not everybody loves learning about articulations but if you do chances are you're not as excited by bony fusion or cartilaginous joints as you are the diarthrosis these are these freely movable joints which we also call synovial joints because these have much more to do with how we move about in our daily lives plus exercise and sports physiology so we'll look in detail at the anatomy of a synovial joint starting with this very basic template of a synovial joint now this is an oversimplification you wouldn't actually find this in your body but it will introduce us to some important terms it also gives us a chance to do a quick review of some of the long bone morphology like I can see that there is a compact bone all around the periphery of this long bone and spongy bone on the inside sounds familiar there's a medullary cavity filled with bone marrow I can even see a epiphyseal line here remember that was called the epithelial plate or the growth plate and we were younger but once we become adults in our long bone stopped growing we call it the Epistle line last I can see here some thick connective tissue around the outside of the bone called the periosteum so with that basic morphology of bone out of the way we can start to look in detail at the actual articulation site starting with the joint the articular cartilages which we talked about before these are chunks of hyaline cartilage that are there to protect the ends of the bone I can also joint capsule which basically merges with the periosteum and this will provide some extra durable protection around the joints that's going to be a very rough and tough exterior layer but inside the joint you have a synovial membrane lining which is a very slippery and smooth lining and that just leaves a space inside this joint we call the joint cavity and that cavity is full of synovial fluid which is crucial to all of these synovial joints and you'll recall from the previous video synovial fluid has several different functions it's going to lubricate that joint to try to reduce friction it will cushion the joint and it's full of nutrients which will help nourish the chondrocytes that are in these cartilage chunks of the joint so there's some basics but things can be a little more complicated in the joints of our body meaning you'll often see some accessory structures you might have some bur say some fluid filled packets that are providing additional cushioning to certain parts of the joint you may also have menisci singular would be a meniscus which is a chunk of fibrocartilage found in the joint there may be fat pads in there for more cushioning there may be ligaments for extra stabilization and we'll look at each of those on another slide and like most places in your body they'll be the basic supporting structures nervous tissue blood vessels and lymphatic vessels so here definitions of those accessory structures we just talked about and you will find some of these or all of these depending on what joint you look at like let's now take a more detailed look at a synovial joint that we called the knee joint there is some basic morphology here like the patella and things like that but what we're really interested in is seeing that this joint does include bursae so here's a little fluid filled packet here's other little fluid filled packets there are fat pads in this joint helping provide christening inside our knee our menisci chunks of fibrocartilage supporting this joint and many different types of ligaments providing extra stabilization to the knee joint you now let's quickly mention one thing about bursae is that they can be a pretty basic little fluid filled packet but as mentioned on this slide you can see that they can form a tendon sheath so I have a picture of that I just wanted you to see how a bursa can actually wrap around a tendon to kind of cushion that because there's a lot of bones rubbing on each other in these joints so you want to make sure those tendons are also protected now if you take all of this stuff and you look at a very complex joint especially like the very freely moving humerus you can see there all these different per se and they have all these names a bunch of different ligaments and capsules and all these supporting structures so it can get very complicated very quickly we won't tackle it at this level of detail but I just wanted you to understand that it does get that complex now let's look at a few specific types of synovial joints and one thing that you want to take note of is that there's a trade-off in these joints between their stability and their flexibility of course a bony fusion articulation is very stable but not at all flexible but even in synovial joints you have degrees of flexibility versus stability and that's going to depend on a lot of structures like how the bones fit together what accessory structures are present how many ligaments are present and the muscles that span the joint and how they may be partially contracted at different times to maintain tension in the joint we can also name the movement of some of these articulations some of these joints will be non axial that's like some of the bones in the wrist that just slide over each other they don't rotate on an axis and then as briefly mention in a previous video we have articulations that are mono axial biaxial or triaxial meaning that joint can move on one two or three axes we'll talk about that as we look at a few joints shoulder joint finally we can really look at this shoulder joint it's not very stable but it's really flexible so I've never dislocated it but I know that Mel Gibson and Lethal Weapon it's always popping out as he fights bad guys that's my best story about shoulder joints I'm not sure many of you have seen they leave the weapon movies ah let me know if yours has been dislocated and in the