Even though we are discussing the hind legs last, they are of singular importance. Along with the pelvis, they decide how a horse is ‘geared’; high revs with a short stroke for sprinting, or lower revs with a longer stroke for dressage – and everything in between.
The LS joint is the upper most joint of the haunch, not the hip joint, and covers only about six inches of surface area. It joins the horse’s entire hindquarter to its ribcage (and thusly to its front). Think about that for a moment, the entire haunch is attached to the rest of the horse by an area the size of your hand. It’s why the loin and sacrum are often the first areas of stress and injury in the horse.
It’s important to understand how the whole haunch works as one. Tendons and muscles that run parallel with the horse’s bones create a ‘stay system’ that coordinates the opening and closing of the joints:
- If the stifle joint closes then the hock joint also closes, or if the stifle joint opens then the hock joint also opens
- If the loin coils (via the LS joint) then the stifle joint closes, or if the loin flattens (via the LS joint) then the stifle joint opens
There is no way around the stay system without causing damage to the horse. It should now become apparent why such traits as table top croup (overly flat pelvis), post-leggedness (overly straight hind leg causing open joints) and over-angulation (overly crooked hind leg causing closed joints) are serious faults in the horse.
Table Top Croup
We can see that the flat croup of this horse causes the femur to be positioned quite vertical (indeed, in a vertical position associated with a racehorse in full extension – see diagram), in turn creating a very open stifle angle of approximately 143 degrees. Imagine the amount of loin coiling that would need to happen for this horse to lower the haunch for collection. The fact is the LS joint doesn’t have that kind of range of motion. Conversely, imagine what happens if this horse flattens its loin just a little, how that will put the femur completely vertical and further open an already open stifle joint, stressing it. This horse is functionally post-legged in the upper half of his leg and it would not be a surprise if he suffered from sticking stifles.
Post-legged
Our post-legged horse has a much steeper pelvis and it’s a good thing as it puts his femur far less vertical than our first horse making a stifle angle of 130 degrees. If he had a more typical pelvic slope he’d be overly open in this joint, but as it stands he’s already got enough problems. His hock angle is a whopping 160 degrees. Note the racehorse below in full hind leg extension (via fully flattened loin and fully opened stifle) only has a fully opened hock angle of 160 degrees. The horse’s hock doesn’t, and isn’t supposed to open to create a perfectly straight leg. That means that if this horse flattens its loin just a little, which has to happen as part of normal striding, his hock will be pressured to hyperextend. The horse will try and protect himself by taking itty, bitty steps behind.
Over-angulation
This horse has a steeper pelvis as well, but also the most horizontal femur because she’s standing with the leg too far underneath herself artifically closing the thigh joint. Of course, because of the stay system that also artificially closes the stifle and hock joints. Despite that we can still clearly see that over-angulated hind legs possess more closed joints; 115 degrees for the stifle and 140 degrees for the hock – adjusted 5 degrees higher for a properly aligned stance behind nets 120 and 145 respectively. Horses built like this live with joints perpetuately a bit closed, which comes with its own stresses (and possible injuries – ie. curbs). Opening the joints would relieve those stresses, but because of the stay system the horse would have to flatten its loin along with the opening of those joints, and now you’ve got a hollow horse with trailing hocks.
For comparison sake, below are a hind limb suited to dressage and a hind limb suited to racing. Pelvic slopes are very similar, and though the dressage leg is more angulated, and the racing leg straighter, we’re not talking gobs of difference between a horse that can piaffe in her sleep and a racehorse who thunders down the track in excess of 35mph.
I included a second racehorse hind limb to look at, Secretariat. He had a steeper pelvis (about 5 degrees) than the dressage horse, but note again that the angles created are not hugely different. This should make it obvious to all, that extremes like the examples above are bad for horses and should not be perpetuated.
Lastly, take note the difference of femur to tibia bone length ratio in the dressage horse vs the femur to tibia bone length ratio in the racehorses. That is a key factor in ‘gearing’ and will be discussed in more detail in a subsequent article.
