Whether you know it or not, your horse has experienced foot-related pain during his or her athletic career. We all know that horse’s feet, especially the front feet, are vulnerable to many external and internal forces. In short, it’s where the rubber meets the road. Fortunately, we can control how these forces act on the foot with a careful look at the relationship between the skeleton of the lower limb and the hoof.
How do you know your horse’s feet are causing a problem for you or your horse? Most obviously when your horse is lame and the source of the lameness is isolated to the foot with diagnostic nerve blocks. Does your horse lose shoes for no apparent reason? Does your horse trip or stumble periodically? How about forging? All of these are reasons why your horse's hoof needs careful attention.
Throughout this discussion, I will avoid using two words. Balance and Support.
Balance and support are ideals sought by everyone for everything. The problem is, when it comes to caring for a horse’s foot, nobody knows exactly what that is. So I’m going to use specific measurements using radiographs of the horse’s foot to guide the process of trimming and shoeing your horse with information that is reliable and easily obtained.
Let’s start with a few definitions:
Sole depth: measured from the tip of the coffin bone to the bearing surface of the foot (the ground). Ideal sole depth is 15 mm give or take a couple mm. Too little sole depth, the foot is vulnerable to bruising. Too much sole depth and the foot is likely too long causing tripping, lameness and other problems.
Heel height: measured from the back of the coffin bone to the bearing surface of the foot. Ideal heel height is always a measurement higher than sole depth. If it is not, there is a negative coffin bone angle (more about that later) and if there is less than 10 mm of heel height, the digital cushion is possibly damaged. We also measure separate heel height for the medial (inside) and lateral (outside) heels. More about this later.
Negative coffin bone angle: ideally, the coffin bone has a slight upward angle compared to the hoof (usually 2-5 degrees). A negative coffin bone angle is usually caused by inadequate heel height. The negative coffin bone angle in the example below is 2.3 degrees.
Breakover: the most controversial measurement of the hoof, this is a measurement of how far forward the toe is. This breakover defines when the foot starts to breakover with each step. This is critical for horses that forge or pull shoes, but it is even more critical for horses with problems in the coffin joint and navicular region. Although a rapid breakover is ideal in most cases, in some cases if it is too soon it can exacerbate an existing problem in the suspensory ligament or superficial digital flexor tendon. As a respected farrier told me, "You can shoe for navicular or you can shoe for suspensories. Take your pick".
Breakover is measured one of two ways. The first way is to determine the center of articulation of the coffin joint then dropping a vertical line down to the ground surface. With this measurement, the ideal is to have as much foot ahead of this line as behind it. The second way, and my preference, is to drop a vertical line down from the tip of the coffin bone and determine existing or ideal breakover by measuring from this point forward to the front of the toe or shoe. The ideal breakover with this measurement is between 0 and 15 mm ahead of the tip of the frog. The breakover distance in this radiograph is represented by the red line.
Now that we have established some definitions for measuring various aspects of the hoof, we'll take a look at some issues you may be experiencing with your horse in our next installment. Stay tuned!