Uniform Sole Thickness

 

M.T. Savoldi, G.F. Rosenberg

 

During 28 years as the resident farrier at California State Polytechnic University at Pomona I found that by trimming to “uniform sole thickness” the true foot reveals itself such that form and function are optimal regardless of breed or confirmation. Horses go better and stay better. Uniform sole thickness (UST) defines the plane of the hoof capsule. That is to say, the sole, at each point of connection to the hoof wall is of equal thickness from heel to toe. When uniform sole thickness is not maintained adverse changes occur. My work has shown these results to be consistent.

 

In this article and a series of articles to follow I will present a series of photos documenting the progressive stages of a dissection of the horses hoof. This hoof is representative of the thousands of feet I have dissected. It serves to illustrate the principals of trimming to a uniform sole thickness. In this first article I will focus on the heels.

 

There seems to be general agreement as to toe length. Everyone’s opinion will be slightly different, but overall, a group of professional farriers will look at a foot and arrive at some consensus with regard to toe length. However, with regard to length of heel there is wide disagreement. What I have found to be the case and will put fourth herein is that in order to establish uniform sole thickness the heels should be taken down to the junction of dead and live tissue in similar fashion to that treatment normally given to the toe area.. Put simply, it doesn’t matter how far down or how far back you take the toe if you leave too much heel. Hopefully the following photos will help to illustrate this point.

Fig 1. From this angle it is difficult to determine much about this foot. There appears to be a dish in the toe which might indicate an excess of toe length. Traditionally, it has been thought that when the angle of the toe, the angle of the heel and the angle of the first, second and third phalanx (PI- PIII) line up the foot is in correct trim. It appears as though the toe and the heel angle line up pretty well on this foot.

Fig. 2. A window into the foot reveals three layers of tissue: Dead, or necrotic tissue which appears white and chalky; above which there is healthy living sole, yellowish in color and more waxy in appearance; and a final layer of sensitive lamina which is reddish in color. Here it begins to become apparent that although our angles appear to be “correct” there is an excess of heel on this foot.

Fig. 3. Removing the first layer of necrotic tissue reveals a layer of living, healthy sole. With this tissue now removed it is hopefully more apparent that there is excess wall length in the heel below the level of the live sole. This excess heel dramatically changes the mechanics of the foot.

Fig. 4. In this final frame the wall has been trimmed parallel to and at the level of the live sole, to uniform sole thickness leaving the excess wall length in the heel. It should now be quite apparent that contrary to what might have been initially obvious the length in this foot is not so much in the toe as it is in the heel. Although the hoof has been trimmed to uniform sole thickness, the plane of the hoof capsule remains elevated by the excess ofwall length in the heel area.  Unless this excess length is removed body weight will continually cause movement of tissue creating flares and possibly causing the sole to drop.

 

 

 

This is the second in a series of three articles that attempt to convey the importance of trimming to uniform sole thickness (UST). The photos show the progressive dissection of the hoof capsule to illustrate pathological changes which occur when UST is not established and maintained. It is my hope that this series of photos depicting the progressive stages of the dissection of the hoof will clarify the importance of establishing UST. This article will illustrate three points: (1) Horses are well-served by establishing and maintaining UST. (2) The petal bone (Plll) moves within the hoof capsule creating sole flexion, when there is excess hoof wall the sole deform. In such that the Plll bone “seeks out” the level of the horizon. (3) When UST is not established and maintained the hoof capsule and the sole distorts, and over time Plll remodels.

In the first article we demonstrated that although the apparent length of wall in this hoof is in the toe area a window into the hoof wall revealed that in reality the majority of length was in the heel.

Fig. 1.  This first frame (the same frame as the final image of the first article) shows a hoof that has been trimmed to UST. I have left the original length of wall in the heel area. I hope it is apparent that the heels are too long. Also, notice the compression rings within the hoof wall of the toe, distortion in the toe area show flattening and flaring of the toe on the hoof capsule.

