Hoof Pastern Axis- By Tom Knox DWCF

Definition:
This is often a good topic of debate amongst farriers, owners and vets. So you have just bought your Thoroughbred horse from a trainer, it has retired from racing and needs a good home. If you are sensible you will have had it vetted and everything seems ok but a comment has been made about its feet. The vet says the Hoof Pastern Axis (HPA) is broken back but with good farriery this can be rectified. Not always so, I'm afraid. Below are some examples of good HPA's.

They might not be ideal angles, but they all have correct HPA. When we talk about broken back or broken forward HPA this means there is a deviation in the normally straight line through the phalangeal bones from the fetlock through to the distal phalanx or coffin bone. Viewed from the medial or lateral sides here are examples of broken back, normal and broken forward HPA.

Now, in the case of diagram A the problem comes when the horse is brought home and is being shod. There it is with typical thoroughbred feet (not an awful lot of hoof wall to play with) and the dialogue goes " I was told with good farriery this could be corrected."

If it is just a build up of toe which makes the angle look broken back, just rasping the toe off will resume a reasonable HPA. If this is kept up there will be no more problems in the future. However, if the phalangeal bones are not in alignment, no amount of reshaping will bring them back in line. It will only be a cosmetic correction. Therefore the articular surfaces will be operating on their limits and pain or ossification will result (ringbone).

So, its not correcting itself, does this mean your farrier is not a good one? No, not necessarily. It might not be possible to correct. Unfortunately there is sometimes a lack of understanding regarding what is possible and what is not in the world of farriery to those professions who are only theoretical in their understanding and not practical and experienced

With a broken forward HPA, diagram C, the obvious thing is to cut down the heels. This is ok if the flexor tendons are long enough to allow it. Sometimes the shape of the hoof will give us a clue as to whether this is possible, a really A shaped foot often means the tendon is already tight. Cutting the heels down would cause tension in the deep digital flexor tendon resulting in a possible muscular spasm, exacerbating the problem. What you see sometimes is the toe broken off especially in yearlings, which will make the foot look more upright. With trimming this normally corrects itself.

Shoeing -
Bad conformation with over sloping pasterns, or feet that are too long at the toe are contributory factors. Faulty action can occur at the walk or trot. It is commonly found in the short backed long legged horses or horses that go wide behind. Also in the situation where the front feet are under the body e.g. Camped in front, or Sickle hocks.

If X-Rays show misalignment or broken back HPA shoeing can help a lot. The toe of the shoe can be set under the foot and either quarter clips or no clips and a rolled toe can be used. This eases the breakover and reduces tension on the flexor tendons. There are some "natural balance" shoes, which are available to help with these problems.

Heels should be kept long if possible again to support the heels and the back of the leg, see diagram.

Broken forward HPA happens mostly in young stock, very often in one foot but sometimes in both. The bones grow faster than the tendons resulting in a geometrical imbalance, resulting in upright or boxy feet.

Calcium supplements often giving to youngsters can make this situation worse, so can over feeding. Cutting the feed along with reducing heels, a toe extension or swan neck shoe can possibly help, but in my experience the only really successful procedure is an operation to lengthen the deep digital flexor tendon check ligament. This is clearly a procedure to be discussed with the vet and your bank manager!

Author - Tom Knox DWCF