In our last article, we discussed the exterior structures of the hoof. Today we will be discussing the internal structures of the hoof. There are two and a half bones inside the hoof: the Pedal bone, the Navicular bone and the bottom half of the Short Pastern bone.
Pedal Bone: This large bone inside the hoof capsule is known as the Pedal bone or Coffin bone. The pedal bone provides strength and stability to the hoof and acts as the framework to hold other structures in place. Surrounding the front wall of this bone is the very sensitive laminar corium which produces the intertubular horn of the hoof wall. The bone is covered in solar corium which produces the sole. At the back, the bone joins onto cartilage which forms a large portion of the back of the hoof. A great many tendons and ligaments attach to this bone and a network of blood vessels run around and through it.
Navicular Bone: Also known as the Distal Sesamoid bone. The navicular bone is not actually embedded in a tendon, but it sits just inside the back of the pedal bone and the deep digital flexor tendon passes over it. It prevents over-articulation of the joint of the pedal bone as well as maintaining a constant angle of insertion of the Deep Flexor Tendon into the back of the Pedal bone.
Short Pastern Bone: Also known as the Middle Phalanx, this short bone sits on top of the articulating joint of the pedal bone and underneath the long pastern bone. Only the bottom portion of this bone extends as far as the hoof capsule.
Digital Cushion: This sits just behind the pedal bone and above the frog. It plays a vital role in shock absorption. An improperly functioning foot, will find the digital cushion atrophying and becoming fatty as opposed to springy and the blood vessels within it will change limiting its ability to absorb shock. The shape and health of the digital cushion greatly influences the angle of the Pedal Bone. For example, a flat footed horse's pedal bone will lie flat instead of being tilted slightly and you will note that the digital cushions are severely atrophied.
Coriums: This is the vascular structure which manufactures the outer elements of the hoof capsule. For example, the solar corium produces the sole, the frog corium produces the frog.
Lateral Cartilage: The lateral cartilage is located both above and below the coronary band extending around the front, sides and back of the hoof. This cartilage provides resistance as the pedal bone descends during weight-bearing, regulating the amount of pressure applied to the coriums. They also help to suspend the pedal bone in the correct position.
The hoof is very heavily supplied with blood by five venous plexuses or veins.
Solar: Nourishes the horn producing corium that generates the sole,
Digital cushion: Blood vessels that run through the digital cushion,
Lateral cartilage: Supplies the cartilages with blood,
Lamellae: Nourishes the corium producing the intertubular horn of the hoof wall, and
Coronary: Supplies the coronary band with nutrients it needs to produce the hoof wall.