the human knee takes a ton of abuse over the course of a day whether you are walking running or even just going up and down the stairs there are a ton of forces being placed on the joint which is why if those forces push the joint into a direction it's not supposed to go there can be some pretty intense consequences and that's why in today's video with the help of the cadavers here in the lab we're going to take a look at the knee joint and see what i personally believe to be the worst possible direction the knee can go into and that is hyperextension or what you can think of is just going backwards it's gonna be a painful one let's do this you are looking at a right human knee so i'm going to quickly orient you to understand what you're looking at this is the anterior aspect or the front of the knee and as i rotate it around this way this is the lateral aspect or the outside of the knee then this is the posterior aspect or the back side of the knee and then finally we have the medial aspect or the inside of the knee now you're also going to notice this massive bone up top this is the femur bone this is the largest and strongest bone and thickest bone in the entire human body so that makes this the superior aspect of the knee so we'll be going into the thigh and then you're going to notice that there are two bones down here you have the tibia here it's that thicker more medial bone meaning again it's on that inside of the knee and then you also have the fibula right here which i always tell my students fibo lateral to help you understand that it's on the lateral side because it's fibula now there's also another bone here which i'm going to smack with my probes you can hear it this is the patella or what most people would refer to as the kneecap now i can actually reflect this down and you can see that inner surface right here of the patella and that's going to be articulating with the femur there but the patella is what's called a sesamoid bone and a sesamoid bone is a bone that developed inside of a tendon so if you look back back here you're gonna notice that there is a massive amount of connective tissue here above the patella as well as below the patella well this used to be one continuous band and then the kneecap that patella developed inside of it and this just strengthens the overall integrity of the tendon itself but we can now also define this as being the quadriceps tendon meaning that the quadricep muscles are actually going to attach to the patella via this piece of connective tissue and then below it we can call this the patellar ligament and that's just going to connect the patella down to the tibia i want to take a quick moment and thank the sponsor of today's video keeps keeps is a subscription service devoted to helping men keep their hair they do this through clinically proven treatments with most customers starting to see results around six months or so after starting treatment these treatments are affordable and they're 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but it doesn't really tell you all that much about what their actual function is so tendons are there with muscles to generate movement at a joint so as the muscle contracts it pulls on the tendon which pulls on the bone which generates movement at a joint a ligament on the other hand defines the range of motion it says you can only go this far because tendons and ligaments are both made of dense amounts of collagen collagen is a structural protein that is really good at being or resisting being pulled apart so if you put a massive amount of collagen right here this is going to when this gets tight that's as far as it's going to be able to move the same goes with a tendon so when the muscle contracts and pulls on all that collagen it's then going gonna pull the joint like a rope so tendons again are there to help generate movement ligaments are there to help limit or prevent or define the movement that's available at that joint and i can show you some other ligaments here on this lateral side we have what's called the fibular collateral ligament also known as the lateral collateral ligament most of you would just call it the lcl and this is going to connect the fibula up here to the femur and this is going to define the range of motion for this side you can kind of picture if i like this if i were to kind of bend this down i don't know if this is coming across that well in the camera i'm obviously not going to do this too much because i don't want to break it but if you were to try and bend this that would put stress on this ligament here and it would say no you can't bend that way if we go to the opposite side you're going to see a more massive ligament here called the tibial collateral ligament or the medial collateral ligament again most of you would just say mcl and this is going to do the same thing it's going to prevent and define the range of motion so it's going to as i try to bend it this way it's going to get tight to the point where it won't let the knee bend in that direction but there's other ligaments that we're going to want to take a look at and as i reflect it back this way this might be a little difficult for you to see but i'm going to kind of scoot it forward now i can actually grab this femur here and i can rotate the knee and as we do that you can see the the inside of the knee and i'm going to try and point to it about right here a little difficult for me to see a bit about right there should be a ligament called the anterior cruciate ligament and then behind it is another ligament called the posterior cruciate ligament now they're called the cruciates because they cross they go like this most of you would refer to them as the acl and the pcl and again they are defining the range of motion so if we go in here the acl again that ligament that you're seeing it's it's like a cord right in there it's actually prevents the tibia this bone here from sliding forward in relation to the femur so if you can kind of picture that the whole lower leg going forward if it was able to do that that would mean that the acl has been compromised if not outright broken and then the pcl prevents the inverse it prevents the tibia from going posterior in relation to the femur so there's also going to be some ligaments on the back side you have the arcuate popliteal as well as the oblique popliteal ligament but these are going to be not nearly as strong but they're again there to reinforce the back side of the knee so now what i want to do is discuss well what happens when you hit the knee like this when you cause the entire knee again this is that anterior aspect to buckle to go backwards to hyperextend to go in the wrong direction now in all actuality not every form of hyperextension of the knee is going to be due to an injury in fact it happens naturally all the time you see this in adolescent girls interestingly enough although we don't fully understand the exact mechanism as to why that is and we also see it in individuals with connective tissue disorders they can have an extreme disorder or a very light disorder but if there's any excessive movement in the ligaments we call this hypermobility then