What's Inside the Equine Digital Cushion?
Your horse’s hooves are complex structures that contain several important bone and soft tissue structures, all protected by the thick, elastic digital cushion. Veterinarians know this important piece of anatomy, located above in the rear part of the hoof, absorbs energy and forces placed on the hoof, but there’s much about the digital cushion that remains unclear.

Recently, Babak Faramarzi, DVM, CVA, MSc, PhD, and colleagues conducted a study to gain a better understanding of the digital cushion’s connective, nervous, and adipose (fat) tissues, as well as vascular components. He presented the results at the 2016 American Association of Equine Practitioners Convention, held Dec. 3-7 in Orlando, Florida.

“Previous studies are inconsistent, with some claiming that digital cushion (DC) is primarily a fat pad,” said Faramarzi, an associate professor at the Western University of Health Sciences College of Veterinary Medicine, in Pomona, California. “Collectively, these studies represent disagreement about the architecture of the DC. Our results showed that the composition/structure is far more complicated.”

He recently collected samples from the hooves of 24 clinically sound Quarter Horses euthanized for reasons unrelated to the study. They examined samples from four regions of the digital cushion—axial-proximal (top center), axial-distal (bottom center), abaxial-lateral (outer edge), and abaxial-medial (inner edge)—via light microscopy.

Faramarzi said the team found that the axial-distal region had significantly more collagen (a type of protein found in connective tissues) and fewer elastic fibers than the axial-proximal and abaxial regions.

“The presence of a moderate to large amount of elastic fiber profiles in the DC, with its high resilience, may allow the elastic fibers to support the tensile strength of collagen bundles,” he explained. “Elastic fiber-rich dynamic tissues are, therefore, able to deform and store energy under normal physiological loads and use this energy to drive recoil back to a resting state.

Additionally, there were about four times as many nerve bundles in the axial-proximal region than in the axial distal region, he said, indicating there are more nerves closer to the horse’s limb than there are near the hoof’s sole.

“This study, for the first time, characterized the architecture of different regions of the DC,” Faramarzi said. “Such regional structural differences of the DC are presumably related to the different functional properties of those regions.”

But would the results be different in horses with poor hoof quality or a compressed digital cushion?

“I’ve been an equine practitioner for more than 20 years—my clinical experience tells me ‘yes,’ ” Faramarzi said. “However, as a scientist, I should say we need more research.

“The results of this study are focused on mature/older Quarter Horses with no known hoof pathology; whether the composition of the DC is different in horses with different conformations or suffering from hoof pathologies such as low heels or navicular syndrome warrant further research,” he said. “Also, more research is needed to investigate the influence of age, breed, exercise, shoeing/trimming, as well as environmental factors.”

Faramarzi said he hopes this study’s results encourage additional research on the topic.

“It is said that up to 80% of musculoskeletal injuries originates from hoof/foot problems,” he said. “That is a huge impact; however, our knowledge of hoof function is limited. One reason is difficulty of such research. There are lots of variations among horse feet, and it makes scientific studies even harder. And, more importantly, available funding for equine podiatry (foot diseases) studies is very limited. Personally, I believe close collaboration among veterinarians, farriers, trainers, as well as equine industry and horse owners is critical.”