Equine Podiatry and Chiropractic

Amy Hayek, DVM

Overall Theme

Any limb that does not complete the phase of stride to achieve normal heel first landing is in danger of damaging the joints of the limb. Limbs that cannot achieve normal heel first landing for whatever reason, place undue stresses on the cartilage, muscle structures, tendon and ligament attachments, and impair sensory information and motor output of the brain.

Equine hoof trimmers are brain surgeons. They change the sensory input to the brain, causing changes in motor output which lay down tracts for long term potentiation. Impaired heel first landing (balance) to the foot, by any peripheral loading device, increases the possibility of injury.

For all the chiropractic work in the world, you can’t get normal leg movement, normal motor cortex function, without normal heel first landing.

The joints must float in the soft tissue, even inside the hoof wall. The load of the limb must be borne by the bony column in order for the muscles to protect the joints, and for the muscle strength to act on the momentum and speed of movement with accuracy. The body must hang in the sling of the muscles supported by the limbs. This is how the horse evolved in response to gravity. Gravity is the largest sensory input factor to the sensory cortex and the drive for building motor cortex. Any information that goes to sensory cortex is translated to motor cortex to determine long term potentiation and survival. In quadrupeds, balance is four cornered. It takes a great deal of sensory stimulation and motor coordination to become bipedal. This is driven by gravity. The more a brain cell is stimulated the more it will increase its size and strengthen its connections and the more supporting cells will be produced (Melillo 2009). As gravity acts on the muscle, bone, tendon and ligament, both the body and brain are designed in concert.

Faulty information builds faulty conformation. Conformation is the current expression of genetic capability coupled with current (to the minute) experience (sensory stimulation). Poor hoof balance builds poor genetic expression, poor muscle development, poor joint design, resulting in pathology. Chiropractic can delay the pathology, but without normal input, the pathology will eventually be realized.

Muscle Attachments

The sensory tracts to the brain of the horse that indicate ground level, texture, temperature, depth are combined in the information presented from the heel of the foot, from the stretch of the extensor muscles of the leg, and from the stretch of the omohyodius and sternohyoidius muscles. These muscles do not achieve complete stretch without a heel first landing.

Joint Protection

Joints of the limb, and of the entire body, are not protected from muscle spasm and damage when the hoof lands without complete extension of the limb. The muscles of flexion are not able to support the load of the body weight, the forces of momentum and speed. Only the extensor muscles with combined tendon and ligament systems are designed to withstand these forces. When extensor muscles are weakened by non-use, shortening due to decreased motor cortex output, and decreased completeness of range of motion, joints become endangered.

The Hoof

Sensory input to the sensory cortex from the hoof is primarily located in the rear 1/3 of the sole (Bowker). Neurosensory perception: Evidence indicates so far that the sensory capabilities of the horse’s foot have exceeded our expectations in the horse’s ability to perceive the many and different stimuli within the environment, such as light touch and pressures with the frogs and soles much like our own feet. We believe that these sensory perceptions enable the horse to actively engage within its environment, as well as aid in the regulation of blood perfusion through the foot.

Hoof wall: The hoof wall is believed to be the primary support structure of the foot, and as a result traditional practices of hoof care have evolved to maintain such a support mechanism. Evidence is accumulating in our laboratory suggesting that the hoof wall is NOT the primary structure of weight bearing and should only have a secondary and/or minor role in support. (Bowker)

Miesner corpusles located in the rear sole and frog of the foot detect ground surface information, alerting the brain to regulate step, contralateral balance, gait, balance. Even in studies using balance plates to measure hoof balance and load, the surface of the plate itself affects the load the animal places on the limb and thus the area of the foot that contacts the plate.

When the foot is impaired due to poor foot balance, poor blood flow as evidenced by corns, calluses, abscesses, underrun heels, long toes, the judgments needed to determine where to place the limb. This results in chiropractic subluxations by definition.

Use It or Lose It

The sensory information delivered to the brain and spinal cord begins with conception, but the greatest burst of information from the surrounding environment is experienced at birth. The new born foal has a soft foot with soft exterior hoof wall that is unfit to bear any weight. Yet the foal stands, nurses and begins movement within minutes of birth. This alone demonstrates that the hoof wall structures are not weight bearing structures in and of themselves. The sensory information generated from sensory tracts already laid in the soft tissues of the foot determine how the animal will develop hoof shape, how the movement will dictate hoof shape and muscle function.

At birth gravitational forces along with friction begin to shape the foot, widen it and develop the soft tissues that surround the bones, P2 and P3, necessary for standing, balance and motion. Gravity is the only constant source of stimulation, and what will develop spinal tracts, sensory and motor cortex that will drive conformation. Every 20 seconds 500,000 nerves are either developed or die as a response to this system. Movement is what drives the foot to grow and develop. Horses that stand in stalls for even a portion of the day do not grow and change their foot structure as quickly as horses that are on pasture 24 hours a day. They do not develop as normal a hoof wall, sole, or lamina as horses out on terrain. Sensory input and blood flow are the keys to developing the foot of the young horse.

Normal Foot Conformation

Normal hoof conformation is determined by a trim that allows heel first landing.

Historically normal hoof had been defined by what was seen commonly. Yet what is commonly seen among horse foot populations is shaped by trimming and shoeing protocols, an environment designed to protect and comfort the human who owns the animal, rather than the animal who evolved in an environment with boundaries only defined by natural forces. The sensory input to the foot has changed.

Ongoing research is helping us to see what the “original” equine foot should be. How that foot was originally defined by gravity, activity, and movement.

What has been determined is that a foot with heel first landing must have sole at the “buttress” of the heel. The bar helps in the growth of the sole, and in the stability of the heel structures. Above the frog and bar lies the digital cushion, which is also made more functional by a bar that is of normal, vertical shape. Horses with compressed, contracted, corned heels will lead to heel pain, and move the landing forward on the foot. This reduces sensory input to the brain, resulting in poor heel development., narrowed frog, contracted heels, poor hoof tissue pH, poor hoof tissue repair, poor hoof tissue development. These horses land either mid-hoof or toe first.

The result of this leads to osteoporosis of the coffin bone, as evidenced in the work of Dr. Robert Bowker. Decreased sensory stimulation to the foot, resulting in improper use of the tissue, imbalance of the muscles that move the limb, results in decreased sensory load to the bone, tendon, ligament, and muscle, which result in decreased sensory input to brain structures and decreased motor output to the system. The horse develops muscle spasm and fatigue. It begins to show signals of central pattern generator malfunction as it attempts to compensate for flexor muscles that are not designed to hold against gravity. Extensor muscles, due to daily fatigue of stretch, begin to spasm and shorten. This over time changes the posture of the animal. This over time increases the potential for injury. There are other sensory influences to muscle function, but that is another lecture.

While farriers are brain surgeons, they cannot do it alone. Chiropractic cannot do it alone. The information from the environment that is designing the body must be correct. If the environmental influence of gravity is faulty, you must have a heel first landing. When the extensor muscles are functioning to their full potential then the joints are protected. They float in the soft tissue. Then you can adjust horses and make the miracle of the innate work. To help your chiropractic work make the animal more stable, hold adjustments and decrease injury during activities, you must have a heel first landing.

No hour of life is wasted that is spent in the saddle.  ~ Winston Churchill