Dressage Hind Limb
Racing Hind Limb
Secretariat
jrga made an excellent suggestion that I also mark the hind leg of the second racehorse in the racing picture to show maximum folding (closed joints) of a properly constructed equine leg as a comparison to the fully extended (open joints) of a properly constructed equine leg. So here is that picture remarked. Of special note is that the pelvis and tibia become parallel, and the femur and cannon bone become parallel as a result of full and proper coiling of the LS joint. It can not happen this way for horses with non-concurrent hind limb angles, or a table top croup.
Hooves 
Regarding those funniest horse videos, yeah i agree most of those left me kinda cold.. this latest post is fascinating like all of them. i have questions though probably not good ones because i’m having trouble assimilating all the variables. i’ll try to put one question together to get started. i’m specially interested in this topic because i’m riding a young horse who i believe has some sort of hind end issues, he doesn’t have much strength coming from behind, doesn’t track up well at all in spite of being a pretty nicely built guy in my opinion. he has grown quite a bit in the last 2 years becoming quite gangly and no longer a pony. it looks to me like his pelvis is out of whack, specifically that it’s tilted forward a bit, giving a bit of a divot at his si joint with a bit of a hump in front of that si join along the spine. this doesn’t seem very uncommon so hopefully you understand what i’m describing. so what is my question… how much can ‘out of whackness’ change basic conformation/ could this boy’s pelvis be tilted forward, causing his croup to be too flat and his back legs to trail out behing him, from being out of whack/ ie with work can it be fixed/ you might have realized i have no punctuation–my keyboard is broke… hope this makes sense thanks
The hind end is complicated because there are so many variables, and because it’s where everything starts and finishes.
Simply, yes. The pelvis and/or individual vertebrae along the entire spine can be misaligned, stuck/jammed and cause all sorts of issues, preventing a horse from being able to coil its loin via the LS joint, which would obviously prevent the horse from tracking up or engaging. Usually there are muscular/nerve issues accompanying misalignments and such, so doing acupuncture/massage can provide temporary relief.
The loin should have a slight convex shape to it and the muscling of the croup should be full and round and smooth, and come forward to cover the loin and into the back. Both the post-legged horse and the dressage horse in this article show that. Any sort of lumpiness or angularity in the loin means you’ve got an issue of some sort.
It’s important to note, that an otherwise perfectly good structured loin can be stressed by things like excessive post-leggedness (or hollowness). The reason the halter horse in our article isn’t showing a loin problem is two-fold; has a really good loin and hasn’t had to do a day of work in its life – being a trophy horse protects that loin. Even if the horse was ‘used’, his hocks are likely to blow up before his loin, but that’s not always the case.
Hope that helps.
we did some work on him a week ago–acupuncture and massage, and it appeared to me that he was tracking up much better and his pelvis was rotating down in back much more… the gal that rode him agreed.. today he didn’t look so good again.
“Think about that for a moment, the entire haunch is attached to the rest of the horse by an area the size of your hand.”
This is kind of terrifying. How do horses stand up to being ridden??
Did I get it right? http://oi60.tinypic.com/2d9ze8.jpg
What are good or ideal angles for each joint?
Close enough. 🙂
You want the joint angles to be concurrent because of the stay system. Neither the Arabian nor the QH stallion have concurrent angles, which makes things even worse for them.
Well, a lot of horses don’t stand up to riding. A lot of horses are in perpetual states of discomfort and pain. It is their inherent good natures that prevent more people from dying via hoof to head.
Sigh.
You disagree?
lol, were you looking at the missing shoe and the left front foot in particular, by any chance?
@ Lady Farrier 😉
Concurrent joint angles–do you mean that you want the angles of the joints to be (about) the same?
“Relatively” close in angle (or rather falling within standard and good equine conformation range) because what one joint does, so must the other do. The operation of the stay system greatly stresses the joint that is outside of normal/appropriate equine range. IE., the QH stallion has a resting hock angle that is outside of a good, functioning equine resting hock angle, instead carrying a resting hock angle seen when an equine hind leg is fully extended. That hock angle is not concurrent with his stifle angle, so if/when he were to fully open his stifle, his hock would not be able to open equally without hyperextending.
