The digital cushion is a major component of the circulation and shock dissipation apparatus of the horse’s digit. It is a elastic, wedge shaped mass composed of a fibrous fatty tissue that has the consistency varying between your earlobe and nose depending on it’s health. Ideally, the digital cushion takes up the majority of the rear 1/2 of the hoof. It’s nestled underneath the deep flexor tendon, between the lateral cartilages, and above the frog. The DC can be felt by pressing between the bulbs of the heel.
The DC has sheet like ligaments that stretch from one lateral cartilage to the one opposite, allowing for independent movement of the sides of the foot. The digital tarus, part of the DC, originates from the underside of the coffin bone and deep digital flexor tendon and sends bands of fibrous tissue toward the heels creating a a biologic lattice for the vasculature of the back half of the foot. There are also a series of trampoline-like ligaments traversing the inner surface of the frog, facilitating it’s expansion and contraction.
Horses have many ways to dissipate the concussion of moving at speed. One way is by hemo-dynamic shock absorption in which the digital cushion plays an integral part. Let me explain:
During the swing phase of stride, blood is pulled into the extremities via centrifugal force. Upon the hoof landing, the fetlock descends. This drop causes the veins to close, trapping the blood within the hoof and dissipating shock like a waterbed. Much of this trapped blood is in the matrix of tiny veins and capillaries running amongst the sub structures of the DC. As the horse passes over the hoof, the fetlock rises and the blood-way is open. This built up pressure then shoots the de-oxygenated blood back up the leg, returned to the body and heart.
It is important for the horseman to know that there is a wide range of variability when comparing DC between good and weaker footed horses. In a strong hoof, the ligaments of the DC are much thicker and the digital tarsus will have numerous fibrous connections . The reasons for this are thought to be due to the presence of a highly adaptable myxoid tissue in the region. Myxoid tissue is very adaptable and can become fibrous or cartilage. It is thought that the environment and how the foot is trimmed and/or shod can contribute to the makings of a robust foot.
Util recently, most discussions on hoof lameness were limited to deterioration or injury to the navicular bone, coffin bone, the deep flexor tendon, the navicular bursa, distal sesmodian (collateral) ligaments or the coffin joint capsule itself.
It is my belief that these structures are often damaged due to lack of a properly functioning digital cushion. Further, I believe that much of the objective of best farriery practices is to be aware of the health of this underrated structure. In my practical experience I have come to believe that digital cushion is very adaptable, even in mature horses or ones with already compromised hooves, Horses that are well managed with plenty of exercise over varied terrain and shod or trimmed in a balanced manner will tend to have a more fibrous DC than horses that are kept up and not shod or trimmed well.
For more information on the Digital Cushion, I would like to recommend Epona TV’s 6 part series featuring Dr. Bowker.