hey guys so this is biomechanics and kinesiology of the sacroiliac joint so what are the functions of the sacroiliac joint of course it acts as a link in between the axial skeleton the spine and the lower extremity it's responsible for transmitting all the forces from the upper extremity to the lower while standing and transmitting forces from the upper extremities and the axial skeleton to the ischial tuberosities while sitting the bones that comprise the sacral iliac joint provide an attachment science for of course for multiple key and large muscles of the trunk and low extremities and one of the main functions of the sacroiliac joint is to absorb the ground reaction forces in standing and sitting activity so remember as we spoke about in one of the first classes for every action there is an equal and opposite reaction so once again we're keep hearing about the ground reaction forces anytime our foot touches the ground we have a force going from our foot into the ground and of course there is an equal and opposite force coming from the ground to our foot so they're important to remember we're gonna talk about it in posture and gait lectures as well so once again as I joined responsible for transfer of forces we have transfer of forces from in standing from lumbar spine to sacroiliac joint to ilium two few more assertively joint and down to the ground and in sitting the forces being distributed from the lumbar spine through the sacroiliac joint and down to the ischial tuberosities right here to the chair so Anatomy review we're gonna be looking at the whole pelvic complex so it's not just the sacroiliac joint as a therapist you have to appreciate the complexity of the whole pallet complex so of course it's composed of the two environments on the right and the left one we have the sacrum sitting right here in between an l4 l5 just above the sacrum in terms of joint we have the sacral iliac joint number and number to the right and left we have those pubic symphysis right here symphysis pubis joined and that is a cartilaginous joint in between the two nominates we have articulation between l5 and s1 which we mentioned in the lumbar lecture but we'll go over that one more time and of course we have the acetabular femoral joint and we covered that in the hip lecture of course as you think about the function of the sacroiliac joints you're gonna think about the need to transfer forces as we mentioned the second ago so we will require advanced and complex ligamentous network in order to stabilize the joint that constantly is responsible for force transfer from the superior body or from the ground reaction forces that are acting upon it so the muscles in the sacral and lumbar plexus are not something that we're gonna be looking at in this lecture okay so the sacrum itself so the sacrum is the triangular bone right here right it's made out of the five fused bones as one through as five it has a base and you have to remember that the base is superior and the epochs is inferior right here around the inferior portion of s5 so the interior surface is right here and the posterior surface is showing on the right the interior surface is smooth in the concave of course allowing the organs to sit on the inner side of the pelvic ring and the posterior side posterior side of the sacred ilium the sacrum is not smooth of course and that is of course for attachment of the various ligamentous networks and muscles the lateral surfaces are the auricular surfaces so they're located right here and there Ralph and articulating with the two innominate so the superior surface accesses that superior articular processes so these are the superior articular processes articulating with l5 so was inferior articular processes of l5 we also have a sacral base which I mentioned earlier so it spans from the most lateral sites to the other most lateral side of the sacrum the reticular surfaces their articular facets face close to posterior and slightly medial and we spoke about the frontal plane articulation of the facet joints and we'll mention it in a few slides again so it's important to note the location of sacral promontory so it sits right here as we gonna dive into the biomechanics of the sacral joint you're gonna notice that we refer to sacral promontory going anterior or posterior so it's important for you guys to know where it actually sits lumbar facet joints so just a second ago mentioned the art of the orientation of the sacral facet joint so this is orientation of the lumbar facet joints so we know that the inferior articular process of the superior vertebrae right so inferior articular process of the superior vertebrae articulates with the superior articular process of the inferior vertebrae rain so that's what I'm showing here l4 articulating was l5 so the general consensus is that l1 through l5 is typically in line with the sagittal plane so we can see the facet orientation right here and it's more in the sagittal plane but as we get down lower we get closer and closer to the frontal plane and here you can really see it clearly the orientation of the joint in the frontal plane right so that's gonna be important for the stability of the sacroiliac joint so the superior of a set of l5 faces posteriorly right so we can see the superior facet of l5 facing post early and the inferior facet about l5 all faces close to interior and slightly lateral so this is the inferior facade we can see how it faces in turn slightly lateral in order to meet the medially orient secret facades so lumbosacral junction is a