This is the plane most commonly observed when addressing hoof balance. Common terminology includes hoof pastern axis, hoof angles, rotation of the coffin bone, long toes low heels, club feet, break over, heel support, all of which reference this plane. I believe all discussion of balance in this plane is speculative without the accurate measurement of two parameters: P3 bottom angle (palmar angle of the coffin bone) and the toe/support percentage. These two numbers are obtained from computer analysis of a high standard lateral radiograph and give a good indication of how far in or out of balance a hoof truly is within this plane. Moreover, these parameters can be adjusted with profound effects upon the biomechanics of the digit.

The P3 bottom angle is the true measure of whether or not an individual hoof is upright or under run. There is some debate as to the normal range of this parameter but the current consensus is that it should be between 2.5 and 6.5 degrees. P3 bottom angles at or below zero and above 10 degrees will most certainly be associated with some degree of pathology.  The P3 bottom angle is the measure of how the hoof capsule presents the coffin bone to the ground plane. This position is under the influence of the hoof capsule as a whole, the deep flexor tendon, the dorsal laminae and the distal interphalangeal joint.

P3 bottom angles that are out of the physiologic norm create a multitude of dysfunctions. We will begin with the upright hoof which is surprisingly more common than the truly under run hoof (see graph on lateral image page).  These can be a poorly trimmed hoof, a club foot, or a laminitic hoof. Laminitis will be dealt with as a subject all its own. These hooves are characterized by P3 bottom angles of greater than 10 degrees.  An interesting phenomena is noted on radiographs of horses forced to exist in this state for prolonged periods. The coffin bone will remodel at is distal tip to what would be a more normal angle (see photo on lteral image page).  When the coffin bone is to upright to the ground, the load is transferred inappropriately forward on the hoof. This broken forward conformation transfers load onto the sole at the pedal margin instead of through the frog and unguanal cushion. Unable to perform this energy damping function the whole digit suffers excessive stress. These hooves are predisposed to thin soles, bruising, pedal osteitis, laminitis, ring bone, thrush, contracted heels, frog atrophy, thin weak hoof walls, and dishing toe to name a few. There is often reduced toe growth and accelerated heel growth which further compounds the problem.

Treatments applied to these types of hooves are aimed at promotion of a normal P3 bottom angle by lowering the heels and correction of any associated sequela. Perhaps the single most important therapy for these hooves is early identification and surgical intervention via an inferior check ligament desmotomy. This procedure can permanently normalize the P3 bottom angle by releasing tension on the deep flexor tendon. Excellent long term results are achieved in individuals less than six months of age. Positive results decline with maturity.

A variety of what are known as adjustable palmar angle shoes (rock-n-roll shoes) can be applicable in these situations. However, the reality of the upright or club foot is that the excess heel often needs to be removed as frequently as every 2-4 weeks if they are to be kept any where near balance. For this reason, many of these horses can be better managed without shoes, provided the hoof capsule is in fair to good condition with ample sole thickness.  These hooves are typically not in good condition and the decission to go unshod should not be abrupt and may not allways be possible.

Excessive palmar angles are also seen when an individual is incorrectly “stood up” by allowing excess heel growth or through the inappropriate use of wedge pads. The correct way to stand a horse up is by lowering the heels while simultaneously reducing the toe percentage, more on this later. Many horses that appear to have an under run hoof capsule have a normal P3 bottom angle and do not necessarily benefit from heel wedging.

The vast majority of horses that appear to be under run in the heel, often have excess amounts of toe, or toe/support percentages above 65% with a relatively normal P3 bottom angle. Which brings us to the second critical parameter in the lateral medial plane. The toe/support percentage is the amount of hoof that is in front of the center of articulation of the coffin joint.  A detailed paper on how this center of articulation is calculated can be found at www.eponatech.com. Individuals with a toe/support percentage much in excess of 60% are on the verge of over stressing the hoof, the coffin and pastern joints, and the structures of the navicular apparatus. This parameter and its center of articulation is also a key component in our calculation of an ideal break over point for a given hoof. Details on break over can be found on the “get ’er done” page. The reality of the matter is that long toes cripple horses and this parameter is the measure of just how much toe a horse really has. 

Analysis of the toe/support percentages and P3 bottom angles on upwards of 1000 radiographs have led me to one profound conclusion. Things are not always as they appear even to the trained eye. Hooves that look normal can have excessive amounts of toe and vice versa. Hooves that appear under run may not be and hooves that seem upright may not be. Taking the radiograph and doing the analysis is the way to get the facts on how to achieve balance in this plane.