Updated: Apr 20
2003 - 16th Annual Bluegrass Laminitis Symposium Notes
How To Use Self Adjusting Palmar Angles To Treat Heel Pain
Written and presented January 2003 by R.F. (Ric) Redden, DVM
Traditionally we have been taught to speak of rotation as the most meaningful single pathological indicator within the hoof capsule. Owning and operating an exclusive equine podiatry practice for twenty plus years I must say I never have felt this particular radiographic perimeter to have any significant meaning. It often overshadows more important perimeters that offer endless information concerning drastic changes within the foot. Let's look at a diagram of a radiograph with the most important perimeters. The horn - lamellar zone would be the thickness of the horn, plus the laminae measured in two distinct locations. Any discrepancy in these figures would include a negative or positive capsular rotation or possibly over sculpturing of the horn wall. Neither of which will cause the horse to show the clinical pain that is exhibited with acute laminitis.
Palmar angle: Draw a line along the palmar (plantar) surface of PIII, I like to use a line along the wings as they are the natural load zone, and measure the angle they make with the ground surface. This angle becomes very meaningful when dealing with most all foot problems. Using this angle we can be very precise as we manipulate the foot in an effort to enhance the healing environment.
Sole Depth: Drop a line off the apex to the shoe surface or opaque wire that is in the top of the x-ray positioning block. If cup is present measure it as well and record, e.g. 15/3 = 18 mm. depth, 3 mm. cup = 15 mm. pure sole.
C.E. (Coronary band - extensor process): Draw a horizontal line through the coronary crest, another through the top of the extensor process. The distance between these two lines is the C.E., a very significant perimeter to monitor with laminitis.
How do we use the palmar angle to influence the mechanics? First let's consider the support sling of the digit. The deep flexor cradles the navicular bone pushing it against the articular surface of PII and PIII, attached by a very secure anchor to the semi lunar crest of the coffin bone which in turn is anchored to the wall with a very vascular - sensitive lamellar network. The pressure exerted on all these structures is influenced by body weight, speed, footing, conformation and the unique way in which the foot lands, torques and loads. The details of how the foot maintains a healthy state of equilibrium is based on the fact that all members or structures of the support mechanism perform as a healthy, fully functional unit. When one member fails the next one is challenged and soon a cascading series of events is well on its way. One should look at the palmar angle as if it were an idle pulley, working in the middle of a belt drive. Adjusting the tension on the pulley increases the load on the belt as well as the end points. The palmar angle does much the same, but it is located inside the belt so to speak and when the palmar angle is lowered pressure is applied to the tendon, bursa, apex, sole corium, laminae and horn wall. The slightest adjustment greatly effects the circulation as well as sensitivity of the digit. Coupled with the effect of the support outside the sling is the digital cushion, frog, sole, buttress and horn wall. All of which function as energy sink while protecting the sensitive structures.
Let's take a look at the hot spots or excessive load zones with a typical pathological case. Navicular disease we will simply call heel pain as it is a multi facet syndrome as a rule with several sensitive structures involved. Using a lateral radiograph, (farrier friendly view of soft tissue detail, pure lateral radiographs with wall and ground markers), let's look at the effects of chronic hot spots. Most cases will exhibit excessive pain to hoof testers with placement over the center of the frog. Many also show pain across the heels, and will resist thumb pressure when pressed deep into the heel bulb area. Most will block with a heel block and often an intra-articular when given a few more minutes to soak in. Most do not like to walk or trot down hill. Most hate it with a passion and do not like to turn in a tight circle especially on hard footing. Discounting the fact that we are looking for a diagnosis, let's consider looking for hot spots and a mechanical solution that simply takes the pressure or load away from the heel area significantly improving the healing environment. I do not need a diagnosis to feel good about fixing a lame horse. I need a solution and so does my client.
