I want to get back to this issue of the palmar / plantar angle (P-angle) and what the anatomically 'correct' range of angles is.
When a vet speaks about 'rotation', s/he is referring to the difference between the angle of the dorsal wall of the hoof capsule and the angle of the dorsal surface of the pedal bone (P3) - to a hypothetical ground plane.
When a vet speaks about 'rotation', s/he is referring to the difference between the angle of the dorsal wall of the hoof capsule and the angle of the dorsal surface of the pedal bone (P3) - to a hypothetical ground plane.
A front hoof may have a dorsal angle of 55 degrees with a pedal bone also at 55 degrees but that arrangement of the bones will not be considered to be 'rotated' even though the pedal bone is sitting at 10 degrees or so above ground parallel.
In this example, the bone is clearly at a different angle to the hoof wall and it is broken forward at the coffin joint.
The question is - does that steepened hoof form lead to lameness and to what the vets term, 'rotation'?
Strasser argues it does and she uses two different terms to delineate the situation where the boney column is misaligned (rotated out of its physiologically normal alignment to the ground and / or the other bones of the limb); and the situation where the bone and the capsule are no longer parallel to each other. She calls the bone misalignment 'rotation' and the difference in dorsal angles, 'separation'.
It is therefore possible to have rotation without separation; separation without rotation, or both.
Strasser argues it does and she uses two different terms to delineate the situation where the boney column is misaligned (rotated out of its physiologically normal alignment to the ground and / or the other bones of the limb); and the situation where the bone and the capsule are no longer parallel to each other. She calls the bone misalignment 'rotation' and the difference in dorsal angles, 'separation'.
It is therefore possible to have rotation without separation; separation without rotation, or both.
In a previous blog I said that a positive P-angle (forward of ground parallel) will be more easily tolerated than a negative P-angle. The effects of a persistent, slightly positive P-angle on the suspensory apparatus of the fetlock and that of the coffin joint, the laminar connection and the solar corium etc are less immediately obvious than the effects of even a slight negative angle.
All joints have an optimal 'neutral' position and for the horse this is especially important because it is only when the joints of the whole body are in neutral range that the stay apparatus, with its system of lever forces, balances and alignments, enables the horse to fully relax its skeletal muscle whilst upright.
The horse did NOT evolve to rest whilst recumbent - on the contrary, it gets most of its 'rest and recuperation' as an adult whilst it is upright. The younger horse may cope well with misalignments that compromise its stay apparatus, it may even survive into old age, but there will be damage. Depending on the indiviudal's genetic blueprint and its interaction with its environment, that damage may have an early onset and may be catastrophic, or it may manifest in symptoms and conditions that are not easily seen as having anything to do with a compromised stay apparatus.
Put simply, a horse than cannot engage its stay apparatus optimally is en route to a host of locomotor and metabolic problems.
The vexed question of course is what is optimal? We sit down and lie down to rest and to sleep and we may not easily understand from our own experience what it feels like to the horse not to be able to relax its skeletal muscle fully when upright. Try holding your arm out sideways at shoulder height for any length of time and that question is quickly answered. The horse's flexor and extensor muscles, like those in its back, are normal skeletal muscle, ie they are structured to act across joints to effect movement by contracting and relaxing/playing out, they are not meant to be persistently contracted. Persistent contraction leads to energy deficit and damage.
The vexed question of course is what is optimal? We sit down and lie down to rest and to sleep and we may not easily understand from our own experience what it feels like to the horse not to be able to relax its skeletal muscle fully when upright. Try holding your arm out sideways at shoulder height for any length of time and that question is quickly answered. The horse's flexor and extensor muscles, like those in its back, are normal skeletal muscle, ie they are structured to act across joints to effect movement by contracting and relaxing/playing out, they are not meant to be persistently contracted. Persistent contraction leads to energy deficit and damage.
You have only to look at the structure of the pedal bone to see how improbable it is - in evolutionary terms - for a bone of its shape and structure to sit at 10 degrees or so above ground parallel - especially in the main load bearing limbs. It is equally improbable that the hind hoof pedal bone, which is always steeper and more concave than the fore foot bone, should sit ground parallel and have a shallower dorsal angle than the fores. So common is this in conventionally managed horses, skeletons in museums have been assembled with the fore and hind pedal bones reversed.
Many farriers 'dress' the front hoof to have a positive P-angle, and the hinds to be ground parallel. I would welcome an explanation of the anatomical and physiological logic of that.
