03/04/2026
What actually is the argument about Hoof Pastern axis?
I think one of the biggest sources of confusion in hoof balance discussions is that people think we are arguing about angles and lines, when in reality we are arguing about mechanics.
Very often the hoof pastern axis discussion gets reduced to “straight is good” versus “there is bio-diversity so straight doesn’t matter.” But that is an oversimplification of what is actually a much more interesting and much more three dimensional problem.
Even if we set the literature aside for a moment and just look at this from first principles, mechanics, physics, and what we repeatedly see in practice, hoof balance is not a purely two dimensional geometric problem. It is a three dimensional spatial equilibrium problem.
At mid-stance, when the limb is loaded, the system is trying to resolve forces around the centre of rotation of the distal limb. For equilibrium to occur, you effectively have to align two vectors and one point in space. The ground reaction force vector, the internal force vector, and the point about which those forces are acting must become spatially coordinated. When they do, net moment is minimised and the system becomes mechanically efficient. Static HPA is therefore not the goal in itself, but it is a proxy for what is happening at mid-stance.
This is why I often say that HPA reflects the relationship between the centre of pressure and the centre of rotation, and its relationship with the solar support base. When those relationships are spatially coordinated, the external geometry often falls into a certain range.
This is also where the banana shoe becomes so interesting, not just as a therapeutic tool, but as a mechanical demonstration.
If the shoe creates a non equilibrium state and then allows the foot to move, the system responds by rotating until it reaches the lowest cost shared load state available under those conditions. That is the important point. The shoe does not force the foot into a chosen angle. It removes resistance and allows the limb to express what the mechanics demand.
What happens then is extremely revealing.
When the system is given the freedom to move toward equilibrium, it settles into a position where the moments around the centre of rotation are reduced and the load is shared more efficiently. In practice, that settled state very often corresponds to near phalangeal alignment and a near straight hoof pastern axis.
That does not prove that every horse must be forced into a perfectly straight line. But it does expose something very important. When the digit is allowed to express the lowest cost equilibrium state, it does not usually settle into grossly broken alignment. It tends toward near alignment.
That is not dogma. That is signal.
The banana shoe therefore gives us a clue about the mechanical truth of the system. It suggests that near alignment is not just an aesthetic preference or a traditional ideal. It may be the external expression of a state in which the digit can share load with the lowest internal mechanical cost.
That is why I think this example matters so much. It shifts the conversation away from “what angle do we like” and toward “what state does the system itself choose when it is allowed to resolve force efficiently.”
I fully accept that there is bio-diversity between horses. Biology does not work in absolutes and we should not be forcing every horse into a rigid dogmatic straight line. But bio-diversity does not mean randomness either. Most biological systems exist within a normalised distribution, a bell curve, with a working tolerance around an optimal zone.
In my own documentation and experience, and as illustrated in the attached image, when you look across breeds and types of horses, and you remove the cases with obvious morphological distortions that significantly alter heel to toe height ratios, a large proportion of equine digits tend toward a near straight hoof pastern axis. Notice the wording carefully. Near straight, not perfectly straight.
That suggests that when the system is free from gross distortions and allowed to function within reasonable mechanical parameters, the external alignment often normalises toward a certain range regardless of breed. That does not eliminate bio-diversity, but it does suggest that bio-diversity lives within a range, not across infinite possibilities.
It is also important to acknowledge that HPA is not determined by the foot alone. Posture plays a huge role. Whole horse posture, limb orientation, muscle tone, and the way the horse organises its body over the limb all influence the orientation of the pastern and therefore the external HPA we observe. So we must be careful not to treat HPA as a foot only measurement. It is a whole limb and whole horse expression, not just a trimming parameter.
Another point that is often misunderstood is that a near straight external hoof pastern axis does not necessarily mean perfectly straight internal phalangeal alignment. External geometry is a proxy, not a direct measurement of internal joint angles. You can have a near straight external HPA with small variations in internal joint angles, and you can also have a straight looking dorsal wall that hides internal misalignment. This is why we must always remember that external landmarks are approximations of internal mechanics, not perfect representations of them.
So the goal should not be to force a textbook straight line. Nor should the goal be to abandon any idea of an ideal because of bio-diversity. The more rational position is this.
We should aim to create a situation where the mechanics of the limb can be satisfied, where forces can be resolved efficiently, and where the tissues can function within a reasonable mechanical environment. If we achieve that, then the external geometry, including hoof pastern axis, will usually fall within an appropriate working range for that individual horse.
In that sense, having an ideal is useful, not as a rigid rule, but as a direction of travel. An aim with tolerance is very different from dogma. But having no aim at all, and attributing everything to bio-diversity, risks us losing any mechanical reference point altogether.
What we really need going forward is more work to establish working tolerances. We need to better understand where normal variation sits, and at what point changes in internal joint angles or external alignment move from normal standard deviations into pathological patterns.
That is where I believe the discussion should be heading next. Not arguing about whether straight lines are good or bad, but trying to define the functional ranges within which the limb can operate efficiently, and beyond which mechanical compensation and pathology become more likely.
Because in the end, the question is not “does it look straight?”
The question is this.
When the system is given the freedom to express the lowest cost shared load state, where does it settle, and what does that tell us about normal function? And where are is the range of tolerance?