© Anne Daimler, FL

Fig. 5                          Fig. 6                        Fig. 7

Underrun heels area often considered to be “low” or as “having no heel”. Here the heel is underrun but so long that it is causing an incorrect, broken-forward hoof pastern axis (Fig. 6).  After trimming, the heel, while still somewhat forward, is shorter and the hoof pastern axis is much improved (Fig. 7).

Original photo courtesy of Julie Leitl, Victoria, Australia

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Underrun heels are defined by comparing the heel tubule angles to the toe wall tubule angles. They should be parallel. If the tubules converge (in the lateral view) from their starting point at the coronet towards the toe, they are underrun. Harder hoof wall is less prone to being crushed into this geometry so the horse with genetically harder feet is better off to start with (in this respect).

There are specific trimming techniques for preventing heels from becoming underrun, if the horse is left barefoot. In general, the heels would be trimmed frequently (in this case, perhaps once a week), bringing them back to line up with the widest part of the frog. Then, one would also relieve, or float, the quarters very slightly under the heel area to prevent the tubules from being crushed by the weight of the leg and start running forward.

It’s also essential to keep the toes as short as possible to avoid drawing the heels forward as the toes grow forward. Maximum turnout is also helpful to prevent ammonia from weakening the tubules and allowing them to become crushed.

Fig. 1                                               Fig. 2

Photos above illustrate an underrun heel.  The superimposed lines in Fig 2 follow the direction of the tubules. In a healthy hoof the tubules are diverging or at least parallel – here they would converge if the lines were extended beyond the toe.  The angle the heel tubule makes with the ground is more acute than the one the toe tubule makes with the ground, which is incorrect (Fig. 2)

    © Julie Leitl, Victoria, Australia

Fig. 3                            Fig. 4

Another example of underrun heels, with the weightbearing point having grown far forward onto the sole (Fig. 4, yellow arrow). The pink arrow shows where the heel should be, i.e. even with the widest point of the frog.

This foot also looks like it may have a negative plane coffin bone, which seems to occur more frequently on hind feet. 

Navicular ‘changes’, as seen on radiographs, are nearly meaningless in diagnosing ‘caudal heel pain syndrome’; in fact I wonder why they bother taking them. If the horse is lame you don’t need an xray to tell you so, nor do any of the treatments address the lesions or cysts that are considered to be the cause of the problem.

Orthopedic or corrective shoeing works in the short term by restricting the blood supply to the navicular bone by increasing the angle of the hoof/pastern axis, which compresses the artery that enters the foot in that region.  It is counterproductive to prescribe shoeing that continues the conditions that caused the problem to begin with.  In particular doing so on a young horse will predispose it to this condition for the rest of its life and will shorten its productive lifespan.

Shoes on a horse who has not fully developed his skeleton can be very detrimental in that they restrict the coffin bone from reaching its full developmental characteristics. It restricts the amount of space available for the structures located in the flexible rear part of the hoof and prevents proper development of the palmar processes which by means of the lateral cartilages attach the coffin bone to the short pastern bone.  

A more productive course of action would be to address the problem by means of a physiologically correct trim, removing excess, hard horn that is causing pain and inflammation and leading to ‘caudal heel syndrome’.