Many farriers 'dress' the front hoof to have a positive P-angle, and the hinds to be ground parallel. I would welcome an explanation of the anatomical and physiological logic of that.
An argument for the positive P-angle in the fore feet is that the horse lands heel first, and if the pedal bone is ground parallel when the hoof is unloaded, the heel first landing will stress the back of the coffin joint. And indeed that may the case when the soft horn/soft tissue structures of the rear part of the hoof and the suspensory apparatus of the coffin and fetlock joints are compromised.
Heel first landing occurs as the limb is being retracted and the hoof not so much lands, as touches down heel first at faster paces. Generally the horse lands flat in a slow walk. At a faster pace, both the number of times a given hoof touches down and the impact force increase, but the time each hoof is on the ground decreases. The faster the horse is moving, the more fleeting any given point is, in other words, the number of touch downs increases, the time any part of the hoof is on the ground decreases. Full load occurs as the body weight passes over the vertical axis of the limb when the whole hoof and the coffin joint is equally and evenly loaded.
In an optimal limb the back of the hoof is strong and deep, ie the lateral cartilages are thick and not deformed, the frog pad is deep and strong, the digital cushion is not degenerated into fatty tissue, the wall and bars are strong and retain vertical integrity; the suspensory apparatuses of the fetlock and coffin joints are strong and healthy, and the flexor muscles are strong and healthy and in balance with the extensor system.
If the limbs of the horse are in optimal condition from ground to spine and the stride is normal, why would the coffin joint with a GP pedal bone over extend under load?
The fetlock and coffin joints have sesamoids to increase their surface area - to spread load and to enable them to go through a greater range of motion. The fetlock joint has a far greater range of motion than the coffin joint obviously and has a complex system of back up with first the superficial digital flexor tendon and then the deep digital flexor tendon coming into play with their respective check ligaments that serve to protect the belly of their muscles.
Problems for the suspensory apparatus of the coffin joint arise when the stay apparatus is compromised by persistent misalignments, and / or the back of the hoof is weak.
A common example of a weak caudal region is a long but low heel (underslung); deformed, splayed bars; deformed and thin lateral cartilages; thin prolapsed frog; degenerated digital cushion; compressed bulbs. Such a hoof exposes the back of the coffin joint to stresses.
But the answer to this hoof form is not to stand the pedal bone on its tip by elevating the heels, but to trim and manage the horse so it can regrow a strong heel that can retain vertical integrity.
Yep - easier said than done -and success depends on a fairly intact bone. So, the best answer is, don't let the hoof get like that in the first place!!!
Heel first landing occurs as the limb is being retracted and the hoof not so much lands, as touches down heel first at faster paces. Generally the horse lands flat in a slow walk. At a faster pace, both the number of times a given hoof touches down and the impact force increase, but the time each hoof is on the ground decreases. The faster the horse is moving, the more fleeting any given point is, in other words, the number of touch downs increases, the time any part of the hoof is on the ground decreases. Full load occurs as the body weight passes over the vertical axis of the limb when the whole hoof and the coffin joint is equally and evenly loaded.
In an optimal limb the back of the hoof is strong and deep, ie the lateral cartilages are thick and not deformed, the frog pad is deep and strong, the digital cushion is not degenerated into fatty tissue, the wall and bars are strong and retain vertical integrity; the suspensory apparatuses of the fetlock and coffin joints are strong and healthy, and the flexor muscles are strong and healthy and in balance with the extensor system.
If the limbs of the horse are in optimal condition from ground to spine and the stride is normal, why would the coffin joint with a GP pedal bone over extend under load?
The fetlock and coffin joints have sesamoids to increase their surface area - to spread load and to enable them to go through a greater range of motion. The fetlock joint has a far greater range of motion than the coffin joint obviously and has a complex system of back up with first the superficial digital flexor tendon and then the deep digital flexor tendon coming into play with their respective check ligaments that serve to protect the belly of their muscles.
Problems for the suspensory apparatus of the coffin joint arise when the stay apparatus is compromised by persistent misalignments, and / or the back of the hoof is weak.
A common example of a weak caudal region is a long but low heel (underslung); deformed, splayed bars; deformed and thin lateral cartilages; thin prolapsed frog; degenerated digital cushion; compressed bulbs. Such a hoof exposes the back of the coffin joint to stresses.
But the answer to this hoof form is not to stand the pedal bone on its tip by elevating the heels, but to trim and manage the horse so it can regrow a strong heel that can retain vertical integrity.
Yep - easier said than done -and success depends on a fairly intact bone. So, the best answer is, don't let the hoof get like that in the first place!!!
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