New Developments Using the Four Point Concept

2001 - 14th Annual Bluegrass Laminitis Symposium Notes

New Developments Using the Four Point Concept

Written and presented January 2001 by R.F. (Ric) Redden, DVM

The strength of the four point trim concept continues to grow as I find new ways to apply the magic “pivot point” to the foot. This concept has the ability to transfer load and effect the tension in the suspensory/tendons of the equine digit, which appears to be directly related to the reperfusion of compromised growth centers. Reperfusing these vital growth centers greatly enhances the genetically programmed healing response of the foot.

Many people ask, “How does this method differ from traditional shoeing?” and “How do other versions of the four-point method differ?” The answers to these questions are as varied as the number of farriers using the four-point trim, but the basic formula remains the same.

Traditional shoeing is basically designed to protect the foot while offering little or no mechanical aid to enhance perfusion of the sole corium and laminae. It also fails to attenuate the tension of the deep digital flexor (DDF) tendon as it courses over the navicular bone.

Today’s definition of traditional shoeing can be traced back a couple of hundred years at best. Do you ever wonder, “What was considered ‘traditional’ before this?” Shoes worn by horses throughout Europe and Scandinavian countries hundreds of years ago are displayed at teaching institutions and museums, while thousands of others are in storage. Most differ greatly from the traditional shoe of today or even of the shoes that made their way into the first few books written on the subject.

I challenge those individuals who decry the four-point concept as not being “traditional”. This concept is actually so old that it is now new again. Hundreds of years ago, horses wore shoes designed to enhance the blood flow to the foot; and therefore, aid natural healing. These shoes were used well before present day shoeing standards were altered by more recent writings. It would be interesting to know when and how the farriers of Columbus’ era discovered the strong influence of placing the breakover well behind the apex of PIII. Obviously there were no x-ray machines at that time, so the only way to discover the location of the bone in relation to the shoe would have been to cut the foot and shoe down the sagital plane. I am certain that some who were inspired to move forward did just that.

How does the four-point concept work to enhance the healing environment of the foot? Apparently a very delicate equilibrium exists between the flexor tendons and suspensory structures of the foot. When in harmony, these groups act as a unit with a multi-complex function.

The laminae, especially the anterior two-thirds, are a direct antagonist of the DDF tendon. The extensor tendon that attaches to the most proximal prominence of PIII is also an antagonist of the DDF, but it is considered the weaker of the two. Furthermore, the coffin bone is supported within the capsule by the laminae, chondral collateral ligaments, impar ligament, the sole corium, sensitive frog and digital cushion.

The laminae along the posterior half of the foot are also attached to the flexible ungual cartilage. Apparently, this cartilage is a very forgiving structure that significantly prevents laminae sheering in most laminitis cases. The entire system rests in the sling of the DDF that is multi-functional itself.

For the sake of discussion, lets simplify the biomechanics of the digit and develop a meaningful and useful alertness for the load sensors and their caution lights. Lets assume a large majority of the horse’s weight is resting in the sling of the DDF. This weight extends through the tendon, down the cannon bone and across the proximal sesamoids. It makes a turn and continues down the back of the pastern, followed by another abrupt turn under the navicular bone where it attaches to the base or semi-lunar surface of the coffin bone. Remember that the bone is rigid. It is attached to the laminae and a very flexible, highly sensitive blood barrier, which are both attached to the semi-rigid hoof capsule.

As down load is placed upon the limb, each structure comes into play. If we see the tendon as if it were a large “rubber band” attached to a highly sensitive coil (the muscle) programmed for delicate suspension, we can imagine the weight of the horse passing through the fetlock and lower digits causing them to reach maximum flexion.

If the suspensory is cut while the limb is in full flexion, the fetlock will remain very close to the ground. The suspensory is the major support for the fetlock joint. However, if the superficial tendon is cut, the fetlock will come up but not reach its original height. If the DDF is cut, the fetlock angle returns to its original relationship with the pastern.

Notice that cutting the DDF doesn’t affect the fetlock angle. Instead, it causes major changes within the hoof capsule. Apparently the suspensory is the major support for the fetlock while the DDF is the major support for the third digit. Radiographically, the coffin joint can be luxated as much as one-fourth inch depending on the unique characteristics of the digital alignment and the relationship of the hoof capsule to the ground.