transition zone from one region of the spine to the next and transition zones it's typically the frequent areas of pain and dysfunction in the body so lumbar sacral Junction is composed of the intervertebral discs just like any other lumber joint right so we have the vertebra disc and the vertebra articulating it well in this case it's gonna be the base of the sacrum and post early we have two joints articulating together once again it's two facet joints they're plain synovial joints and gliding will be allowed that these joints so the inferior facet of l5 which faces interior to slightly lateral which I mentioned the slide ago will be articulating with the superior of a set of s1 right here right this is the superior of a set of s1 which faces posteriorly to slightly medial okay so now we're gonna take a look at the iliolumbar ligament so you guys probably remember from Anatomy so aliyah lumbar ligament starts from the transverse processes of l4 and l5 also adjacent fibers of quadratus lumborum and inserts inferiorly right here to the ilium just interior to the sacroiliac joint so the they attach to the upper lateral aspect of the sacrum so the function of iliolumbar ligament is to actually stabilize the lumbar vertebrae and prevent the entry and rotational translations of the l5 and s1 so basically stabilize l5 in multiple directions on L on the s1 so we're going to take a look at poor stabilization in just two slides of the iliolumbar ligament a ll so once again we mentioned a number of times starting from the cervical spine to the lumbar spine and it extends down all the way to the lumbosacral Junction right here so it starts from the bezel apart of the occipital bone and inserts goes through interior surfaces of all the lumber vertebras right here it starts off thinner and environs as it goes down closer to the lumbar spine and once again it has to reinforce that lordosis created by the lumbar spine the fibers of the interior longitudinal ligament also blend into the interior portions of the disk so it creates reinforcements of the disk upon on the vertebra so it's why is that the tensile strength of the PLL that runs that's really thin in the lumbar spine as we mentioned so once again the function is to restrain extension in the lumbar spine and to resist excessive lumbar spine lordosis so it also acts as a passive barrier to resist excessive in syria shear for is that acting upon all on all the vertebrae and the sacrum so we're gonna mention enter you share but i just want to just show you what i actually mean so the answer is shear force is going to be simply an interior translational force of the vertebra upon the inferior portion of the other vertebrae or the sacrum in this case so interior of l5 would be interior translating translation of l5 on s1 now we're going to dive into it right now so lumbosacral angle is something that i mentioned in class and I mentioned spondylolisthesis in class as well but we're gonna go over it again just to make sure that you guys have the slides so lumbar cycle in angle is the articulation in between l5 and s1 and the angle that's created in between the two vertebrae you can see there is a certain calculation that you have to do in order to actually calculate the angle but the base of the sacrum is naturally inclined entirely right you can see how the base is slightly more in Syria than the the vertebrae right here and this inter inferior orientation of the sacrum forms the 40 degree angle and standing of the l5 and s1 Junction so the body weight that comes from above essentially creates shear force so there's constant shear force going I'm just gonna put the line and again for you so there is a constant shear force of l5 trying to translate forward on s1 so a typical 40 degree angle will produce an interracial force of about 64 percent of the body weight so if this angle right here increases to about 50 degrees meaning that the sacrum will rotate more and the angle will increase the forces that are translated that are acting upon l5 on s1 will be increased about 82 percent so the shear forces of translation the body's weight will naturally push as one interiorly right here on sacrum and that is of course is not good for our body so the reason you see 64 percent is a very a lot right so this is the reason why we have that frontal plane articulation of the right here the frontal plane articulation of the joints this is the mechanical blockage of the of the l5 on s1 right that doesn't prevent if you can see if l5 wanted to translate forward on s1 it wouldn't be able to because there is a mechanical stop of s1 superior facets also as you notice there is this anterior longitudinal ligament that's gonna prevent l5 sliding forward so that's an important fact to note so lumbar sacral angle so their orientation of l5 and s1 facet joints near the frontal plane I'm ideally situated to resist the inter this year right so additional passive stabilizers would be the a ll just like I mentioned a second ago and the iliolumbar ligament so unchecked answer a shear can lead to what condition and I'm that's something I mentioned in class it's gonna lead to a fracture of pars or articular s so the area in between the superior and inferior articular processes of the vertebrae and this will essentially create the condition known as interior spondylolisthesis or typically just refer to as spondylolisthesis of l5 and s1 so once again i'll show you the angle right here so if you take a look at the MRI you see how the vertebral bodies are all kind of lined with