Anatomy can often seem a bit overwhelming and be a pretty dry subject, but it would be impossible to understand the effects of different trimming and shoeing methods on the functionality of the hoof without learning it….sooooo….let’s begin!
There are three bones inside the hoof capsule, from the ground up they are as follows: coffin bone, navicular bone, and the distal end of the short pastern bone—these three bones also make up the joint known as the coffin joint.
Moving up the leg, the next bone is the long pastern bone; where the proximal end of the short pastern bone and distal end of the long pastern bone meet is known as the pastern joint (if you don’t know already...distal is a directional term meaning towards the foot of the limb and proximal is an directional term meaning towards the top of the limb).
Moving up the leg again, the next bones are the cannon bone and the two sesamoid bones; these three bones plus the proximal end of the long pastern bone make up the fetlock joint.
Woohoo!...that’s it for bones and joints in the lower leg...not so bad, right?!
What can sometimes get confusing with bones is having many names for the same bone; below are some other common names for some of the bones of the lower limbs:
Coffin Bone - Pedal Bone, Distal Phalanx, P3
Short Pastern Bone - Second Phalanx, P2
Long Pastern Bone - First Phalanx, P1
Navicular Bone - Distal Sesamoid Bone
Let’s go a bit deeper and learn about how the joints of the lower limbs work!...
All of the joints in the lower limb are hinge-joints, meaning the joint movement is one of rotation around a single axis—forward (extension) and backward (flexion). If you have any trouble understanding a hinge joint, just go to your nearest door. The door’s hinge only allows the door to open and close, it does not allow the door to move up and down or rotate. The fetlock joint is the most stable hinge joint of the lower limb as the cannon bone and long pastern bone are locked in place by a central tongue and groove; making it an extremely stable joint capable of handling transmitting the muscle power of the upper limb to the foot . The pastern joint and coffin joint have some possibility of slipping from side to side which allows them to accommodate for variations in terrain. The side-to-side movement of the bones within each joint is restrained by ligaments. Ligaments are soft-tissue structures that connects bones to other bones. I won’t go into all of the ligaments within the lower limb here, but just remember this basic function for later...perhaps you are already starting to get an idea of how the balance of trim/shoeing job could affect these joints and their supporting ligaments?
The last thing we will go over in this blog are the tendons of the lower limbs. Tendons are soft-tissue structures which attach muscle to bone. Flexor tendons move the limb backward and extensor tendons move the limb forward. The common digital extensor tendon runs down the front of the limb and connects to the extensor process of the coffin bone. A “process” is any extension of bone extending from the main body of the bone, so the extensor process of the coffin bone is simply the point located at the top of the bone.
There is also a lateral digital extensor tendon which connects to the long pastern bone. The superficial digital flexor tendon runs down the back of the leg and connects to the long pastern and short pastern. The deep digital flexor tendon runs down the back of the leg all the way down under the navicular bone and connects to the coffin bone.
If you are worried you won’t remember everything about these tendons, that’s okay!...the key will be remembering their basic function and location, so you can visualize and contemplate how the balance of different trimming/shoeing jobs could impact them.
Phew!...That covers our first layer of anatomy. The next blog will start taking us into more of the anatomy that lies within the hoof capsule and start to reveal how the hoof grows as we begin to build our own imaginary hoof piece by piece.
***All photos courtesy of Cheryl Henderson—The Oregon School of Natural Hoof Care***
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