Medio lateral balance
There is nothing more important to the horses skeleton than M/L balance in the hoof.
A limb always goes through flexoral ranges of motion with every stride from heel impact to break over the angle the horse is climbing or descending is just included in the stride of the motion. Not the same with angular changes, the hoof is supposed to travel under the body and all the joints are to line up in a straight line. The joint interfaces have ridges to limit any angular deviations, and in fact they work so well that the leg may travel in a straight line from end to end except that the foot and shoulder are offset and equal angles. A hoof may have a 10 degree lean to it, the leg bones will align all the way to the shoulder and the shoulder and elbow will adjust to compensate for the 10 degree lean at the bottom end.
The worst of these cases was a young horse so badly setup in the left fore that he would crash the left fore leg into the tendons of the right fore when walking or trotting, almost knocking himself to the ground. The frog was off center in his hoof and the whole hoof was twisted to the center line. A classic toed in appearance. It took one trim for this horse to be able canter or walk down hill. The horses leg deviation and toed in appearance were man made and left the horse unable to graze without falling forward, unable to walk down hill, the horse had to zig zag. As the motion of traveling forward could not be stopped as the DDFT was no longer behind center of the pedal bone. For a horse to slow down the body must be able to create strain in the DDFT by anchoring the toe in line with the direction of travel and have the DDFT behind that line.
I will probably sound like a machine repeating the fact that before you become a trimmer or shoer you should be a massage person. Just putting your hands on muscles can tell you what is wrong with the mechanics of a horses hoof. If you don't want to learn to massage find your self a good one who understands your work and is happy to pass on their knowledge.
Most conformation faults published in books are usually published with their corresponding hoof deviations that causes those "Posture" faults. You can sometimes see a hoof deviation from 300feet away as the way a horse body looks is linked to its feet. You can easily correct toed in or toed out so called conformation faults as well as many flexoral faults by understanding how the horses body is driven by the position of its feet.
I once went to a Pete Ramey clinic in Tasmania where we were looking at a wild horses hoof with a M/L imbalance and it interestingly showed a break over off center to the true hoof but one that was mechanically based on where the imbalance forced it to be. Pete was explaining that this is never to be fixed as the way the horse moves is based on its feet and to force a change was improper and bad for the horse.
This bugged me as I had many many successes bringing these feet back to norm and providing a more sound upper body for the horse. All through while Pete was talking I was staring at the bottom of this hoof trying to fathom what Pete was saying and asking the hoof what it was saying. The bottom of the hoof did not lead to the answer as it was what every trimmer sees. The break through came when I had a brain wave that if I was right about fixing these hooves the body would have made adaptations above the hoof capsule for bad feet. Sure enough when I turned over the preserved hoof and looked at the pastern bones it was there plain as day. The bone had shifted to one side of the tissue that makes up the pastern, one artery had been pinched closed by the shift and the other artery was wide open. BFO moment if you get the feet wrong you also stuff up the upper body in ways you cannot see, do not trim just the feet look at the whole horse. At the moment too much attention is paid just to the shape of the hoof but not what that hoof is doing to the upper body. The hoof must not interfere with the upper body it must function as an extension of the body.
Once I realised the shift had occurred due to the poor hoof form, I wanted to confirm my next suspicion about where the bone had shifted to. I lined up the false breakover with a 90degree line from the edge of the bench and guess what, The pastern bones new alignment put it perfectly in the middle of the whole hoof capsule behind its offset break over. Damn clever things these horses feet, to support such a mass above them properly the hoof capsule has an equal distribution of support either side of the boney column. This adaptation is not visible in the hoof or pastern from external views but X-rays would have shown the shift in the boney column. The norm for any hoof is to be equally supported by hoof capsule either side of the boney column, all hoof carers know this in a basic sense, but to see the body try and take on a poor hoof form as a support and adapt to it is amazing and never to be misjudged as the norm for the horse.
So due to the M/L imbalance the hoof had to be rotated by the upper body to achieve a reasonable break over, to compensate for the rotation of the limb to meet the breakover the pastern bone had been pushed to one side of the tissue. These changes are in response to the problems in the hoof and impact right through out the body. When all the hoof needed was the extra toe on one side of the hoof trimmed so the body could return to its uncompensating shape.
It was so obvious that the body was under strain by something as simply corrected as a M/L imbalance in a fore limb.
Now moving onto hind limbs, these can be doozies, balance, balance, balance get them right what ever it takes.
The horse can still move if its feet have a M/L problem in the hinds and most people would be happy with that, but as trimmers we have to strive for better hoof care. My favourite local shoer is a stickler for M/L balance out of 100 feet I found one wrong. The rest of the shoers near me would not know M/L balance if it bit them.
You can see a bad M/L balance in a hind foot from 100 feet away if the horse has no rug on. The top origin of biceps femoris is wasted and underdeveloped and the gaskin is overdeveloped. You can then ask the owner if the horse lacks impulsion and has to throw themselves into a canter. The answers are always "yes, how did you know". Muscles never lie, if they are developing wrong then the hoof carer is doing something wrong.
Like the information on the bars the key point in hoof care is circulation, and compromised circulation is bad for the hoof. When looking at a hoof that is badly out of balance you have to be aware of where the blood can flow too and what the effect of this blood pattern is going to do to the hoof.
My worst case of M/L balance was 1 and 3/4 inches difference between the Medial and Lateral walls in relation to true balance, the walls themselves were probably 2 and 1/4 inches different in length. This had occurred over a number of years as the horse was a trotting racer that was being shod by the owner/trainer. He commented that the horse had a turned in hock and should always be shod that way. The horse was given up as retired as his racing career had ended early with a long slow fade off in his race performance.