each other so here's the vertebral body another vertebral body l4 l5 right here but if you take a look at the sacral base right here and l5 you will notice this little space right here in between l5 and s1 right in this very little space right here that's not covered so this piece is essentially the slippage of l5 and s1 so because alpha I was translating forward because probably of increased lumbosacral angle for stabilization from anterior longitudinal ligament and possibly anatomically oriented facades more in the sagittal plane rather than the frontal plane created this condition where l5 will be slipping on s1 and creating this it's about 25% slip over the vertebra on the sacrum so this is just the condition to note you guys will come across spondylolisthesis and many other classes but it's important to know so let's take a look at sacral le joint ligaments so sacroiliac joint is the rigid articulation right so you have irregular rough articular surfaces of the sacrum articulating was irregular rough articular surfaces of the ilium but it's important to remember that the sacroiliac joint actually sits in the vertical plane right so there is some sort of translation happening through the sacroiliac joint and because of that we do we need that extensive ligamentous support so the sacral base is covered with Highland cartilage the ilium is sorry not the sacral base the sacral articulation was the ilium is covered with articular cartilage and the ilium is covered with fibrocartilage the joint capsule is present in between the two joints the sacroiliac joint and there is no wheel fluid inside the joint capsule as well ligamentous support of course there is extensive ligamentous support so we have three primary stabilizing ligaments of the sacroiliac joint we also have three accessory stabilizing ligaments of the sacroiliac joint so the three primary stabilizing ligaments would be the anterior sacral iliac joint the posterior sacroiliac ligaments re and the interosseous sacroiliac ligament the three accessory stabilizing ligaments would be iliolumbar ligament sacred tuberous ligament and sacral spinal segment so let's take a look at each one and detail also injury sacroiliac ligaments of course just as it sounds it's right here highlighted in pink so we have multiple fibers spanning from the sacrum onto the ilium and it's on the interior surface of the sacral iliac Junction so basically what the answer is sacroiliac ligaments is a thickening of the interior joint capsule and it was a separation of the sacroiliac joint so once again here the separation forces of the ilium where it's ago and one day action and the sacrum were to go and opposite direction okay so that's what this ligament exactly resists okay so the posterior sacroiliac ligament it's much thicker than the entry sacrum iliac ligament they're short and long fibers of the posterior sacroiliac ligaments short fibers it's a big lead deeper so this is the posterior sacroiliac ligament and we have more extensive network right here so the short fiber is I deep and they start off from PSAs and go to s1 and s2 and the long fiber is started from PSS and go to s3 rs4 lower down to the sacral apex so the function the function of the sacred Ilia of the posterior sacroiliac ligaments are very important by the way they're also called the long dorsal ligament so posterior sacroiliac ligament is also known as a long dorsal ligament or posterior sacroiliac ligament as I presented here so the function so both ligaments the deep and the long fibers become taught during counting mutation of the sacrum we're gonna go over the motions of the sacrum but for now you need to know that it becomes thought with counting mutation both fibers will resist excessive counting notation of the sacrum once again very very important to know and we'll go over the motions in a few slides once we do biomechanics so counter mutation is resisted by posterior sacroiliac ligaments their posterior sacroiliac ligament is placed on slack during mutation motion of the sacrum okay so once again we'll take a look at the motions in a few slides interosseous ligaments self-interested segments little ligaments that span from here to here you can see multiple fibers rain so it's a collection of short and very strong ligaments that fill in most of the relative of the relatively wide gap that exists in between denominates and sacrum it acts as an interosseous membrane or syndesmosis between the innominate s-- and the sacrum and it strongly binds denominates to the sacrum so once again it resists that separation of the ilium on the sacrum now we're gonna go into the three accessory ligaments so we have the iliolumbar ligament that we mentioned earlier we have the secret to breast ligament and the sacral spinal segment so let's take a look at these so the secret tubule is ligament is right here secret to breast agreement so it spans from the sacrum onto the ischial tuberosities so this is it right here in sacred to breast ligament it's a large ligament and essentially it blends with some fibers of the superior ligament right here some of it go all the way up to PSS they spend from the lateral portions of the sacrum and inserts onto the ischial tuberosity the fibers blend was by Sophie Morris and posterior sacroiliac ligaments and some of the fibers also blend was a gluteus maximus in the posterior section right here so the sacral spinal segment it's right here so it starts from the it's deep to the secret superest ligament as you can tell this is the sacred tuberous and