Ah, okay, that makes sense. Thanks for clarifying that for me!
the entire design of the horse’s back indicates it wasn’t meant to be ridden. Good breeding practices and good riding minimizes the damage we can do. Good riding means encouraging collection not because it looks pretty, but because it puts the spine in the optimum weight bearing position. Correct riding also builds the big muscles of the core, stomach and interior back muscling we can’t see, and the big muscles of the butt that protect the ligaments of the back and the joints from damage. Too few people learn to ride with the goal of protecting their horse and making it stronger. They think in terms of sports, fun, things they want out of the relationship. They will pay attention to feed and safe surroundings and miss a huge part of the picture. That is why every horse should be doing the classical exercises of dressage correctly, and high level dressage as sport competition should never be the model for ‘correct’.
Great comment!
Dazy makes an appearance! Now I can see her hind end in a better light! Shes doing fantastic with the stretching, and we haven’t been riding but once, just lots of moving around and stretching. I measured her height the other day and she hits right at 15hh, but shes almost 10, I don’t have any idea where that other inch came from………….could the stretching have anything to do that? She is getting super bendy, and it seems to be doing a lot of good for her, she seems to be feeling a lot better. I jumped on her bareback the other day and she was really great. I trotted some hills bareback and she just seemed to move out much better. Were not great on the belly lifts, but you can tell the muscles are moving and lifting, but not a lot. Maybe I need more pressure? When are you going back to OK, because you should make a trip down for a day 🙂
Yes, and I should stipulate that her hind limb construction is the lesser of the evils in the article, because she still has the capability to engage, whereas the other two do not.
Glad to hear she’s doing better. As the abdominals get stronger, the back will lift less during the stretch because the horse’s posture will already be ‘up’ from those stronger abdominal muscles. That is likely not what you’re experiencing right now, it’s more likely that her back muscles are still tight.
Sorry no plans as of now to return to OK.
The way I learned to measure, do it on a flat surface right after a trim with no shoes. Measure an imaginary line from the ground to the highest point of wither. Move the horse a few steps, measure, move again and use the 3 measurements to get the correct height. I have a measuring stick with a level in it, so I can measure my horse correctly. I have never heard that the height can change with exercises, could that be possible? My horse is getting his trim Monday, I’ll measure to see if the belly lifts have made any change.
Well, I did have someone at my Dr’s. office tell me that yes, people do get taller – with yoga! I’m sure it’s just recovering height we used to have, but it kind of surprised me. So, I started practicing yoga and I can tell you that aaaalll sorts of things are better than they used to be!
BayDemon, having a bit of a problem here, had to postpone my horses trim, but I am interested in this enough to follow through as soon as I can.
OK, my old guy is no taller, but he did raise his withers during the stretch! A really good incentive to keep it up. Thanks!
as her posture improves and she starts to strengthen her core muscles and if you also work at getting her to lift the base of her neck, her withers will rise in relation to the shoulders, the muscle that holds it up will be stronger. Remember her legs are not attached by bone to her torso, only muscle power and the ligament system holds up the horses spine in front. Improve that and the horse will be taller at the withers.
Thanks for the great article. I rarely comment but have been following this blog very consistently. The bay mare caught my attention in particular as my Dad owned a mare years ago that had similar hind end conformation. It was one of those things that I never liked her conformation but could never pin point what it was that I didn’t like about that haunch, now I have something to tell me what it was I didn’t like!
So glad an old question could be answered for you, and please feel free to comment more often if the mood strikes you. Thanks for visiting regularly.
Mercedes. it seems to me that the comparative posture of the two race horses would be a good illustration if you marked the limb of both horses. The absolute healthy limit of opening of the angles of the hind leg in the first horse of the hind limb with the back ‘down’ as it has to be for the extension , and the second, captured in the maximum of folding of the hind leg with the back up, showing how full engagement at the SI joint, translates into folding and closing the angles of the stifle and hock. Looking at the backs of the horses, one can see the difference in the lumbar region in the shape of the back. Also, as the joints fold, one can see the angles align in an almost perfect parallelogram, illustrating that in a healthy leg, what the upper joint does the lower joint does when the SI is engaged.
You’re absolutely right. I shall do that and add to the end of the article.
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