Funny how the angle the hind foot was shod at equalled the lack of performance.
The lady who rescued him had been trying for 3 months through exercise to build hind quarter strength and get some sort of impulsion. When I saw the horse it was a shock to see a hoof so far out of whack, I had to try and determine how it got like that. The story of a race horse getting slower than being dumped fit the profile of the damage. So my next question was how to fix it, I knew I would have to leave the lateral side untouched as I had guessed the sole was a couple of mm thick. The medial side was the question mark, I first trimmed to so called live sole but this was only taking a few mm of junk off the top. So what now? I checked the depth of the collateral groves and found there was a massive difference. This gave me the confidence to look at the so called live sole in a new light. There must be too much sole but how much. I trimmed and shaved and checked and trimmed some more. I must have removed and inch of so called live sole without getting close to drawing blood. This still left the hoof 1/2 inch out of balance but this was better than 1 and 3/4 inches.
I checked with the owner later to find that within a week the horse had developed muscle and gained a huge improvement in impulsion.
Success, but on my return the foot was headed back to the other angle, why and what was going on. The key is balance and circulation. The hoof is getting the stimulation of hard work but due to poor circulation under the side that the boney column sits above, most new growth goes to the side of better circulation and due to the lack of weight over there the sole grows well and thicker. This further starves the overloaded side of growth. On the third trim I looked at an overgrown spot on the lateral side and decided to have a poke at it to see if it was interfering with the blood vessels underneath. I removed 1mm of overgrown tissue and noticed bruising and red underneath this meant the sole was only mm's thick. I then continued to trim away so called live sole on the medial side to bring the hoof back into balance. I could in theory trim the medial side to be the same thickness as the lateral side to speed up the healing process. I feel that is dangerous as the hoof is already damaged by those that think the live sole is the limit to trim too, there is no need to push the trim beyond a standard sole thickness. It would also be difficult to gauge the depth of the corium not under pressure compared to the one that is.
This deviation in sole growth is important to consider for all hoof repair. Areas of excess ground contact do not heal as well as those with correct ground contact. So yes trim that lumpy sole or bar because we know that the pressure restricts vascularisation and circulation. This reduces the repair to an area and also creates inflammation in the hoof capsule, creating on going damage to the whole rest of the hoof.
Remember also that a horses limb has no real capability to move outward from the body and even the farrier pulling the leg out to work on it can do serious damage to ligaments. If a horse has to deal with M/L deviations every stride it really breaks down muscle tissue and puts ligaments under serious strain. The horse with the long medial toe on the left fore had been left that way due to the shoer trimming to a false live sole plain. The recognition of how much live sole to trim was all that the horses need to be able to move like a horse. This 6 year old was unable to canter in a dressage test and was unwilling to exert any effort when ridden. 3 weeks after his first trim was a dressage test in which he cantered and bucked around the arena. Not a good way to score, but a good example of a young horse with many more years ahead of him.
I was not going to describe how to see M/L imbalances due to the worry that some well meaning horse owner would try to trim their horse wrong. With so many horses wrong out there I will ask the beginner not to do the trimming but still look for the imbalance so they can let their trimmer / shoer know.
The way to find a M/L balance issue in the front feet is to hold the forelimb in a naturally flexed position under the body then supporting the fetlock but not much support of the pastern push the foot forwards and backwards under the horse in a straight line using the canon as a guide to the center line of the hoof. As you shift the leg back and forth in a straight line look for which part of the hoof is longest and run a 90degree line to the canon bone from here. This in theory should reach all parts of the hoof at the same time. Now with your finger tips tilt the hoof up and down while holding the leg in the same straight line. You should see heels of equal height and then as the foot tilts the front of the hoof should appear like a sunrise with equal parts either side of the center line, and in line with the 90 degree line.
WARNING if you use the leg to align the hoof make sure the horses head is straight ahead of its body, as the horse looks to the left or right it causes the M/L balance to shift in preparation for the horses body following the aim of its head. Quite a nice feature of bio mechanics of motion but a trick for unwary trimmers if the horse likes looking to one side while being trimmed the hoof will be trimmed wrong. This also means that the area you trim in should be setup so the horse has no inclination to look to one direction.
Hind leg M/L balance is very similar to foreleg balance though the range of error can be much greater as the hind legs are attached by one ball and socket joint rather than a mass of muscle like the shoulder. So the deviations can occur easier and more extreme than in the fore limbs. With the horse relaxed support the fetlock and extend the leg backwards in a straight line behind the horse and back below the rump, the horse may tense at first as his balance shifts with your movement. Once the horse is happy with your grip you will notice the same things as with the foreleg, the heels should be level and at a 90 degree plane to the leg. Then tilt the hoof up lightly with your finger tips to see what angle to toe comes into view over the heels.
Remember you are only doing this to see what is wrong with the hoof not to trim it unless you are well trained in hoof care.
I remember Pete Ramey stating that you should never balance a foot from a coronet, especially by standing the horse on concrete as you will do damage to the horse. He is right and wrong, the reason why he is right is that the coronet should never be used as a guide to where the pedal bone is within the hoof capsule. The reason he is wrong is the same thing, you can get a clearer picture of how a horse moves or stands if it is on concrete. The concrete is your best friend as every mm of incorrect hoof trimming can mean slow changes to the muscles in the upper body. The coronet can be trained to return to its correct level by proper trimming, do not align the hoof by the coronet but align the coronet by the hoof.
I have seen X-rays showing how correct trimming of the M/L imbalances can achieve proper upper body health, the X-ray shows the differing thicknesses of sole medial to lateral and how the pedal bone is tilted with in the hoof capsule.
Remember the upper body can tell you when you get it right or wrong in the hoof.