you're you can definitely see what we call genu recurvatum and that's this this bending right this bending backwards of the knee now the reason why that can be a problem if we come back to this knee here if i reflect this back again and we look at the articular surfaces of the femur and the tibia below it right the joint surfaces they have aspects of their surfaces that are meant to articulate or touch one another if you had geniu recurvatum and you're and i can't even do it i mean the cadaver knee still won't let me do this and you're bending more backward different aspects of the joint surfaces would be touching one another than is what than what's meant to be and that can actually create arthritis and interestingly enough this cadaver had some arthritis right here this though isn't due to geno recurve bottom as much as it's due to a missing and just again an absent meniscus but you can see what arthritis would do and that's going to create a lot of pain and reduce range of motion in the joint but when it comes to injuries on the other hand injuries i really shouldn't say that it always is going to be high impact or or rather i mean it can be high impact but impact hitting the front a lot of the time it's actually just due to landing inappropriately let's say you land like this well that can obviously cause the tibia to move forward and that would compromise that acl on the inside it would compromise those ligaments on the back that we discuss like the arcuate popliteal and the oblique popliteal because those are all preventing hyperextension and if it's excessive enough it can even get to the pcl which the pcl is really going to be hard to see but it is behind that acl there if you had again we should probably say like how how bad is this hyper extension are your toes coming up and touching your nose if that's the case that's catastrophic that's so catastrophic i mean the sheer amount of destruction you would likely also blow out aspects if not all of the mcl the lcl because even though they're not the biggest contributors to uh reducing hyperextension they deal they do contribute to that you're going to blow out the acl the pcl you're also going to blow out again that oblique popliteal the arcuate arcuatepopliteal but not even just that we have to talk about the meniscus so the meniscus you'll see if you can see this i'm going to touch it with my finger first it's hard for me to see this here there's this soft surface here that is called a meniscus that's the lateral meniscus and what it does is it's a cartilaginous pad that actually helps to distribute forces from the fever the femur to the tibia so if if that's gone then what happens is you get bone on bone contact like we have here and then arthritis can form but these menisci actually move with the joint during normal range of motion so if you all the sudden just have this excessive hyperextension well what that can do is it could even start tearing meniscus so and then at the same time i mean your skin could possibly rupture i mean picture the skin rupturing here all the muscles that are also in this area you're gonna be rupturing them toes to nose is so catastrophic i mean i wouldn't be surprised if amputation would be required most of the time it's going to be far more subtle but that doesn't mean the damage isn't also very intense let's say you land and then and the tibia comes up let's say this is gonna be kind of hard to demonstrate but let's say it comes up like this far right if it comes up that far you could definitely start damaging that arcuate and the oblique popliteal in the back um you can definitely start damaging the acl for sure because again the acl is trying to prevent its whole purpose is to prevent the tibia from sliding anterior to the femur well how much damage is accumulating there we judge that by what are called grades now grade one just means there's going to be some small tears maybe but there's a little bit of inflammation there's some pain but typically people heal pretty well from this thing like rolling an ankle grade two that is where you get a partial tear so if we come back here again so think like grade one tiny little tears this is the patellar ligament tiny little tears but you're able to scar those over heal it it's not typically the end of the world grade two picture like a partial tear in here but it doesn't go all the way through that's a much more serious injury your you possibly may need surgery depending on how extensive it is you're gonna need possibly rehab it's a much more extensive injury and then grade three is a full on rupture where the segments are no longer continuous with one another you're definitely going to require surgical repair or you may even require transplantation some of you probably heard of people getting an acl transplant and so what they actually can do is take an acl from a cadaver like this well not one that's been embalmed because that would be madness but they could take an acl from a cadaver and then actually transplant it into you or they can actually take connective tissue from a different part of your own body and place it in there to make a new acl so it really just depends on how severe of the hyperextension was and how much damage it causes and but regardless even a small amount of hyperextension can have some pretty intense consequences because the knee as they say should only really do about at most 10 degrees of hyperextension which is essentially nothing so anything beyond that you are now starting to damage tissues and that's gonna just really affect your overall stability and you have to understand depending on how severe it is you're also gonna have scar tissue forming and scar tissue it contracts it locks areas down so let's say you you blew out the arcuate and oblique popliteal ligaments and if you have scar tissue forming in this area that can restrict movement even more to the point where sure even if you had it repaired or even if you did rehab if you didn't if you have too much scar tissue it can now reduce the range of motion so look knee injuries are always going to be bad and there don't just only happen this all this whole process doesn't only happen to hyperextension i mean if you get hit from the sides of the knee that all this can still happen to the lcl to the mcl it just goes to show that you know joint issues are extremely problematic and you can see why they can affect people for years and years and years and and essentially never go away thanks for watching everybody i really hope you enjoyed today's video again i want to say thanks to the sponsor of today's video keeps you can find a link in the description below as always be sure to like comment subscribe those types of things really do help the channel perform better so we can get in front of more people and teach them more anatomy and until next time just be sure to take care of those knees you only get two of them so once they're gone they're gone but if that does happen you know i guess you'll have more time to watch more instituted human anatomy videos so i guess it's not all that bad but still regardless take care of those knees and i will see you next time [Music] [Music] you