welcome back to anatomy and physiology on catalyst University my name is Kevin toke off please make sure to like this video and subscribe to my channel for future videos and notifications in this video we're gonna be talking about the sacroiliac joint or SI joint and in addition to that we'll be looking at a bunch of other pelvic ligaments some of these we'll see in a later a set of videos when we talk about the iliofemoral joint or the hip joint but in general what we're talking about here in the next few videos are joints that are associated with the pelvis and when we talk about these joints we have to be very specific about which joint because there's a lot of joints here and they all do different things and all have varying degrees of motion the one we're talking about here is the sacroiliac joint this is a joint between the sacrum which is right here and the ilium okay on either side so there's two sacroiliac joints okay if we're talking about the iliofemoral joint which will be in future videos maybe a few from now that's the hip joint but there's also joints let's say between the sacrum and the coccyx there's joints between the ilium and the ischium so we need to be very specific here this is the sacroiliac joint now the sacroiliac joint is a low mobility synovial joint between the two ilium x' or Ilia right here and the sacrum and the one thing I want to really emphasize here and we're gonna hit this more in the next video is that this is a very very low mobility synovial joint it's still a synovial joint but it is very low mobility it is designed for stability can you consciously really move your sacroiliac joint do you know how to do that probably not it's probably not something you can think about because even though it's a synovial joint it's such low mobility don't even know how to do it okay very very stable and in the next video we'll be talking about why that is we'll also see we'll see later on in this video and also the next that the actual surface area of the SI joint is extremely small okay now when you're looking at this doing let's say this one right here which would be the patient's left sacroiliac joint it would be a joint between the left side of the sacrum and the left ilium the sacral side of the joint that is the sacrum is lined with hyaline cartilage in contrast the iliac side is lined with fibrocartilage okay so both sides of the joint are actually lined with a different type of cartilage which is interesting and before we go any further with the sick or iliac joint let's actually label some structures here to get a feel for where everything is okay so first of all with the pelvis here's the ilium right here all right the ischium would actually be sort of on the inside here then of course down here is the pubis all right this hole right here this is the obturator foramen but in real life it's not just a hole it's actually lined with a membrane as you can see right here this is the obturator membrane and if you look really carefully there there's a tiny hole there on the superior side of the foramen and that's created by an inconsistency in the obturator membrane that's intentional this is called the obturator canal okay and this obturator canal provides a site for some things like the obturator nerve to actually exit through okay so obturator canal obturator membrane within the obturator foramen okay right here in the dead center in the midline this is the pubic symphysis recall that's a cartilaginous joint of fibrocartilage specifically that links the left pubis to the right pubis now the first ligament we're going to look at right here is this small ligament which is the iliolumbar ligament this is an accessory ligament to the sacroiliac joint it does provide some stabilization really because it's connecting the l5 vertebra really it's transverse process ultimately to s 1 which is the superior part of the sacrum so here's the left iliolumbar ligament here's the right Ilia lumbar ligament you can see that the iliolumbar ligament not only is going to connect with the s1 part of the sacrum but it's also going to be blended with this other ligament on the anterior surface of the pelvis called the anterior sacral iliac ligament you can see these fibers are going to be running transversely across the sacroiliac joint they run horizontally between the ilium and the sacrum so the anterior sacral iliac ligament as you can see here transverse or horizontal fibers that support both the anterior and inferior portion of the SI joint you can actually see some of those right here as well they're in a little bit of a different position than these up here but they still run horizontally from the ilium to various parts of the sacrum so all of this is the anterior sacral iliac ligament and then the iliolumbar ligament partially fuses with that anterior sacral iliac ligament okay now within the pelvic Inlet right here we can see the Sacro tuberous ligament and the SE Crispina seligman so let's take a zoom in look at this the one that's a little bit more anterior is the sacral spinous ligament okay this one connects the sacrum ultimately to the ischial spine which is where it gets its name sacrum spinous ligament this one that exists a little bit posterior to the sacred - ligament we can see