Let's review a typical radiograph; toe angle 50 - 52 degrees, sole depth 15 mm. (no cup), zero palmar angle, horn - lamellar zone 15/15 mm., C.E. (coronary band - extensor process) 15 mm. with proximal wall bending (high dish just under the coronary band). Radiographs reveal slight lipping at the apex, mild to moderate pedalostitis along the wings of the coffin bone, several small lucent areas superimposed over the body of the navicular bone (seen in several grid views). Many very similar cases will have distinct osteophytes within the impar ligament, spurs on the wings of the navicular or possibly no radiographic lesions but with an identical history. How significant are the radiographic lesions? It is debatable depending on the precise location and effect on surrounding sensitive tissues. Regardless, it really doesn't matter as we have a very consistent means of reducing the pressure to this area. Traditional methods of treating heel pain has been eggbars with slight heel elevation and a pad of some sort, all of which have merit but very low on the mechanical scale. The eggbar supports the tendon apparatus not the heel. It actually increase load on the heel which supports the tendon, but this slight benefit reduces load over the bursa and bone. The wedge can act to decrease pressure over the bursa area also, depending on the relationship of toe angle, navicular bone angle, sole depth and palmar angle. Raising the heel can have a negative effect when only a few degrees are put on a foot with negative palmar angle. Eggbars are so popular because they are inexpensive, easy to apply, and often offer immediate relief of pain to some degree, a horseman's dream. Unfortunately they seldom if every improve the quality, mass of foot, and most often slowly crush the heel tubules reducing mass of cushion and wall strength. Sole depth remains constant (normally thin) therefore the mechanics are not sufficient to offer a better healing environment. Most eggbars are a temporary Band-Aid® that offers temporary relief.
The palmar surface of the navicular bone can act as an idle pulley also. It is greatly influenced by pastern alignment. The proximal border of the bone is firmly attached to the back of PII. Broken back axis can increase the palmar angle of the navicular bone while the palmar angle of PIII becomes lower. This is not a good deal as many sensitive structures become part of this syndrome. Very simple mechanics designed to significantly raise the palmar angle of PIII shifts load away from the apex, navicular bone and lamellar zone toward the heel and can have a profound effect on the hot spots. Considering the start point of the existing palmar angle, the goal is to raise it several degrees above the normal palmar zone of a healthy foot with similar conformation. The palmar angle on a large majority of normal feet will fall in the range of 3 -5 degrees on front feet and 5 - 8 degrees on hind feet. Unfortunately a large number of performance athletes have various degrees of heel compression which can be seen as a diminishing palmar angle. This can be confusing to many as it is normally seen, but what is actually normal and healthy can be quite another finding. Grade 2 clubs and higher will naturally have larger palmar angles unless they have been trimmed and shod in a fashion that diminishes heel mass.
I have found that wedges push the palmar angle into the desired sweet spot but increase the load on the heel tubules and soon they begin to breakdown. Using breakover or pivot well under the foot offers self adjusting palmar angles. The horse pulls the heel up with the easy toe action by shifting load quickly to the toe. The mechanical efficiency of the shoe can be scored by giving the shoe a point for every two degrees it raises the palmar angle. This is static load evaluation (standing equally on two x-ray blocks) reviewed radiographically. Being able to see this magic relationship at speed and all stages of the load phase would be nice. Let's take an example. Start angles negative five degrees (apex tipped up) put on a rock-n-roll shoe that brings the starting palmar angle up to positive 10 degrees. This would be a 7.5 point shoe. With an acute laminitis case, I like to have a 20 degree palmar angle, therefore we need 25 degree raise or a 12.5 shoe for the foot that is negative five degrees. Traditional shoes with a rocker toe or rolled toe have very limited mechanics as the breakover is limited to the toe branch of the shoe and when this is placed behind the apex the level of mechanics goes up and they move as a unit. We found drastic radiographic differences month after month. The palmar angle, sole depth, and digital alignment relationship become part of the formula as well. Regardless, any and all shoes designed to reduce breakover have positive mechanical properties. How much depends on the previous location of the pivot point and the unique characteristics of the start model. If we look at a foot (regardless of the start model characteristics) shod with a heavy square toe versus the same foot shod with a rock-n-roll shoe, moderate belly, placed directly below the center of articulation of the coffin joint. Photographs and radiographs clearly reveal the stark difference in the effect on the palmar angles. The square toed shoe doesn't change the palmar angle unless the horse moves forward, this is the only time he feels the effects of the mechanics. Not bad, certainly helps performance but is slow to improve sole depth, heel mass and realign tubules. Why? It only works when the horse is moving, if movement is the greater part of his day - great, things will happen. If not, the radiographic perimeters do not change. The rock-n-roll shoe immediately changes the palmar angle at the will of the horse, placed as described the horse has a choice of load zones and they are not going to purposely increase tension on hot spots. If he sleeps standing all day and doesn't move a foot the horse is constantly providing a better healing environment which is easily demonstrated by accelerated sole growth, improved tubule alignment, buttress remodeling, horn growth and overall foot mass.
The clinical effects of altering the palmar angle can be very rewarding with many of the common syndromes that are merely hot spots or over stressed areas that have become dysfunctional due to disease or injury. The genetics of the beast has a very intricate healing protocol that we understand a little better all the time. Give Mother Nature a chance to do her thing simply by removing the handicaps and things start to happen. I like to think of healing with the hope of a cure. Many horses can heal sufficiently enough to not feel pain but are never cured of the original problem.