this is the sacral spinous ligament so it's lateral coral and of the sacrum and it goes to the ischial spine so it shall spine right here both sacred tuberous and secrets - ligaments so number one and number two they both resist mutation okay send you of the sacrum is resisted by sacred tuberous and say cross - ligaments important to know some mutation of the sacrum okay will be sacrum we're gonna go over it in in a second but I'll just cover it right here just so you guys know nutation of the sacrum is the sacral promontory right here going interior and thus if you can imagine the sacral promontory going in serum the apex of the sacrum right here will be going posterior so we'll be going and opposite direction so it will be going upwards like that so the sacral promontory will be going interior and the ebooks will be going posterior superior okay so this motion is called counting mutation and as you can tell if the apex is going to be going upwards right and back these two ligaments the sacral spinous ligament and secret tuberous ligament will prevent the e packs of going in that direction so these two ligaments once again they're responsible for preventing mutation motion of the sacrum so finally that let's take a look at the kinematics motions of the sacrum so sacrum is one of the most difficult joints to assess in their entire body the sacral iliac joined typically reported to be a source of being in about fifteen to thirty percent of patients with chronic lower back pain so there is a bunch of different-sized that you guys will learn through the program that you can use as a cluster of tests to assess the sacroiliac joint there is also ligament the stability test that you guys will learn but these are some typical tests that are presented to you in physical therapy school that i used to assess the stability of the sacroiliac okay some motions of the sacrum within the sacroiliac joint it typically occurs on the medial to lateral axis of rotation the location of which has yet to be conclusively determined the amount of motion and the typical circumstances is very very small so that's why you know some physical therapy schools they argue that it's impossible to assess the motion of the sacroiliac joint with manual palpation while other schools of thoughts they think that you can actually palpate the sacroiliac joint it really depends whose research you look into but the typical ranges of motion for sacral rotation would be one to eight degrees of total rotation so that's very small right and it ranges from point five to about eight millimeters of translation in motion so the physiologic and clinical significance of sacroiliac joint motion has been in the mean ignored by all except for OBGYNs right and clinicians who actually regularly deal with Society syndromes so sacroiliac joint is very interesting joint for for you to look in so of course if you go in into orthopedics or if you're going into pelvic floor as a manual therapists sacroiliac joint has a lot of biomechanics and Anatomy to explore so that would be an interesting joint to look into later on in life so sacral motion finally we get into it so like I mentioned there are two typical motions of the sacrum there is nutation motion and counter mutation so nutation means to nod rights of the sacrum you can imagine is nodding forward right mutation to nod so the base of the sacrum will tilt anteriorly and slightly inferior while the apex of the sacrum will move posterior and slightly superior okay the sacral promontory like I mentioned earlier will move in serially okay so just spatial orientation for you counter nutation will be the opposites concentration will be the base tilting posts early and the apex moving internally and slightly inferior right the sacral promontory will be moving posterior so once again mutation means to not the sacral base will be going internally counting mutation is the sacral baby's moving post early on the ileum so signal motion is also associated with the innominate motion so we're just gonna layer on top of the knowledge that we received just now so notation means to nod the base will be going in Turley and slightly inferior the apex will be moving post early and the sacral promontory will will be moving into early mutation of the sacrum occurs was a posterior tilt of the nominates on the stationary femur so this is obviously mutation rate the base is going interior and you can picture how the sacrum is moving in Turley right here the base of the sacrum but the innominate will actually be moving post early so whether it's a relative motion meaning that the sacrum is moving and the ilium is stationary or it's an actual motion of the sacrum moving forward and the ilium moving back either or neither or case you will have the sacrum moving in one direction and the ilium moving in the opposite direction so counter notation will be the opposite so counting notation is typically associated with anterior tilt of the innominate on the stationary femur okay so if the sacrum will be going into counting mutation the base of the sacrum is moving post early tilts in posterior the ileum will be and the innominate the whole denominator will be creating an anterior pelvic tilt okay so counting notation is associated with an anterior pelvic tilt so let's layer some knowledge on top of that so lumbo-pelvic readily mentioned in the lumbar spine so i mentioned during the lumbo-pelvic with me you guys remember how the spine goes forward into flexion then at some point we have the innominate following the spine