a little bit of it here this is the sacred tuberous ligament it connects the sacrum to the ischial tuberosity again where it gets his name over on this side same thing but what I want you to notice here is if you look at the anterior one which is the say crows - ligament notice that the way it's fibers run they run a little bit more horizontally it's still diagonal but it's more horizontal than the posterior one the sacred tuberous ligament it's fibers run a little bit more seemingly inferiorly okay so they run at different angles and that's another way that you can actually tell the difference between the two this is an anterior view of course so the one in front is sacral spinous the one posterior that one's a little bit more inferior Lee Sacro - Burris okay now let's take a look at these ligaments which are actually ligaments of the iliofemoral drink we'll see these in about two or three videos from now this one is called the Y illegitimate because it actually splits up into sort of a Y shape if you were to turn the Y upside down this is the iliofemoral ligament as I mentioned also called the wild Lichtman it has two part has a thinner part which runs a little bit more inferior Li or vertically I should say and then it has another part which runs a little bit more horizontally than the vertical part right here both of these constitute the Wai ligament more properly called the iliofemoral ligament okay and then this one right here that's more medial we can see it on this side as well this is the piu both amoral ligament again named that way because it connects the pubis to the femur okay so q both femoral this one is iliofemoral because it connects the ilium to the femur hopefully that makes sense one other thing I wanted to mention about the sacral - ligament before we go to the next slide remember that was this one right here that connects the sacrum to the ischial spine which we can't really see there it helps support the sacroiliac joint mainly by preventing upward movement of the sacrum okay that's a motion called nutation and we'll be dissecting that motion a lot more in the next video but it's suffice it to say that nutation is restricted by that Sacro spinous ligament okay and again remember it's anterior to the sacral tuberous ligament join us in the next video when we actually talk more about that now the posterior view of the pelvis and really the sacroiliac joint so here's the sacrum right here here is the ilium this is actually the posterior side of the iliac crest okay and we can see here the left sacroiliac joint and the right sacroiliac joint we can see the obturator membranes actually posterior lis but notice that the sacred tuberous ligament right here is actually covering those can't actually see all of it so here's the obturator membrane that's filling up the obturator foramen there's of course a little obturator canal therefore the obturator nerve lots of operators right and then we can see here a good look at the Sacro tuberous ligament okay sacrotuberous ligament remember is going to be connecting that sacrum to the ischial tuberosity which is down here okay so that's the sacred tuberous ligament that is the right one we can actually see the sacred spinous ligament I didn't label it look a little bit of it's actually right here because this would actually be where the ischial spine is and we can see that this one if we were to continue it underneath here because it's more anterior it'd be connecting the sacrum to the ischial spine so this is a little bit of the sacred spinous ligament right there again remember the sacred spinous ligaments a little more horizontal secret tuberous is a little more in running inferiorly or we could even say vertically and if we consider the sacred tuberous ligament it also helps support the sacroiliac joint by a similar mechanism preventing upward movement or nutation of the sacrum again remember sacred tuberous ligament is posterior to the safe house - ligament up here we can see the Ilia lumbar ligaments posteriorly remember that those connect the l5 transverse processes not only to the anterior sacroiliac ligament but also to the ilium itself and they indirectly help stabilize the SI joint here is the posterior sacroiliac ligaments this is something that can be a little bit confusing here because it actually is split into two regions one thing I want to mention is that posterior sacroiliac ligaments or ligament as they'll sometimes call it collectively is also called the dorsal sacrum iliac ligament okay dorsal is also common to see here and that's important because the two subdivisions of it we usually use the term dorsal a little bit more frequently now in general the dorsal or posterior sacroiliac ligaments they're composed of short and long fibers that connect the sacrum and ilium posteriorly so they're really serving the same function as the anterior version but they're on the back side so first of all let's talk about the short dorsal sacroiliac ligament and where ligaments that's this region up here so pretty much where I'm tracing with my mouse everything bounded by that that is the short dorsal or short posterior sacroiliac ligament you can see these ligaments again run a little bit obliquely but they're more horizontal than this one right