After cutting the “rubber band,” the DDF tendon releases the down load that was once cradled in the sling. Therefore, the sling no longer exists. There is no longer direct pressure over the proximal sesamoids, the navicular bone, bursa and sole corium. PIII also floats forward because there is no structure left to hold it tightly against the articulation of PIII.

The impar ligament is a very strong attachment capable of supporting serious down load. When the DDF is cut, it also moves forward with the bone. The apex of PIII also tips upward as load is passed through the proximal digits to the articular surface of PIII. In absence of the support sling, the apex of PIII is pushed upward and forward. PII also moves in a posterior direction, transferring load to the caudal articular surface, navicular bone and impar ligament.

So, what has happened to the original pressure points?

The distal sesamoid acts as a pulley over a high-stress area to reduce friction and absorb energy. It also supports the coffin joint along the palmar surface. This hot spot is a high friction point, but the cutting of the “rubber band” has significantly diminished the amount if friction. Subsequently, the pain associated with this spot is immediately relieved. In addition, pathological lesions involving the tendon, bursa, bone or supporting ligaments are no longer tightly compressed against the opposing forces of the DDF tendon.

The palmar surface of PIII is concave with a very sharp solar margin along the anterior two-thirds of the bone. A student of mine once commented that, “it would make a terrific hatchet”. There is no doubt that this very thin, fragile border of PIII plays a role in its function. The question is, “How?”

When the sling is cut the bone tips upward, the action immediately releases down load against the very sensitive sole corium. Performing venograms on numerous sound feet with acceptable mass and “balance”, I found that lateral views revealed that the vascular complex of the sole measures one full centimeter in depth. The circumflex vessel is palmar to the surface of the bone and slightly outside the cutting edge of the bone. In some cases, the thin-soled horse may have only one centimeter of total distance between the bone and shoe.

The venogram reveals that the circumflex vessel is sandwiched between the wall and the bone. This serves a nice hiding place otherwise the cutting surface of PIII could cause irreversible damage. Suddenly relieving the down load against the delicate vascular supply not only relieves pain (the hot spot is no longer there), but it allows the vessels to perfuse (fill with blood) as never before. Observing the effects of literally hundreds of cases that were realigned immediately prior to a tenotomy, it is evident that perfusion results in sole proliferation.

Relieving this hot spot in acute laminitic cases is a major contributing factor for successful treatment. The bone acts as an anchor for the sensitive laminae, which basically remain functional as long as the basement membrane remains intact. When the function of the basement membrane is compromised, the desmosomes lose their adhesive strength and are pulled apart by the relentless pull of the DDF tendon. When the tendon is cut, this pulling force no longer exists and the desmosomes continue to remain intact.

Anatomically, the sensitive laminae are attached to the non-sensitive laminae, which are the inner zone of the hoof wall. Migrating abscesses can form puncture wounds, keratomas, white line disease, cause pathological lesions of the zone and subsequently cause pain due to the close association with the sensitive laminae.

This semi-rigid zone extends along the entire circumference of the hoof capsule. At the inner sole margin the laminae become modified and form the sole wall junction. These terminal laminae can be seen on the ground surface of a freshly trimmed foot and are erroneously called the white line. To be accurate, it is actually more yellow/yellow-brown than white.

Adjacent to this zone is the stratum medium, which comprises the bulk of the hoof wall. Its growth comes primarily from the secondary laminae. It is non-pigmented and appears white in color. Often it is erroneously referred to as the anatomical white line that was previously mentioned. It is the only white line on the exterior of the foot. This zone is continuous to the top of the coronary groove and is the primary site for white line disease.

When treating white line disease, one key ingredient is relieving the downward pull of the tendon against the bone, and the bone on the hoof wall. This action significantly reduces the tearing forces placed on the wall.

When looking at white line disease radiographically, a large lucent (dark) area can be seen just in front of the bone. It has an entirely different shape and location than the dark zone found with laminitis. However, the forces at play in both white line disease and laminitis are the same. The DDF is just pulling the wall apart instead of destroying the laminae. In both syndromes, extensive rotation and acute lameness can be evident.

