No Foot, No Horse

The first in a series of 3 articles aiming to assist you in understanding the mystery of the horse's hoof

To many, the horses hoof is an incredibly mystical structure, often misunderstood and mistreated due to lack of understanding. This is the first of three articles coming over the winter months, designed to help manage your horse's feet to keep them happy and healthy over the next few months.

THE ANATOMY
The horses hoof is the equivalent to the human middle finger, consisting of three bones. These have different names which can be confusing so we will clarify them:
1. First phalange, proximal phalange or long pastern
2. Second phalange, middle phalange or short pastern
3. Third phalange, distal phalange or pedal bone

These bones create the fetlock, pastern and coffin joints. The fetlock is the joint between the cannon bone and the long pastern bone. The joint between short pastern and the long pastern is the pastern joint. Between the short pastern and the pedal bone is the coffin joint.  The hoof surrounds the pedal bone, the navicular bone and part of the pedal bone.

The hoof is a very special structure designed to:
1 Resist wear
2 Support the horse's body weight
3 Absorb concussion

The hoof itself is made of modified skin cells which are similar to claws and horns.
The outer part of the hoof has no blood vessels and is not sensitive. It is made up of the wall, the sole and the frog.
The internal parts of the foot are called the corium. Nerve and blood supply feeds the horses hoof to maintain health and growth through the corium.
The digital or planter cushion is a wedge shaped fibro-elastic gel pad which is situated internally at the back of the foot. It fills the heel, lying above the frog and below the deep flexor tendon. The bulbs of this cushion are soft and fatty while the rest is more fibrous. It is not well supplied with nerves so if it is pricked (such as a nail, stone or sharp stick penetrates it) it may not give much pain but serious infection may develop which is difficult to treat. The hoof's role is to absorb and disperse the shock caused by the horses foot hitting the ground.

The lateral cartilages are tough plates of gristle which lay either side of the digital cushion. They attach from the pedal bone and follow the curve of the wall reaching just above the coronary band. In a young horse, the lateral cartilages are soft, flexible and are able to absorb a large amount of concussion. However, as the horse ages, the hoof becomes tougher and less able to withstand the range of movement which may occur during exercise. If injury occurs to the lateral cartilages the horses body can 'repair' the damage using calcium deposits. Calcium deposits which occur on the lateral cartilages severely reduce the amount of concussion they can absorb. This is called Sidebone and needs to be diagnosed by a veterinarian using x-rays.

The pedal and navicular bones have a large blood supply and fit snugly together. The deep flexor tendon (pictured in blue above) fans out to run over the navicular bone and attaches under the petal bone. The navicular bone acts as a pulley as the tendon pulls on the pedal bone during movement. This explains why the navicular bone is prone to injury and deterioration particularly with high level competing.

THE FUNCTIONS OF THE FOOT

There are three main functions of the foot.

Reducing Concussion

The hoof has spent 65 million years adapting to absorb concussion effectively. The hoof wall bears the majority of the impact. For the unshod horse, the hoof strikes the ground, the frog hits first, then the heals, bars and finally the toe. The hoof expands slightly out through the sides. The toe doesn't expand at all due to the tough nature of the hoof wall at the toe.

The impact of the foot hitting the ground is dispersed through the internal structures of the foot. The pedal bone is protected by the digital cushion. It disperses the impact through the lateral cartilage and up through the pedal bone. The shock continues through the ascending bones up the leg.
The greater degree of slope in the horse's shoulder manages the impact better or than a more upright shoulder. This leads to an increased amount of wear on the other leg structures dealing with the concussion, such as the lateral cartilages pedal bone and the hoof itself.

Anti-Slip

When the ground conditions are soft, the toe digs into the turf preventing slipping. The hoof is less effective on hard or greasy ground. The round shape of the horse's hoof creates a suction effect which prevents slipping. This also deserves consideration when the horse is in muddy conditions. The suction of the hoof causes the horse to need more energy to pull its foot out of the mud. This increases strain and injury potential for other areas of the body such as tendons or muscles in other areas of the body.  When the frog is in contact with the ground it prevents slipping. However the modification of the shoe using studs or calkins prevents the shod horse slipping.

Circulation

In the human, moving blood up from the lower leg happens because of the massaging effect of the calf muscles in our lower legs. Horses do not have muscles in their lower legs, so they rely on the hoof acting like a pump, pushing the blood up with pressure placed on it with each stride. As the weight comes off the foot it fills with more blood which is pumped up on the next stride. The blood is prevented from flowing back to the foot by valves in the veins.
The hoof is an amazing structure. By understanding how it is made and what it does we can make choices which assist in keeping your horse's sound and happy during the winter months and beyond!

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