Can protective boots really support joints and tendons?

by, Dr. David Marlin, Scientific and Equine Consultant

Many people apply boots to horses’ legs too tightly. This may be for fear that they will come undone or move, in which case they are likely either of poor design or a poor fit. However, people often say that they put them on tight to give support to the soft tissue structures such as the tendons or the joints, and these claims are even seen in the marketing literature and adverts of some companies. There is minimal information to suggest that boots designed for training and competing provide support for soft tissues or joints. A boot may reduce the range of motion (flexibility) of a joint for example, but this risks moving the load from one structure to another and this may not be beneficial. Tight boots can also result in discomfort and rubbing injury. Just try strapping your ankle tightly over the Achilles tendon area and then go for a run! You will feel pain in the Achilles with each stride and you will modify how you run. Afterwards you may developing swelling and significant pain around the Achilles and also have pain in your knees and hips. It’s not only boots; it’s not uncommon to see bandages applied over-tightly in the belief that this offers “support” for joints and tendons. So appropriately designed boots have the potential to protect the lower leg against both concussive and cutting type injuries caused by hitting objects such as fences or from interference from other limbs. But there are a number of potential downsides to using boots which should be considered and this may help when trying to decide whether to use boots or not or which boots to use.

Quote from Dr Rachel Murray, Orthopaedic Clinician and Researcher at the Animal Health Trust Newmarket: “There is minimal information to suggest that boots provide support for soft tissue or osseous structures. The anatomy of the limb has the digital flexor muscles located proximally. This means it is difficult to provide support for the entire limb taking account of the muscle body. If a boot is used to reduce the flexibility of the limb, then there is a risk of load moving from one structure to another that has not been adapted to experiencing this load magnitude or direction.”

The weight of boots

Firstly, any weight added on to a horse will require an increased effort on the part of the horse to move that weight. This is of course true of a rider and tack. However, kilo for kilo, weight placed on the end of the limbs will have a greater impact than weight carried in the saddle area. The reason for this is that the limbs are moving faster than the main body. The need to be able to accelerate the limbs quickly explains why they are so light when compared with the rest of the body. Animals with big heavy legs cannot move them as fast. This is also why there is not much on the lower legs other than bone, some tendons and a small amount of muscle. All unnecessary weight has been “removed”. Any weight added requires more energy to be put in to get the leg moving and more energy to stop it and make it swing back again. Thus, adding small amounts of weight to the end of the leg in the form of a boot increases the effort the horse must put in to run. It is possible to measure the difference in energy to run between a horse wearing ordinary steel shoes (~260g each shoe) and the same horse wearing aluminium racing plates (around 80g per shoe), a difference of only 180g per shoe. In addition, not only can weight increase energy needed for exercise it can also alter the way the horse actually moves its legs (i.e. its gait). Some of the cross-country boots on the market for example weigh as little as 130g each whilst others are over double this. We should also take into account the potential for boots or bandages to absorb water when in use. Boots that weigh only around 200g each when dry may well be able to hold 100-200ml of water and as 1ml of water weighs 1g, this could double the weight of the boots if the horse was exercising in the rain, on wet grass or going through water. And the weight of the boots is also likely to increase if they do not allow sweat to evaporate and it gets absorbed by the boots.

Restriction of movement

The next issue relates to restriction of movement. If boots are constructed of inflexible (i.e. stiff) material or if boots are applied too tightly, they have the potential to restrict joint movement. This can lead to abnormal loading or patterns of movement with an increased risk of injury. There are relatively few scientific studies in this area but Kicker et al. (2004) published a paper in the Equine Veterinary Journal in which they looked at 3 “support” boots and 1 “protective” boot. At walk, 2 of the support boots restricted the range of movement of the fetlock joint, whilst at trot all 4 boots reduced maximum extension. An undergraduate BSc student study at Hartpury college by Jadine Birchall also seems to support these findings. The average range of movement of the fetlock joint in five horses during walk, trot and canter exercise was 42° (degrees) without a boot and only 36° with a boot. Remember that restriction of movement may cause discomfort and injury.

Trapping of material between the skin and the boot

Materials such as stones, twigs, sand, arena surface, mud, etc can become trapped between boots and the skin leading to abrasion and infection.

Restriction of blood supply

Tight boots and bandages can restrict blood flow in superficial blood vessels leading to pain and tissue damage.

Insulation and heating

The next issue with boot and bandage use during exercise relates to heating. Tendons are elastic structures and as they are repeatedly loaded/stretched (when the limb is on the ground) and unloaded (when the limb is in the air), they generate heat. Some work at the University of Bristol showed that the temperature inside the tendons of horses galloping without boots on could reach 45°C, second only in the body to muscle temperatures. The tendon temperatures are very high not only because of heat production within the tendons but because tendons have a relatively poor blood supply, which in any other tissue would help remove heat. In 1997 the same group published the results of a scientific study in which they showed that tendon cells in a test-tube were sensitive to heating. When the tendon cells were heated for 10 minutes at 45°C, around 10% died, but when they were heated to 48°C for 10 minutes then around 80% died. These results were also confirmed by a more recent study of equine tendon cells in Japan. This study also showed that the higher the temperature, the more tendon cells that died and furthermore, showed that inflammatory mediators were released after heating. Inflammatory mediators are chemicals and hormones within the body that cause inflammation (heat, swelling, pain) and tissue damage. If tendon core (central) temperatures can reach 45°C during a few minutes galloping without boots, it is almost certain that they will get even hotter when boots are being worn. It would therefore seem important to make sure boots are used only during the period of actual exercise and not left on for long periods when the horse is not active, especially after exercise. Removing boots soon after exercise and cooling the legs would also seem to be advisable.

Sweating and skin health

The fact that the lower leg gets hot during exercise and even hotter when boots are used presents another potential problem: sweating. When boots are removed the leg underneath is often very wet from sweat. When skin is in contact with moisture for a long time it becomes hyper-hydrated; this is the effect you see if you stay in the bath for too long. Wet skin cannot “breathe” normally, and it becomes more permeable allowing greater absorption of anything on the skin. Wet skin is also more susceptible to mechanical damage, with an increased risk of abrasions and grazing. Finally, wet skin is also more susceptible to bacterial or fungal attack and hence a potentially increased risk of conditions such as mud fever, caused by the bacterium Dermatophilus congolensis.

Summary

Riders should weigh up the pros and cons of using leg protection on horses. Different types of leg-wear give different protection. For example, bandages will clearly not offer the same protection as a cross-country boot. In addition, the level of protection offered by the same type of boot from different manufacturers can vary dramatically. Unfortunately, at this time there are no universal standards for equine leg protection as there is for example for hats or body protectors. It is also not possible to judge the effectiveness of boots based on appearance, price or advertising claims. At present, the best advice is probably to look for a light boot that is flexible, allows air to circulate and sweat to evaporate, that is not too absorbent and ask the manufacturer what form of testing for concussion and penetration protection that they undertake.

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