The outer horn wall is made up of vertical tubules placed in close proximity. These tubules give stiffness, yet flexibility, to the wall. The growth of horn wall originates at the coronary groove. When this horn wall makes contact with the ground surface, it forms bars as it wraps around the bulb of the heels.

The result of cutting the DDF tendon immediately reduces the inner pull of the bone/laminae network, which significantly reduces the bending or dishing of the hoof capsule. The ground surface of this zone is the farrier’s workstation. Whether trimming or shoeing the foot, how the outer hoof wall contacts the ground or shoe surface is of the utmost concern. It is this zone that sets the stage for the counter action of the DDF tendon.

This is a short, basic summary explaining how the four-point system enhances natural healing by simply eliminating hot spots and subsequently enhancing perfusion. The four-point concept is a conservative technique with very similar mechanical advantages found with a tenotomy. Moving the pivot point back from the toe attenuates the tendon pull by simply reducing the counter pull. This is referred to as ease of breakover; the further back it goes the less pressure placed on the hot spots.

I refer to increasing the mechanics of the trim or shoe as reducing counter pull that opposes the tendon. Requesting a farrier to rocker the toe is meaningless unless a point of reference is used because all rockered toes have mechanical advantage. On a scale of 1-10, with 10 being equal to a tenotomy with normal digital realignment, most rockered toes fall into a 2-3 category. This is not bad. However, if you need quick results, quick growth, quick pain control, and optimum healing you need higher-scale mechanics.

In the late 80’s and early 90’s, I used a rocker toe technique on horses with chronic toe cracks, dished feet and thin soles. I also used this rocker toe trim to unload diseased, frayed yellow lines that had multiple black splits and associated horn cracks. The breakover or pivot point was placed on the foot perpendicular to the long axis of the frog, approximately 1/2 to 3/4 inch forward of the frog. The heels were pushed back to the widest point of the frog when possible. Simply unloading the areas that seemed to always pack dirt drastically reduced the number of gravels seen during wet weather, and it stimulated tremendous sole proliferation.

The four-point shoe soon followed as many mares were thin-soled, making it very difficult to move the breakover back to within 3/4 inch of the frog. My trim and shoe have slowly evolved over the years, and I am almost at the same rung on the ladder as my colleagues were 400 years ago. There has been some progress made because my four-point method now allows me the opportunity to help a multitude of problems with very consistent results.

My first four-point shoe had a square toe that put breakover approximately 3/4 inch forward of the frog, very close to the apex of PIII. I had great luck treating many thin soles and shelly walls, some with a heavy dish and full thickness toe cracks. I wasn’t satisfied with this shoe as it left a lot of toe hanging over the end of shoe. A horse that would paw a lot could easily bruise the exposed sole wall junction.

I shod many of the world’s best Thoroughbred stallions and mares with this design and helped them all, however the shoe had its drawbacks. Once I have identified negative aspects of a shoe, pad, nail or clip or a combination of all the above, I delete it from all future shoeing protocols. The square toe was deleted and replaced by a shoe with full toe cover and breakover at the widest point of the shoe. This gave me both protection and high-end mechanics.

Personally, I have no problem with any or all of the four-point concepts that float around the globe today. All four-point shoes have mechanical advantages that attenuate the tension of the DDF, relieving compromised growth centers. Still, there are questions that persist.

“How quickly do you want things to happen when shoeing a lame horse?” “What do you expect to see in four to six weeks?”

The answers to these questions depend on where you place the breakover. Ask ten farriers and you will get ten difference answers. Personally, I want a lot of foot growth in four to six weeks to protect sensitive areas. I feel my technique is an overkill compared to others, but I find great success with rapid sole proliferation. Plus, new sole triggers new wall growth.

Where shoes rank on the mechanical scale is dependent on where the pivot (breakover) is place relative to the apex of PIII. There is not a hard rule of thumb that describes the ideal breakover for all feet. Internal as well as external hoof characteristics influence the PSI needed to lift the heel from the stance position. Many other factors influence the lifting of the heel as the horse is propelled forward.

