The totally underrated Digital Cushion: a horse owner’s guide

 

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.

palmer hoof digital cushion

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.

Venogram of the digit

 

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.

 

 

One thought on “The totally underrated Digital Cushion: a horse owner’s guide”

  1. Great post, Elizabeth. I too consider the digital cushion to be an important and under-rated structure. One reason for this, I think, is because it doesn’t show up as a well-defined structure in a normal radiograph.

    Things really changed for me back in the 1990s when Allie Hayes (of http://horsescience.com) started making her freeze-dried hoof models. The first thing I noticed was that if you put several of them side by side, the shape and size and location of the digital cushion was different, even if the shape and size of the feet was similar. Now we can see the same thing on MRI scans of living horses.

    I don’t know if you’ve seen Dr Pollitt’s new book, The Illustrated Horse’s Foot, but he documented the growth of one of a foal’s feet at weekly intervals to show the shape change. I’d love to see someone do periodic radiographs of the same horse’s same foot over years and see where and how and if the dc changed shape vs how the overall foot shape and size changed.

    I go to so many lectures on hoof-related subjects, and yet the digital cushion is rarely mentioned in describing hoof balance or health. When and if the digital cushion can be restored to a healthier location in the foot, what is the affect of age and how long it has been smooshed out the heel bulbs? What is the effect of having a portion DC under the navicular zone–or, of not having it there?

    Why don’t more people, other than barefoot advocates who believe they can “see” the digital cushion without the help of any diagnostic imaging, focus on its health? Why isn’t there a digital cushion biopsy technique to analyze the fat/collagen structure (or simply the level of myxoid tissue) present? And is the myxoid tissue always in the same area, as Dr Bowker describes when he talks about the medial-lateral threads spanning the back of the foot? Would a horse develop the myxoid tissue as a response to weightbearing and exercise or is it born with it? Are all horses born with the same ratios in their DCs?

    So many questions, but I’m so glad you are asking them too.

    Thanks for recommending the Epona videos, they are great!

    And so are you! Onward!

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