here which I'm going to get to in a second so in this region these are the short dorsal sacroiliac ligaments notice that for the most part they really just go around the sacral foramina foramina okay and they connect the sacrum to the ilium posteriorly now this one right here that resembles a little bit more of a ligament in the sense that it looks like a rope this is the long dorsal sacroiliac ligament is still connecting the sacrum to the iliyan right here via the most posterior part of the iliac crest but it also partially fuses with the sacred tuberous looking at which we can kind of see here there's our secret to wrist ligament here's the long dorsal sacroiliac ligament where does the long dorsal sacroiliac ligament and and where does the sacred tuberous ligament begin who knows they're mostly fused with each other kind of in this area right here okay but this is the long dorsal sacroiliac ligament this region is the short dorsal sacroiliac ligaments and collectively they are the posterior sacroiliac ligaments or dorsal sacroiliac ligaments hopefully that makes sense to you and there's one more set of ligaments here that we can't see we'll actually see them in a couple of slides and those are the interosseous secret iliac ligaments we would actually have to peel off the posterior sacroiliac ligaments here to see them because they're deep to them and basically what they do is they're a set of massive strong ligaments that unite the sacrum and the iliac tuberosity x' okay so they're gonna be kind of underneath really the short dorsal sacroiliac ligaments we'll see those in a couple of slides okay now here's what I want to do here's the original view of the pelvis that we saw what I'm gonna do here is I'm gonna take a cross-section of the SI joint which is kind of right in this area right here I'm gonna take a cross-section of it and then I'm gonna look down from the superior aspect of that cross-section okay and that's gonna give me this okay so right here we have the ilium okay here's the superior view of the cross section of the sacrum you can even see the sacral canal right here which remember is where some parts of the cauda equina are actually going to move through as they descend inferiorly you can see the sacrum kind of curving anteriorly and terminating at the coccyx right here and now let's fill in some other features here here's the ischial spine so this region is the issue of course so that makes this ligament right here the Sacro spinous ligament because it's connecting the sacrum to the ischial spine Sacro spinous the one posterior to that right here or on this side Sacro tuberous ligament because it'd be connecting the sacrum to this region right here which would be the ischial tuberosity right now for the SI joint here is the sacroiliac joint on the right side here's the left sacroiliac joint notice that the surface area of this is very small remember that the sacral end is actually lined with hyaline cartilage the iliac end is lined with fibrocartilage and then these two surfaces contacting each other constitute the SI joint we can see a little bit of the anterior sacral iliac ligament on this side right here because this is of course the anterior surface and then on the posterior surface we can see a little bit more at this level here's the superficial posterior sacroiliac ligaments of two parts short and long dorsal sacroiliac ligaments and then deep to that we have the interosseous sacroiliac ligaments okay remember those are deep to the posterior and so we'd actually have to peel off the posterior sacroiliac ligaments to see those interosseous sacroiliac ligaments now right before I conclude this video I want to mention something about the position of the sacrum right here okay the sacrum sits right in between the left ilium and the right ilium if we go back to this view yeah there's some ligaments here but keep in mind we have all the vertebra right here and all the weight of everything above that you have the weight of the torso and the abdomen everything inside all the bones there and muscles you got the way to the arms all the bones all the muscles the head the neck everything how the heck does the sacrum just not fall through with all the weight how is it that these ilium left and right are able to just hold that sacrum in there because remember this joint is really small and surface area how the heck does the sacrum actually just sit in there even with all those ligaments are they just ultra super man strong ligaments or there's some other factors that make this joint so stable it turns out there's a lot of other factors that make this joint stable other than the fact that you have a bunch of supporting ligaments and they are strong but the ligaments by themselves in their natural state would not be strong enough were it not for another a number of other factors that actually stabilizes SI joint think about it how does this sacrum just sit there with all the weight on top of it all the time if you're jumping doing a high jump and then you land how the heck does the sacrum not just fall through we're going to be discussing that and a few other things in the next video please make sure to LIKE this video and subscribe to my channel for future videos and notifications thank you