COLLAPSED HEELS/NEGATIVE PALMAR ANGLE.
Has your horse been described as having any of the following: collapsed heels, under run heels, under slung heels, long toe/low heels, ground parallel coffin bones, negative palmar angle?
The palmar angle is the angle that the base of the pedal bone has to the ground.
Below: a positive palmar angle in a sound barefoot horse.
Below: a ground parallel coffin bone.
Below: a negative palmar angle.
Some schools of thought believe that the coffin bone should be ground parallel, but I agree with Pete Ramey who suggests that during stance the coffin bone should have a positive 3-8 degree angle. At peak loading (galloping/jumping) the heels expand allowing the back of the pedal bone to drop, so that it becomes ground parallel to give maximum support. If the coffin bone is ground parallel during stance then it will be in a negative angle at peak loading.
Ground parallel or negative coffin bones will be seen externally as a foot with long toes/low heels or collapsed heels. The example below also shows the same foot after 2 months of natural hoof care, just to illustrate that this isn’t the horses’ natural hoof conformation and is easy to correct. This is a severe example of collapsed heels on the hind feet of a 5 year old horse. The red lines follow the angle that the hoof is growing in. The tubules are bending under the pressure. The yellow line highlights the farrier’s efforts to control the problem by rasping the toe back as far as possible, but the unnatural affects of the shoe make improvement difficult.
WHY IS THIS A PROBLEM FOR THE HORSE?
Ground parallel coffin bones and negative palmar angles affect the angles of the leg joints, altering the way the horse stands and moves.
If the hind feet are affected the horse is forced to stand with the feet too far forward under its body, so that the cannon bones are not perpendicular to the ground (above). The hocks are under pressure pre-disposing the horse to bone spavin. The hamstrings are tight, and there is tension in the hind quarters and back. The discomfort causes resistance to the bit, reluctance to work in an outline, and sometimes more dangerous resistances like bucking. Owners report time and again that correcting this problem brings rapid improvement in the horses performance and temperament. These observations are supported by the following study:
Long Toes in the Hind Feet and Pain in the Gluteal Region: An Observational Study of 77 Horses.
Richard A. Mansmann, VMD, PhD, hon. Dipl. ACVIM, professor emeritus at North Carolina State University's College of Veterinary Medicine set out to determine if long hind toes could be a cause of gluteal (the muscles that run along the back of a horse's hindquarters on either side of the tail) pain in horses, and if corrective trimming and/or shoeing could correct the problem and eliminate the pain.
The researchers evaluated 67 shod horses and 10 barefoot horses with long toes. In the group of shod horses, 50 out of 67 tested positive for pain upon palpation of the gluteal muscles (i.e., displayed an exaggerated response to palpation that consisted of one or more of the following: buckling of the hind limbs, pinning the ears back, threatening to kick the examiner, or kicking at the examiner) and 17 horses tested negative (did not react to palpation). In the group of barefoot nonpregnant broodmares (all housed in the same environment and not being ridden) all 10 displayed positive reactions to palpation.
To evaluate whether corrective trimming or shoeing could resolve the gluteal pain, the team reduced the breakover distance (shortened the toes) in all the painful horses' hind feet and re-evaluated the animals:
Only 24 shod horses (of the 50 that had been found painful) were available for a follow-up evaluation four to six weeks after corrective trimming or shoeing; however, all of those horses showed reduced gluteal pain. Twenty of the horses were negative for a reaction to palpation and the remaining four were only mildly positive (the researchers noted that all four of those were negative to palpation after another four to six weeks and a second corrective trim). All of the barefoot broodmares received follow-up evaluations one week after corrective trimming. Eight of the 10 were negative for reaction to palpation and two were mildly positive.
"Excessive toe length in the hind feet might be accompanied by pain in the gluteal region," Mansmann wrote in the study. "Shortening the toe can alleviate this pain within days or weeks." The team added that "in cases where the toe length or gluteal pain was adversely affecting the horse's comfort or function, one could also expect an improvement in the horse's gait and performance after remedial trimming or shoeing."
Mansmann explained that most horses in need of a hind end evaluation will display behavioral problems including not performing as expected, not being willing to move off the leg, or stopping at jumps. He also noted that these horses might display signs of a sore back.
Click here to read more on this research - http://www.thehorse.com/ViewArticle.aspx?ID=18195
In the front feet palmar heel pain (pain in the back half of the foot) can contribute to the development of long toes low heels in the hind feet, because the hind feet are placed too far forward under the body to take weight off the front feet . The horse pictured above has his front feet positioned too far back, trying to put more weight on the front of the foot and less on the back of the foot. His hind feet are positioned too far forward, taking more weight off the front feet. Having the hind feet forward increases weight on the heels so that they collapse.
Negative palmar angle in the front feet is a factor in navicular syndrome. In this x-ray of an affected hoof a line following the pastern passes straight through the navicular bone. This forces the navicular bone into an unnatural and damaging weight bearing position.
