the tail up.
• The shivering frequently worsens when the horse is backed or turned in tight circles
• Difficulty lifting up the legs, which is noticed when the horse is shod
• The horse may stand on its toes with its heels raised off the ground
• The forelegs are rarely involved, but occasionally an affected horse may stick out a front leg, or hold it bent at the knee and that leg will shiver
• Rarely, the head and neck may be involved, with the ear or lip twitching, the eye blinking rapidly or shivering of the neck muscles
• In severe cases, there may be muscle wastage related to the shivering episodes
• In between bouts of shivering the horse may seem absolutely normal
• Stress and excitement can occasionally trigger signs
• Some affect horses show signs when bought out of the stable in the morning, with signs becoming less obvious or even absent after exercise
• One or both hindlegs may be held off the ground and stuck stiffly out to the side as the muscles quiver, which can result in the horse falling over

This article, which also covered stringhalt and locking stifle problems, was originally published in the 31 October 2002 issue of Horse & Hound. To purchase a copy of this issue of the magazine (tel: 020 8532 3628).

Q. I have a three-year-old ID X TB mare who, after an injury to her hind leg last August (and subsequent loss of condition), started to display fixation of the patella. She has now recovered from the injury and has put weight and condition back on, but still experiences what I can only describe as a ‘collapsing’ of her rear end.

While it is not obvious all the time, and doesn’t appear to cause her pain, it is very worrying. Should I ask a horse physio to have a look at her? My vet says that if the fixating doesn’t disappear, a minor operation can be performed – what are the implications of this?

Vet Jo Holmes answers: “It appears that your mare has developed upward fixation of the patella (kneecap) due to muscle wastage of her quadriceps muscles while recovering from her injury last year.

“The ‘quads’ unlock the stifle joint when the horse moves forward – otherwise, the stifle can lock as part of the ‘stay apparatus’ of the hind limb, preventing stifle flexion.

“When the quads contract, they should pull the middle and medial patellar ligaments off the end of the femur to free-off the patella itself, allowing full-range joint movement. If this does not happen, the stifle remains locked in extension and the leg is dragged behind the horse. Over time, this will damage joint ligaments and cartilage irreparably.

“In some cases, there is only intermittent catching of the joint, especially in young horses who are not yet musculo-skeletally mature. It is advisable to delay surgery to cut the medial patellar ligament in these cases, since they are likely to mature out of the problem. In time, your horse may also develop enough muscle to overcome the condition.

“Surgery is fairy straightforward and can be carried out on the sedated horse using local anaesthetic. There are some reports of premature stifle arthritis in horses who underwent this operation in their youth, but the risk has to be weighed against the risks of chronic stifle joint inflammation if the operation is not carried out.

“A physio may be able to help you build up the quads, but correct exercise should work as well. I would suggest building your horse up carefully using uphill work in walk and trot.”

Q: I own a 16-year-old Welsh Cob. When he was four years old, he had an upwardly fixated patella (stifle) and had to have the ligament cut to release it. Twelve years on, the stifle is starting to slip out again. Is there anything I can do to stop this happening?

Jo Holmes MRCVS replies: The operation that your horse had 12 years ago is less commonly performed nowadays, and instead of cutting the ligament, we treat this condition by trying to build up the horse’s quadricep muscles to assist in unlocking during exercise.

The first thing I’d recommend is that you put your horse on a supplement which contains shark’s cartilage and is specially designed to encourage joint flexibility, such as Cortaflex by Equine America.

Start a careful exercise programme. Begin by walking your horse up hills and then later, as he becomes stronger, do the same in trot. This will help to build up his quadriceps and improve his muscle tone, and should also help to maintain joint alignment, giving the stifle some support. Long term, I’m afraid the joint may become arthritic due to his operation.