Firstly, if the stance of a horse has correct skeletal alignment it enables the equine to rest with the least muscular activity, which reduces the toxin build-up in the muscles, enabling the horse to rest properly. A sign of misalignment is a horse that is transferring weight from one hind leg to the other, standing with both limbs under the body and with tension in the back. The connecting tissues and muscles have to compensate for the misalignment of the limb, when the joints of the skeleton are not loading the horse's body weight through the centre of each joint.

Function

Let us look at the function of the horse's hind end.

This part of the animal is the engine that drives the horse forward with, at times, explosive power. The hocks transmit that power from the muscles of the back to the feet that then propel the horse forward. The hind end is also part of the horse's defense, as when pursued they can kick violently backwards when in full flight.

The hind limb has three phases to the stride when working in a balanced way:

Phase One

The flight through the air and the landing phase. Heel first landing absorbs kinetic energy. The foot lands to the outside of the front feet. This can be seen in a more pronounced way the faster the horse moves. It happens because the condyles of the hock joint run medially laterally from the proximal to the distal aspect of the hock and is nature's way of helping to prevent impact injuries to the front limbs, such as over reaching.

Phase Two

The weight bearing phase. This is when the limb is vertical and the foot flat to the ground.

Phase Three

The power or driving phase. From the vertical position back is the driving part of the stride using the toe to transmit the muscular power from the top of the limb through the hock to the ground. When the limb is misaligned, this part of the stride is reduced in direct relation to the amount of distortion in the toe. When the limbs are in balance, however, the third phase of the stride is a very efficient way to transmit energy. However, if I am correct and an inefficient hind end makes a horse need to assist the forward propulsion causing the front legs to pull, the weight they are asked to carry on the front limbs is increased, making the horse heavy on the forehand when being ridden.

How to prove my theory? Mathematics I thought! So I asked an engineer to help. My theory was that if a horse distributes its weight by 60% on the front limbs and by 40% on the hind limbs when standing with its legs straight, if the hind limbs move under the horses's body this increases the weight carried by the front legs.

Angle Degrees Weight on Front Limbs % Weight on Hind Limbs %

0 60.00 40.00

1 59.29 40.71

2 58.55 41.45

3 57.49 42.21

4 56.99 43.01

5 56.16 43.84

6 55.30 47.70

7 54.40 45.60

8 53.46 46.54

9 52.47 47.53

10 51.44 48.56

The degree angles indicate the forward movement of the leg from the vertical position

This was not the case, but I shall leave the figures in as they may prove to be useful for laminitis, which when I thought about it, was obvious as it is the typical stance of a laminitic. Back to the drawing board and more observations of the horse! This proved to be vital because I had been concentrating on one end ? the very thing I was trying to avoid!

With renewed observation, I noted that a laminitic has its legs held out in front, but with misalignment of the hind limbs in the non-laminitic horse, the front legs go back under the body.

Time for more detailed mathematics!

Typical Stance of Unbalanced Horse

Typical Stance of Unbalanced Horse 

Figure 1.1 Normal Standing

Figure 1.1 Normal Standing

Figure 1.2 Front Limb Lameness

Figure 1.2 Front Limb Lameness

Figure 1.3 On the Point of Moveing

Figure 1.3 On the Point of Moveing 

Figure 1.4 Foreces on the Front Feet

Figure 1.4 Foreces on the Front Feet

Forces on the Front Limbs as a result of Hind Limb Misalignment

Normally the horse stands as in Figure 1.1 with approximately 60% of its weight resting on the front feet and 40% on the hind. When the horse has front foot lameness the rear legs lean backwards in order to take more of its weight. This is shown in Figure 1.2. In order to begin forward motion the horse leans its front legs forward so as to shift the rear legs into a forward leaning pushing position. In Figure 1.3 we see the legs just as the horse is about to pull its rear legs forward by applying a forward force with the front legs. The force exerted by the front hoofs has a vertical and a horizontal component. The vertical is always present in healthy animals and produces little stress on the feet. The horizontal component, however, pulls backwards on the foot. This is stressful and the components are shown in Figure 1.4.

The size of the horizontal component depends on the angle of the leg. Table 1 shows how it increases with the angle of the leg. It is given as a percentage of the horses weight which rests on the front legs (assume 60%) and in Newton's assuming a horse weight of 500kg.

Leg angle ß Horizontal Component % Horizontal Component (N)/Hoof

1 1.7 25

3 5.2 76

5 8.7 128

7 15.6 229

9 19.1 281

11 22.5 331

13 25.9 381

As a farrier, what do I look for and how do I deal with the problems I find when trying to achieve increased length in phase three of the stride?

When working with a Veterinary Surgeon, x-rays are a must as the position of the distal border of PIII can be found and breakover placed accurately at 3mm in front on a small foot and up to 5mm on a large foot. It also assists in positioning PI, PII and PIII so that the weight is borne through the centre of each joint. But when working without x-rays, I want the limb to be vertical or back behind the vertical when the horse is standing relaxed (not being made to stand square). Standing back from the horse, I imagine a line dropping down from the last point of the hind quarters and I want the hock and the fetlock to be touching the imaginary line, or behind it.

Near fore and near hind trimmed - off fore and off hind untrimmed

I then walk the horse to observe footfall and length of stride behind the vertical (the power part of the stride). I look at the wear pattern on the shoe, position of breakover and condition of the frog (whether atrophied, functional or prolapsed). Looking from the front I determine whether the feet are straight or point out laterally, indicating distortion or elongated toe which sometimes gives the appearance of cow hocks. These factors will determine how I prepare the feet and shoe it if required.

Trimming

I locate the widest part of the foot, trim back to the widest part of the frog, removing chalky exfoliating tissue and leaving the frog intact. I remove any wall above the live sole at the toe and create a breakover, which, according to Dr Barbara Page, is closer to the tip of PIII behind than it is in front. I then observe the horse both standing and walking ensuring the horse lands just heel first and stands with vertical limbs.

After this assessment, I decide on the shoeing procedure that will enable me to achieve heel first landing and increased length in the power phase of the stride. I use Natural Balance shoes for this procedure. I often select a NBS front shoe as it gives me a wider toe that is easier to fit to a distorted foot for accurate placement of breakover. I also use graduated pads and impression material to reinstate phalangial alignment. Without x-rays, I have to assume this is achieved when the horse regains heel first landing.

Conclusion

If lameness has no defined cause, I have found it helpful to shoe the horse behind with pads if necessary and reassess the horse and many times the problem has then become apparent. When hind limb alignment is corrected I have observed dramatic effects on the horse?s back. Physiotherapy, acupuncture or chiropractic care is more often than not needed to adjust the back during the treatment period. Muscles working more efficiently also change the shape of the back and the saddle may well have to be adjusted, and possibly more than once, during this period of realignment.

So in conclusion, when Veterinary Surgeons and Farriers vet, trim or shoe a horse I would stress the importance, to the horse?s well being, of more attention being paid to the alignment of the hind quarters.

Clive Meers Rainger RSS Bll CNBF CLS

August 2009

Acknowledgements

The Household Cavalry for my basic training. My partner who looks after the business when I am having a jolly!

David Nicholls, my constant companion and mentor and from the other side of the pond: Gene Ovnicek, Dr Barbara Page, Dr Robert Bowker,Dr Joyce Harmen, Dr Kerry Ridgeway, Mark Plumlee and all the interesting people I have had the pleasure to meet and work with on my trips to the States.