Although not often thought of, every time a horse takes a step a shock wave runs up his leg and through his body. By definition, shock is the effect on an object caused by the energy delivered to it by a force (typically an impact force) over a short period of time. The effect of shock occurs when the energy of the impact is transferred from one object to another, which may cause injury to those objects.
When a horse takes a step at any gait, the frog takes the first hit as the heel strikes the ground and the load is transferred to the toe. The shock wave travels through the frog and into the digital cushion, a mass of fibers lying directly above the frog. The cushion compresses as it helps to support the weight of the horse and absorbs most of the shock. Any shock left over is transferred to the lateral cartilages which cradle the coffin bone, and the rest is transferred onto the coffin bone and through other tendons and ligaments. These tendons and ligaments prevent the shock waves from jarring the spinal cord.
Since the front legs carry most of the weight of the horse, they receive the most shock as they hit the ground. In the hind legs however, there is a hip joint connecting the legs so any shock transferred through the hind legs will also travel through the spine. The cartilaginous disks between the vertebrae help to mitigate the concussion. There are several important confirmation factors that will help decrease concussion to the spinal cord:
- Angled joints are better shock absorbers than straight joints because the tendons and ligaments stretch around the angled joint and absorb more of the impact. In a straight joint, concussion forces are transferred directly from bone to bone through a layer of joint cartilage without mitigation by the elastic ligaments and tendons. Over time the bones and cartilage will deteriorate, resulting in arthritis.
- Hoof size proportional to body size: Heavier horses with small hooves are more prone to injuries because there is simply not enough surface area to help disperse the force.
Even if a horse has good confirmation, excessive concussion can overwhelm the shock absorbers and cause injuries and arthritis. Working consistently on hard ground is a perfect example of excessive concussion. Hard ground wears away the frog, which is the first line of defense in absorbing shock. This means more shock is transferred into the leg, and the tendons, ligaments, and bones can then bang against each other, causing a myriad of issues. Navicular Bursitis can actually be caused by excessive concussion between the flexor tendons and the navicular bone.
To help prevent excessive concussion, many riders choose to shoe their horses. Simple metal shoes are probably the most common choice, and help to lift the frog off the ground. Bar shoes are needed for horses that have Navicular to help raise the heel and increase break over. These shoes are known to relieve stress and decrease the force on the navicular bone, as they don’t allow the heels to sink down so far, which is particularly important in soft footing.
The problem with metal shoes is that they don’t reduce the overall shock to the leg. This isn’t a huge problem if the horse is being worked on soft surfaces, but if the horse is worked on pavement for instance (ex. Police horses), there are other shoes that can help to mitigate the constant shock waves. Polyurethane (poly) shoes are not all that new, but some farriers still hesitate to adopt a different type of shoe. A lot of racehorses have poly shoes because of the synthetic tracks. More and more Jumper and Dressage horse owners have started using poly shoes to help their horses adapt to the synthetic arenas. In theory, synthetic footing is great because it requires little to no maintenance. For the horses, however, synthetic footing is like concrete. There is no give in the footing and many horses require poly shoes to keep them healthy and sound.
Knowing that excessive shock can cause injuries, be careful while riding and make shoeing adjustments if necessary.