WHAT CAUSES THIS PROBLEM TO DEVELOP?
There are several ways in which shoeing causes hoof deformation that leads to collapsed heels:
Shoeing results in lack of support for the heels. Sometimes shoes are purposely fitted that are too short at the heel. This is done with horses that pull their front shoes off with the toe of the hind foot. But even when shod with plenty of length at the heel of the shoe, as the hoof grows longer it grows forward taking the shoe with it and the support from the heel (right).
Below: A foot that is due for shoeing. Note the distance from the heel of the shoe to the vertical line dropped from the back of the heel bulbs. Compare this to the same hoof trimmed to an appropriate length. The heels have been brought back under the horse and are able to provide better support. This horse had been well shod, this lack of heel support is inevitable as the weeks pass.
Below left: This is the foot of a 20 year old horse. Long term lack of support has caused the heels to drop. Below right: After 7 months of natural hoof care.
Another problem with shoes is that nature designed everything on the base of the foot to bear weight. In fact with a healthy bare hoof on conformable surfaces (in the arena and on grass), most of the load is supported centrally, directly under the pedal bone. The hoof walls have a role to play in weight bearing, but are not the sole weight bearing structure. But when shod the base of the foot is lifted off the ground, and the weight is born via the hoof walls attachment to the pedal bone. Effectively the skeleton is suspended from the hoof walls. In the case of collapsed heels the hoof wall isn’t strong enough to support the weight, and the horn tubules bend (below left and 2 months out of shoes – below right).
Another factor is the need to rasp the base of the foot flat in preparation for a shoe. Horses naturally have a slight arch at the quarters of their feet. If this arch is ignored there is increased pressure at the quarters, which pushes the wall outwards. The outward bend of the wall at the quarters pulls the heels forward and under.
WHAT ABOUT SHOEING WITH HEEL WEDGES?
It might seem obvious to simply raise the heels with a heel wedge and shoe. But by continuing to shoe you won’t remove any of the causes listed above, and the wedge adds to the problem.
Here is a quote on the use of wedges from farrier Martin Deacon FWCF in his book “No Foot No Horse”:
“In the long term they create more problems because they act to crush the horn tubules at the heels even more. Therefore you create a vicious spiral – the heels are collapsed, heel wedges are applied, these crush the horn tubules at the heels, which leads to more collapse at the heels”.
Here is a quote from farriers Haydn Price and Rod Fisher from their book "Shoeing For Performance In The Sound And Lame Horse":
"It was and sometimes still is, a misconception that a long foot and broken back hoof/pastern axis with low, weak heels could be corrected by the application of wedges under the shoes at the heels. By raising the heels, so the argument runs, the whole leg would be raised and the height of the heel would be restored since the weight of the horse would be thrown on to the toe and reduced on the heel. In practice, the opposite effect is achieved. The back of the foot may be raised in the resting leg, but the full weight of the horse must still pass through the upright column of the leg during maximum weight bearing. By trying to insert a wedge under the heel, the pressure on the heel is actually increased. Compression of the heels leads to destruction of the wall and contraction of the heels."
SO HOW CAN WE CORRECT THIS PROBLEM?
Removing the shoes and applying a natural trim that corrects the long toe, will go a long way to correctling collapsed heels. However, by the time this course of action has been taken, there is an added complication that the digital cushion has fallen out of use. This is why heel wedges don’t work, because the support needs to be on the inside in the form of a thick digital cushion.
In the photo on the right I have highlighted the digital cushion in red. You can see how the thinner this wedge shaped structure is, the lower the palmar angle will be. The development of the digital cushion is a key factor in the angle of the coffin bone and therefore heel height.
Poorly developed digital cushions result from lack of stimulation to the back half of the foot. This is commonly due to lack of movement (too much time stabled), shoeing (raises the frog off the ground), and frog infections (makes the area too tendor to use normally)
Digital cushions only improve with use. But they won’t improve unless the frog is in contact with the ground (no shoes) and the foot is placed down heel first. Plenty of correct movement and exercise is essential. Taking the shoes off and turning the horse away will result in slow to non-existent progress.
Riding can generally be barefoot on soft going, but boots and pads are needed on hard and rough going to make the horse comfortable placing his feet heel first. Also treat any frog infections as tender frogs stop the horse moving heel first. Hind feet have better digital cushions because the way the joints of the hind leg move means that the horse has no choice but to put the hind feet down heel first, and so simply removing the shoes and applying a natural trim results in rapid improvement in hind feet.
Above: Walking uphill will cause any horse to place his feet down toe first hoof, and downhill - heel first. Get your eye in watching your horse being lead up and down a slope, then watch him walk on a level surface to see which his preference is. If he places his feet toe first he is avoiding impacting on a weak and tender back half of the foot.
The following photos show how with correct stimulation a weak digital cushion can improve, raising the heels and improving the palmar angle. These photos were taken 5 months apart (this event horse worked hard most days of the week).