future I can tell stories about my student whose arms are always popping out in their sockets but the other reason that the shoulder comes out so much is you know not just because it's freely movable but because it's a very loose fit in a shallow v remember the glenoid cavity is that part of the scapula that makes the articulation but it's not like it's wrapping around the humerus head it's really quite a shallow articulation so that's just another reason that there's a lot of movement allowed in this tri-axial joint but not a lot of stability and again tri-axial three planes of movement meaning that my humerus can move up and down it can move left to right and I can rotate it in the socket that's tri-axial joint is very stable think of that alna remember it has the u-shape at the top and that bites on the trochlea of the humerus so it's a very deep and stable connection between those bones and there's a thick joint capsule and lots of ligaments that are supporting that articulation so the elbow is uniaxial all right you just creeks back and forth I can't rotate that joint and I can't slide it back and forth I can pronate and supinate my forearm we'll talk about that in the last video in this series but my elbow joint isn't really moving when I do that hip joints that's another tri-axial example it's a pretty deep socket of the head of the femur femur in the acetabulum of the hip and there is a strong joint capsule but the ligaments are structured in a way that provide quite a lot of movement in this joint so some of the extra ligaments you have connecting the femur to the hip are the iliofemoral cubo femoral and Ischia femoral very straightforward names just saying there are ligaments between the ilium and femur pubic bone and femur and ischium and femur and one of the way these are structured is called the screw hole mechanism which means that when your hip is flexed like as you're bringing your knees to your chest you have a lot of movement in this joint booth when you're going for a run or something you don't really want your legs flopping around too wild so there are ligaments that tighten up on that joint depending on the flexion or extension in your hip it's pretty amazing stuff the knee joint like the elbow is uniaxial the articulating surface is a pretty poor fit there's not a nice socket but there are some adaptations to improve the stability in this joint for example there are menisci which are forming a deeper socket you know what I'm saying the bone of the tibia doesn't really cup around the femur much but the menisci do make a bigger cup for the femur to sit in to stabilize the joint to minimize the rocking of that joint and then these extra ligaments you've probably heard of at least some of them inside the capsule of this joint are intracapsular ligaments like the ACL and PCL on the outside our extra capsular ligaments call the LCL and MCL we'll look at those more in lab although you can see a picture of the lab model here when I say LCL and MCL that is the lateral collateral ligament and medial collateral ligament remember collateral is like if you're buying something and you need to have a little extra money on the side or in a military situation where there's extra damage besides the damage you intended to do that's collateral damage so they're extra on the side so the collateral ligaments are on the side of the joint the ACL and PCL are the anterior cruciate ligament and posterior cruciate ligament and the view of this model shows it from the back and you can see the posterior cruciate ligament is right in the center of the back of this joint the anterior cruciate ligament is kind of hidden from this view and from the front it's deep inside the joint but it's just below the patella within the joint I want to take one minute to look at video that gives us some idea of how the heck do you know what's going on inside a joint without cutting it open right like how does someone diagnose a tear in your ACL for example so we'll watch a 90 second video to see how that's done but I want to just quickly acknowledge here that there are many different types of joints that we have not talked about and you can use terminology in addition to all the stuff we've already learned like the valen would refer to things like the humerus at the pectoral girdle there are hinge joints and pivot joints and so on we won't study all these in detail but this is terminology that you may need to learn in the future so go back to this video we'll just finish with this this isn't something that you will be tested on it's just to give you an idea about again how these joints work inside our body and how maybe some of you interested in this field will one day be able to diagnose problems with articulations next test we're going to perform is to determine if there's an ACL tear the ACL ligament is designed to prevent translation into translation of the tibia and the femur so I'm going to position the patient at about 80 to 90 degrees of knee flexion from that position I'm going to literally sit the clinician will sit onto the foot of the patient to stabilize from there my hands my thumbs are going to come up into the joint line of the tibial plateau and I'm going to take up the slack with the back of the gastroc and get her to the bone and from that position I do a quick jolt or a quick into your translation from this position what I'm looking for is to see if there is a shift of the tibia plateau in an anterior displacement compared to the opposite leg from this position I'm as we'll show you the PCL test or posterior test excuse me posterior drawer and this is going to test the PCL from that same position I'm going to take up the slack and I'm going to give a jolt in a posterior direction onto tibia looking for any subluxation or movement takes place at tibia vs. femur