Saturday, Jan 30, 2010 - Forelimb anatomy

Vet Tip of the Day: Foot and Pastern Anatomy/Heel pain
Key Words: navicular, coffin, pastern
How well do you know your horse's anatomy? For the next week we will examine the forelimb, beginning from the ground up - when I am learning anatomy I find it helpful to read the anatomical description, look at a diagram, then close my eyes and visualize what I've just learned. It takes discipline and patience to do this, but if you make the effort you can piece by piece learn your horse from the inside out, and thereby understand and detect athletic injuries more quickly and acurately.

Today we will go from the ground to the fetlock. Beginning from the ground, within the hoof capsule lies the coffin bone (third phalanx, P3), the navicular bone, and about 1/2 of the short pastern bone (second phalanx, P2). From the coronary band, or hair line at the top of the hoof, to the first large joint, the fetlock, are the top 1/2 of the short pastern bone and the long pastern bone (first phalanx, P1).

The navicular bone sits nestled behind the joint between the coffin bone and the short pastern bone. The deep digital flexor tendon, which runs down the back of your horse's leg, attaches to P2 and P1, above and below the navicular bone, respectively. Therefore, as your horse moves his leg, this tendon slides up and down along the back of the navicular bone. There is a fluid filled sac, called a bursa, between the tendon and the navicular bone. If there are any irregularities on the surface of the navicular bone, this bursa becomes inflamed, which in turn can inflame the tendon. Over time this can result in the deposition of scar tissue, or adhesions, between the tendon, the bursa, and the navicular bone. This is one of the primary causes of heel pain in horses with "navicular syndrome". Poor hoof conformation and poor shoeing are the most common predisposing factors to the development of such heel pain.

OK, what are the bones from the ground to the fetlock? Close your eyes and imagine the flexor tendon sliding up and down over the navicular bone as your horse's foot flexes and extends. Go out and explain to 3 friends today what you now understand about the pain that arises when your horse has a diseased navicular bone.

(If you click on the diagram it will enlarge and you can scroll up and down to help see things more easily)

Your brain is no different than any other muscle in your body - it hurts at first to make it work, but after awhile it starts to feel great!