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Sacroiliac Joints
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David Genadek
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 Posted: Mon Nov 24th, 2014 08:19 pm
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Deb, This blog is making it's way around the internethttp://www.holisticequinerehab.ca/blog/the-hunters-bump-code-words-for-your-horse-has-a-dislocated-sacrum
The author is drawing some criticism for using the term dislocation. This has stimulated some discussion on the difference between subluxation and dislocation. I am of the mind that if the joint or joints are causing a hunters bump then I would think they are actually dislocated as such I do not feel the author was out of bounds in calling it a dislocation. The nature of the Sacroiliac joints make the lines a bit blurred. How would you view the issue of subluxation vs dislocation in the Sacroiliac Joints?

DrDeb
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 Posted: Mon Nov 24th, 2014 09:53 pm
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Dave, in medical terminology there is no difference whatsoever between the two terms. Subluxation is merely Latin for dislocation. Some doctors will use the term 'luxation' as a more general term than 'subluxation.' It makes no real difference.

Chiropractors, who are not medical doctors, use the term subluxation in the sense of a 'chiropractic subluxation'. This means that the joint in question is not 'seated' correctly but is not dislocated, so it is from Chiropractors' usage that any difference in meaning has arisen. To a chiropractor, to be dislocated means that one of the bones that compose the joint is far from being in the correct or normal position for articulation. Normally this would also involve tearing of the surrounding structures, i.e. ligaments, cartilages or tendons, and hence move the injury out of the realm that can or should be treated by a chiropractor. He or she is supposed to refer such cases to an M.D.

I myself have used the word 'subluxation' to describe what happens, or what the process is, in the development of a hunter's bump. It is indeed a subluxation of the sacroiliac joint. However, in a horse that has the hunter's bump but is also pain-free and serviceable, any associated tissue damage has already healed, so that the horse has a conformation post-injury and post-healing that is different (its croup is steeper) than before the injury. Cheers -- Dr. Deb

David Genadek
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 Posted: Mon Nov 24th, 2014 10:02 pm
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So we have actually done damage to the soft tissues and thejoint has moved to a different position on the pelvis? Has it dislocated and relocated?

DrDeb
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 Posted: Tue Nov 25th, 2014 03:00 am
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Yes, that's exactly what happens. You recall from anatomy class that the Sacroiliac joints are flat, with rough surfaces; they articulate with the inner upper wings of the pelvis (the iliac wings) like miniature egg cartons stacked together. The roughness discourages sliding, but with enough transverse force it can occur.

Jeannie
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 Posted: Sat Nov 3rd, 2018 05:21 pm
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Hi Dr Deb,
I've been trying to picture what happens when a horse develops a dip behind the saddle followed by raised area that looks a bit like the front of a pup tent. Could a young horse develop this from being asked to go forward over tempo too often?
Jeannie

DrDeb
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 Posted: Sat Nov 3rd, 2018 11:07 pm
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Jeannie, what you're describing is ultimately due to subluxation at the sacro-iliac joints, but involves the sacro-lumbar joint too. The dip is due to "back strain", i.e. tightness in the longissimus dorsi muscle that overpasses the sacro-lumbar (NOT the sacro-iliac) joint. The bump is caused by the displacement, slightly forward but mostly upward, of the anterior end of the sacrum -- this is a sacro-iliac problem -- which causes the sacrum to tilt more than it was meant to, so that its  first dorsal process rises under the skin and thus changes the contour of the topline there.

Again, to be clear:  the sacro-LUMBAR joint is midline. The sacro-lumbar "joint" is actually a set of three roller-shaped articulations, all aligned horizontally, that serve to connect the sacrum forward to the last lumbar vertebra. The central S-L articulation is centrum-to-centrum, and the ones to the left and right of that connect the left and right transverse processes of the sacrum forward to the left and right transverse processes of the last lumbar vertebra. This joint complex is designed to move freely in a manner that allows the rear end of the sacrum to rise and fall on the horizontal joints at its front end, as a trap door would move when opened or closed. Its functioning is the key to collection and to all correct movement in the horse, and its triple construction is unique to horses and their close relatives.

The sacro-ILIAC joints are a pair of rough abutment-type joints which are not designed to move very much. They can rock just a bit in the younger horse, but often fuse solidly or "cement across" in older horses, causing very little noticeable difference in way of going or external appearance.

The sacral surface or component of each of the S-I joints is a roughened area on the upper surface of each transverse process. The iliac surfaces are roughened areas on the lower surfaces of each ilium. The joints are lateral to the midline by several inches, i.e. by about 85% of the width of the transverse processes of the sacrum. The sacro-iliac joints are frequent subjects of chiropracty because they can become "subluxated", i.e. dislocated to a degree; or, given the right sort of trauma, they can be frankly dislocated. This is the origin of classic "hunter bump", where there is a big, obvious, and unattractive lump.

The classic etiology for hunter's bump is luxation of one or both S-I joints through having one or both hind feet caught in something, especially if they get caught while the horse is moving right along. Classic instances are stepping unexpectedly into a hole, sinking into swampy ground and then struggling or scrambling out, scrambling up a steep embankment, getting hind foot/feet caught in a wire or board fence, or hanging a hind leg over a jump. However, you are correct that sometimes the condition arises simply from overly-strenuous work, especially if the horse is not moving in the envelope of release -- so it's not uncommon among 5-gaited Saddlebreds as well as hunters.

I think the frequency of this condition would go to zero (except for accidental causes) if riders more commonly were aware that the horse's spine is not mature until he is six years old -- in big, tall horses sometimes even later than that. They worry about the "growth plates" being "closed" in the legs, when they ought to be worrying about whether they are closed in the part of the spine that directly bears their weight, and that easily deforms under weight. -- Dr. Deb

Jeannie
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 Posted: Sun Nov 4th, 2018 01:15 am
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Dr Deb, thank you for this information. I've been looking at the diagrams in the Ring of Muscles article for a mental picture of what you describe happening to the sacro-iliac joints and the sacro-lumbar joint. I assume that once this happens, the resulting bump will always be visible.
Best, Jeannie

DrDeb
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 Posted: Sun Nov 4th, 2018 03:49 am
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Yes. The displacement occurs due to whatever trapped the hind limb under force of motion; often there is considerable swelling and pain as an immediate sequel, enough to make the horse too lame to ride. Then there is a period of healing, while there is a lot of fluid effusion as part of the body's effort to heal itself. During this period the sacrum is literally 'loose' or partly loose from its normal connections to the pelvis, and as healing proceeds and the fluid and edema abate, the sacrum may settle back into its original position (with a great deal of luck). Otherwise it will settle back into 'wherever', and that may mean asymmetry in any of the three dimensions. The least serious outcome is the hunter's bump! Because that means, only some rotation but no lateral or vertical twisting. Once the sacrum settles into whatever position it's going to occupy post-injury, it will very likely co-ossify to the pelvis and then that will be its position forever after that.

Do not let any bodyworker, by the way, tell you that they can 'reduce' or cure this. There is no possible cure, and if you do get an asymmetrical re-attachment, that's really too bad, because the animal cannot be made physically straight and will never again be able to carry itself straight after that. You may indeed need a chiropractor to help him out in that case, because his entire body will be perpetually a chain of compensations, due to the fact that the basis, where the hindlimb attaches to the rest of the body, that is to say the sacro-iliac joints, are no longer (within normal limits) 'square' to its head or forelimbs.-- Dr. Deb


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