Leg protection for event horses ? latest findings | Eventing Worldwide

Dr David Marlin Lecture for USEA, sponsored by Trizone and World Equestrian Brands.

For those who don?t have time to watch the whole thing (although I recommend it very highly, it is fascinating stuff) here are some of the most important points David Marlin (pictured right) made:

There is a predisposition for the lowest part of the horse?s forelegs to be injured, especially the Digital Flexor Tendons.

This can be from an acute injury, or from repeated trauma over many months that leads eventually to a severe rupture – for example from concussion. Think of hitting a metal pole against something hard, and the juddering afterwards that goes through your arm and your body; that is concussion.

A horse which hits fences regularly will incur this, and it can cause severe internal injury. Repeated bouts of low-grade trauma, from hitting fences, or from repeated slight interference injuries can lead to an inflammatory response within the tendon, within the joint, within the bone, and over time this builds up to be a serious problem, and can predispose the horse to eventual failure. There may be no outward signs.

Particular concerns

? Horse with bad conformation, horses that are tired, horses with a previous injury, or with an existing injury that perhaps hasn?t been dealt with.
? Heavy going, hard going, uneven going.

The problems

Injuries can come from hitting fences, falling, or interference-type injuries from brushing, speedy-cutting, overreaching.

Horses? cannon bones can be compared to our shins ? there is no muscle to protect the bone at the front. The tendons at the back of the leg are similarly vulnerable. They are subject to rapid acceleration (the horse?s leg can be moving at 3 to 4 times the speed of the horse?s body itself, it has to be brought to the front and out to the back very quickly), very high loads, and have very little protection, with no muscle mass to protect the area.

So, protection is needed, but there are potential concerns with boots:

Weight

The further down the horse?s leg we place a weight, the greater the effect will be. The horse has to make more effort to move the leg once any weight is attached. Shoes ? a 3oz aluminium racing plate compared to a 9oz steel shoe ? 8% to 9% increase in energy needed JUST to run with the heavier shoes on. Some boots when wet (having gone through the water jump, or absorbed sweat from the horse?s leg) will double in weight, from 10oz to 20oz.

Implications of weight in boots
. Increases effort
. Alters gait ? interference (this may be an issue in prolonged exercise)
. Earlier fatigue, poorer performance. This could lead to the horse not jumping so high (hitting xc fences, or having poles down)
. Of the boots tested, the dry weight varied from about 4 oz to 9 oz

Stiffness of the boot materials
. Boots need to be flexible, especially around the fetlock area, and comfortable for the horse

Support
Boots do NOT provide support to the joints or the tendons.

At the moment our understanding is that you cannot support the joints or the tendons with boots, however tightly you put them on ? in fact you are probably predisposing your horse to injury if you over-tighten a xc boot. So called ?support boots? reduce the range of movement of the fetlock joint. The horse has got his conformation for a reason, and when we start messing around with it, we are very lucky if we make it better. Affecting the range of movement of such an important joint is not advisable unless you know exactly what you are doing.

Fitting the boots

Tight application of boots is an important issue – people seem to fit boots tightly because they don?t want them to slip. But, if you have to fit a boot tightly, or tape it on, then it simply doesn?t fit that horse, or isn?t well-designed. A good boot should not need to be put on tightly, and should stay in place when you are riding.

Boots fitted tightly can affect the range of movement of the joints, as well as causing abrasion over the tendon, leading to tendonitis. Arena material, mud or dirt trapped under a boot can cause nasty abrasions or infections.

Heating

Tendons heat up because they are elastic – and if you play with an elastic band, continually stretching and releasing it, it will heat up. Tendons get very hot when galloping.

Study done at University of Bristol: horses were galloped without boots, on a treadmill, with tiny temperature sensors in the tendons and muscles. The muscles got to about 47 degrees C, and the tendons to temperatures of about 45 degrees C. However, the muscles have a good blood supply, and blood acts as a coolant which can literally carry the heat away, whereas tendons are well known to have a poor blood supply, so are far less efficiently cooled.

Another study done at Bristol: 10 minutes at 48 degrees C is enough to kill about 70% of the tendon cells in a sample.
A recent study in Japan: 5 minutes at 42 degrees C is enough to kill almost half the tendon cells.

This was ?in vitro? (in a petri dish) and sometimes cells behave differently in a petri dish to the way they behave in the body, BUT there is no doubt that these cells are heat-sensitive.  Heat has the potential to produce inflammatory responses and death in tendon cells. The heat damage will set up an inflammatory reaction, and inflammatory mediators which are introduced by the dying cells will cause direct damage to the tendon. Boots can prevent heat loss, can insulate the legs (which are, obviously, designed to be naturally air-cooled!) which can be disastrous.

Protection ? against a penetrative blow, against a concussive blow

Doctor Marlin showed videos of different forces, both concussive and penetrative (of 1.25 to 20 Joules) being tested independently on different boots. (In his example, an apple dropped onto your foot from 1m height is about 1 joule, a brick dropped onto your foot from 1m height is about 20 joules. 1 joule will cause bruising, 20 joules will break the femur of most humans). Some of the boots tested actually amplified the force of a blow (because the materials from which they are made did not absorb and dissipate the force). They amplified the concussive forces into the tissue; from a 10 joule blow it was amplified up to 20 joules, the level that could break a human femur.

The FEI is considering bringing in certification for horse boots, like the certification required for crash hats and body protectors. Until it does, ask the manufacturer of your horse boots what testing they do.

Boot testing: the important factors that need to be addressed
Weight
Stiffness
Heat Dissipation
Protection

So, in conclusion:

Use lightweight, flexible, non-absorbent boots with proven, tested, good protection against concussion as well as penetration, and which heat the tendons as little as possible. Make sure they fit really well, and do not fit them tightly. Remove them as soon as you can after exercise, and get some cold water, cooling boots, or ice boots on those vulnerable tendons as soon as you can. If your horse is the high-on-adrenalin, bit-of-a-nutcase-after-cross country type, either take studs out first, or swap cross country boots for cooling boots immediately, then take studs out as soon as you can. Bare legs + studs can be a disastrous combination.

Words Kerry Weisselberg

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