Fig. 2. In this second frame I have removed the distal portion of the hoof wall. Notice that the sole has uniform thickness (aside from the excess length of wall in the heel that I left for illustration). The unsound nature of the original trim should now begin to be apparent. Imagine this hoof under load - something will have to give, either the heels are going to collapse or the sole will have to bend or both. How the hoof reacts to excess length of wall depends on a variety of factors including confirmation, the size of the animal and the way in which the animal moves.

Also, in comparing Fig. 2 to Fig. 1, it should now be apparent that the toe flare is actually caused by excess wall length in the heels. Again, imagine this hoof under load, each time the horse takes a step Plll is “jammed” forward and downward causing the sole to flatten and the toe to flare out. When a hoof is trimmed to UST and regular shoeing intervals are maintained there are no toe flares to speak of.

 

Fig. 3. This frame illustrates several points. First, notice the shape of the sole. There is a flattening in the toe area.  The heels have also been pushed up. The result is that the Plll is essentially being suspended between these points causing an unnatural curvature to the sole.

Fig. 4. In this final frame the excess length of wall in the heel area has been removed. The hoof capsule is now on the same plane as the horizon. Observe the space between the heel and the ground surface. This is distortion in the heel. The sole is in an upward bend. One of the many advantages to UST is that distortion of the sole can be easily recognized. Our goal for trimming to UST is to remove distortion to the sole. When shoeing for distortion of this type place a level shoe on the foot such that the heels float and let the sole level to the shoe. The sole will level to the shoe very quickly, how quickly will depend on several factors including moisture content of the hoof, and the severity of the distortion. Leave the frog in tact to provide sole support and assist with blood circulation.   

 

 

In the previous two articles in this series we demonstrated how to analyze a hoof trimmed to uniform sole thickness (UST). In this article we will demonstrate pathology based on the plane of the bone that arises in a foot not trimmed to UST. If a hoof is trimmed other than to UST the sole and the pedal bone (PIII) will distort. The sole will flatten and PIII will remodel.

The photographs in this article show the final stages of dissection. The hoof depicted shows the result of not trimming to UST. PIII has remodeled and the soundness of the animal has been compromised.

Fig. 1 This frame shows a foot which has had the hoof wall removed. The toe area of PIII is pushing into the sole causing the sole to sag and the bone to degenerate. Take a second to think about the dynamics which would cause this type of pathology. Trimming with excess length of wall in the heel positions the bone for this type of remodeling For illustration; imagine a human foot within a cowboy boot, the raised heel causes internal pressure in the toe and contributing effects to the muscles and ligaments.

Fig. 2 This frame depicts the same hoof from a slightly higher angle focusing on the toe. PIII has remodeled such that the leading edge of the bone has been pushed upward, (lipped.) This type of lipping has two possible causes: excess of wall length in the heel or possibly a very steep arch under the palmer process, or both. In both cases trimming to UST will minimize the lipping.

 

Fig. 3 Looking down on the proximal surface of the sole. Note the darkened area in the toe. This is sole bruising. Clinical signs show that PIII is weight-bearing in the toe in this foot. The discoloration is from internal pressure of PIII and nerve damage. Note: this sole soreness is a result of downward movement of PIII in the toe as opposed to pressure resulting from the shoe or ground surface.

 

 

Fig. 4 Removing the dermis to exposes the solar surface of PIII we can see where PIII has flattened, degenerated and is loosing vertical depth. Also, note the lipping in the toe.

 

This case is typical, but not by any means a severe example of the distortion to PIII that occurs when a hoof is not trimmed to UST. If a hoof is continually trimmed such that UST is not maintained, the forces on PIII will cause remodeling. We know that the plane of the hoof capsule is set by trimming to UST, but the plane of PIII is defined by the angles of the sole. The sole seeks to be on a plane with the horizon (the level ground surface). Because the angle of PIII is dictated by the angles of the sole rarely will PIII be level with the horizon, however we as farriers can best promote hoof heath by understanding and trimming to UST such that the angle of PIII, and subsequently the entire bone column is normalized.

 

In conclusion, we as farriers need to learn to understand and accept what the foot is offering and learn to work within the parameters of what is offered and not attempt to dictate what we believe the ideal foot to be in order to improve, develop and maintain a healthy foot.