Follow the dysfunctional process

As we follow the dysfunctional process, the bars of the equine foot will reduce in height as their distal palmar section builds up more fibrocartilaginous material, becoming more prominent and encroaching on the wings of the distal phalanx. The proximal palmar aspect of the bar tends to roll under (on its proximal palmar aspect), causing the entire internal bar to migrate dorsally towards the toe.

These structural alignment changes mean that the digital cushion is forced to endure additional loading forces and extra weight from the upper body, aggravating the failed containment of its structure within the internal bars. A flow-on effect is the impaired vascular infusion to the digital cushion caused by the entrapment of the distal phalangeal artery against the imploding collateral distal cartilages, which reduces the size and biological function of the digital cushion’s tissues. 

The digital cushion's size reduction and alignment change compromise the limb's distal bones' descending arc. It breaks the axial alignment that influences the loading and rotational forces through the distal interphalangeal joint, thus instigating a forward migration of the hoof capsule.   

The palmar section of the equine foot’s loss of integrity dictates the changes seen in the shape of the external hoof capsule and its alignment with the distal joints of the limb. It also instigates podiatry problems such as underrun heels, medial-lateral flares, concave dorsal walls, sole growth and misalignment issues, and extruded heel bulbs.

Regarding the timeline of structural dysfunction, the digital cushion is the next in line to experience the downward spiral of structural integrity. The developing characteristics are a shape change and impairment of its supporting role. When the internal bar no longer maintains its structural alignment, the digital cushion wanes to the additional forces imposed on it. It is compelled to change its shape and alignment, thus reducing its supporting capacity.

The healthy attributes of the digital cushion lie in a triangular wedge-shaped structure that looks like the head of a cauliflower, tightly formed with interlocking cells that cooperatively support the animal's body weight and counteract the forces of ground impact. As the digital cushion turns into a structure of individual layers of elongated tissue, it becomes unable to maintain its overall wedge shape, severely reducing its supporting capacity. The ongoing structural and biological breakdown instigates a splitting of the distal section, and we will find that the areas below the heel-bulb alignment diminish in size. The proximal section of the digital cushion extends backwards, forcing the remodelling of the heel bulbs, which become extended.

Due to the remodelling of the palmar section of the equine foot, the internal bars and digital cushion are unable to maintain correct anatomical alignment and acceptable biological function, resulting in the animal’s weight and descending forces being transferred instead to other internal structures of the foot; such as the deep digital flexor tendon, navicular bone and bursa, distal sesamoidean impar ligament, collateral ligaments and distal cartilages, changing the internal relationship between the hoof capsule and the bony structures, and affecting the animal’s orthopaedic balance.