and going into interior rotation of the innominate but now we know what that the sacrum is also another player in the game and what happens with the sacrum is that it goes into account nutrition right so if the innominate goes into injury or rotation the sacrum will be going into accounting mutation so the sacral base will be moving post early while the sacral apex will be moving into early okay so the ligaments that engage in the sacroiliac joint motion to control the excessive counts annotation will be the posterior sacroiliac ligaments right so we mentioned that earlier so posterior sacroiliac ligament will check count annotation of the sacrum okay so will be active during the lumbo-pelvic flexion next lumbo-pelvic extension so coming up from the lumbar spine we mentioned that the innominate move posterior and at the end the lumbar spine starts going into extension but we didn't mention the sacroiliac joint so what happens if we're thinking about the innominate moving post early we know that the sacrum will go in the opposite direction so the sacrum will actually new tate so if the innominate sar going in that direction the sacrum indicated by the red arrows right here will be going into nutation motion meaning that the base of the sacrum will be moving entirely and the apex of the sacrum will be moving postural II the two ligaments that I mentioned earlier to stabilize the sacrum from excessive mutation will be the sacral spinal segmental we remember it attaches from the sacrum to this spine of the ischial spine of the pelvis and the secret to breast ligament starting from the sacrum inserting into the shelter porosity so these are the ligaments that will be checking mutation of the sacrum so stability of the sacroiliac joint so we have stability of the sacroiliac joint can be made from two different concepts right so there is a form closure concept and there is a force closure concept you will dive into it a little bit more with other classes but this is just an introductory introductory slide for you so as you can see the shape of the sacroiliac joint was interlocking irregular surface of the ilium and the sacrum and the type of the joint the SI joint is allowed the stability to form so the form the shape of the sacral iliac joint articulating the sacrum articulating with the ilium right here will create form closure meaning the bones are have a corresponding shape to one another and the stability will allow to be form so but a second type of stability that we have is the force is coming up from the ground being generated by the muscles of the lower extremities and the trunk and ligamentous tension force the joint into being stable so all the muscles all the ligaments that run from the ilium to the sacrum or from the sacrum to the ilium will create force closure so force as of the muscle and the ligaments are creating the forceful closure of the joint will provide the extensive ligamentous support to the sacroiliac joint so we have typically the three stabilizing forces of the sacroiliac joint we have the gravity creating the stability force we have the stretch ligaments creating the stability force and the active muscle control creating the stability force so what is stabilizing force in the sacroiliac joint so typically the most stable position of the sacroiliac joint will be nutation right so we remember the nutation of the sacral base go in the interior and the apex is going posterior so typically it will be referred to as a close-packed position of the sacroiliac joint so how do we obtain mutations so in any type of closure right in any type in any type of form closure force closure we want to create mutation of the sacrum on the ilium okay so that's gonna be the most stable position of the sacroiliac joint so how is that created so first it's created by the gravity because the gravitational line runs anterior to the sacrum it will create this flexion kind of force right the nutation force of the sacral base on the on l5 and as well as the ilium as well okay so gravity once again runs interior to the sacral base and will create flexion forces or nutation forces on the sacrum number two the stretch ligaments the stretch sacred tuberous ligament and sacral spinal segment that runs from here to here will both creates the ability and the sacroiliac joint if this the sacrum is going into nutation motion so these two ligaments are responsible for stability of the sacroiliac joint and finally we have the muscular reinforcement of the sacroiliac joint we have the direct attachment of direct spine in multi fry from the sacrum to the vertebrae which could create the nutation force as you can sell to the sacrum then we have rectus abdominus which attaches of course to the pubic symphysis right here entirely after of the pubis and that will create a posterior tilt of the pelvis of the ilium on the sacrum and thus creating the nutation of the sacrum so once again the posterior rotation of the ilium is associated with the nutation of the sacrum so that's why the pool of the rectus abdominus will provide stability around the sacral iliac joint and then finally we have biceps femoris and glued together working actually together with gluteus maximus once again producing this force couple with rectus abdominus by pooling the on the ischial tuberosity producing a posterior pelvic rotation which will essentially create a nutrition of the sacrum and create a stable environment for the sacrum to live on okay and these are the references and that's it for the sacral iliac joint kinesiology