One would like to think that breakover 3/4 of an inch in front of the frog would have the same effect on all feet. However, experience has taught me better. The long toe-underrun heel foot with a –5 to –10 degree palmar angle and a 2.5 - 3 inch digital breakover often requires the pivot point to be well behind the coronary band. The opposite foot that is most often a grade 2 to grade 3 club with a +8 to +10 degree palmar angle has the center of load closer to the apex of the frog. This observation has taught me to adjust the pivot further and further under the foot when optimum mechanics are required. This aggressive breakover technique has offered my patients a quicker recovery time and allowed them to return to training much quicker than with my previous point of breakover. Contrary to the published materials that caution against placing the breakover behind the apex of PIII, I find it very useful and a means to relieve compromised growth centers.

Case 1

The case presented as a Grade 3 club foot with a dished hoof wall and growth rings twice as wide in the heel than in the toe. There was also slight remodeling of the apex. This foot was more narrow relative to the opposite foot, it had a prominent coronary band, 6mm sole depth, and was shod 3-4 weeks prior with a four-point rocker rail and 10-15mm breakover.

Response

There was 12-15mm of sole growth by the first reset (four weeks) and a slight reduction in the growth ring pattern. The second shoeing revealed 15-20mm of sole with slightly more toe growth than heel growth. The dish was almost grown out with the foot having never been backed up from the front. The third shoeing revealed a foot absent of a dish, 15mm sole depth with 5-8mm cup, and even toe/heel growth patterns.

Placing the breakover well behind the apex of PIII with an aluminum rail or air wedge rocker offeres me a consistent means of treating club footed yearlings with thin-soles and poor quality walls.

Using the venogram to demonstrate the simple physics on healthy feet, as well as diseased feet, we can identify areas of perfusion, the degree of filling and the areas with limited perfusion. Simply moving the breakover to the apex of PIII significantly increases perfusion of the sole corium and anterior lamellar vessels. The Redden Modified Ultimate with the breakover directly beneath the apex of PIII has a very similar pattern when films are made during the final stage of infusion while the limb is fully loaded.

Perform a venogram on a sound, healthy foot:

• Hoof angle measures 54-56 degrees

• HL zone measures15/15mm

• Sole depth measures 20mm

• Digital Breakover measures 35 mm

Be sure to load the foot during infusion of the contrast agent by picking up the opposite limb. Take all necessary film within 30 seconds. Your results will show stark loss of contrast along the lamellar vessels and sole corium distal to the apex.

Apply a four-point trim to the same foot pushing the heels back slightly and placing breakover at the apex of PIII and repeat the experiment. The laminae and sole corium routinely perfuse within normal limits. A similar pattern can be seen using the Modified Ultimates. Therefore, consistent data points to the action of the DDF tendon as the great mediator and clearly explains how we can consistently raise the heel on laminitic cases and use the four-point method on a multitude of pathological conditions with consistent success.

The four-point concept carries a strong message, and the results are dependent on the start model, the power of observation and skill of the farrier. Farriers without radiographic vision have a tremendous disadvantage. Knowing how to read informative film gives us all the opportunity to become more proficient in our perception of what lies beneath the sole.

Failure to accurately assess the start model can have serious consequences for those trying to use the four-point technique without fully understanding it. Misjudge the sole depth by 10mm and you have a very sore horse with the best part of his foot lying on the ground. Raise the heels on a laminitic horse with 5-10 degrees rotation, positive or negative, and you bite the dust without realigning the load centers.

I hypothesize that the four-point technique enhances the so-called “pump” of the foot. It is also my hypothesis that it is the action of the DDF tendon that significantly reduces blood flow to the anterior laminae when it is loaded and allows it to fill rapidly when unloaded.

Could this be the mystery pump? I think so. Moving large volumes of blood throughout the laminae with each footstep would be a logical explanation for the natural cooling system that prevents over heating when the foot is subjected to speed. It may also help argue the frog pump theory that most of us never bought anyway. The ungual cartilage must also play a role as an energy sink, (ref: Bowker). Hopefully future research will give us many of the answers.

My message to everyone is to relax and let the foot speak to you. Observe the effects of your efforts, whether they are positive or negative. Delete the known negatives and enhance the positives, use informative radiographs at all times, and the mechanics will come to you.