why do you have a kneecap i'm sure that's a question you ask yourself every single day because you're so concerned about learning more about your own anatomy now many people will say that the kneecaps function is to help protect the knee joint and although they're not totally wrong it's definitely not the only let alone the coolest function of the kneecap so in today's video we're going to talk about this cool mysterious function of the kneecap and a little bit of a hint it has to do with the quad muscles that many of you love to work out during legs day so we'll take a look at a real human cadaver with our knee dissection look at the quads and that'll help us answer this mysterious question so let's do this so let's start with what is the kneecap well the kneecap is truly referred to as the patella patella translates to little dish or small dish and this is a bone on the anterior surface or the front of the knee so we have a cool cadaver dissection that we'll look at here's the right knee and the anterior aspect or the front surface here is the kneecap embedded in this tendon that we'll refer to in a minute here and you can see the quadricep muscles up here now i did steal cornelius's right kneecap the skeleton just so you could see how it would look if we dissected it out of the tendon here and kind of superimpose it there this pointy portion that faces inferiorly or points downward is called the apex the top portion is referred to as the base now many people will say well the kneecap it's job it's on the front of the knee so it's probably going to protect the knee but let's take a look at this when i reflected away now besides being totally awesome to actually see the cartilage on the femur and the posterior articular surface of the patella and whenever you hear about an articular surface in anatomy it typically is going to refer to a joint and these surfaces tend to have cartilage on it fyi for this one this is arthritic as you can see the cartilage isn't smooth and glossy like it should be it gets a little bit more smooth and glossy down on the femur where it articulates and this surface here of the patella should articulate in this groove of the femur because we love names in anatomy and that groove is referred to as the intercondylar groove because there's two condyles on the either side of the femur and inter just means between now after all that name dropping just again look at where the patella is sitting in an extended position or when the leg is straight so i reflect that down it's not even over the internal joint anatomy of the knee when you're in an extended position so in a way you're like okay well do i need it to protect another bone called the femur not really now granted the patella will slide and glide based upon position in an extended position the patella tends to be upward but when you bend your knee or flex your knee the patella tends to slide downward in relation to the femur here so it kind of slides and glides in relation to the femur when you bend tends to go downward when you straighten tends to go upward so you could maybe argue well in a bent position i might have some more coverage over that joint anatomy which would be great for crawling when you're a little toddler you know learn before you learn how to walk but there's a problem with that your kneecap doesn't even fully form or start to really ossify or become bony until the ages of two to six which at that point most of us have been starting to run around and jump around like crazy little toddlers and so in that case we're not getting all this protection from a hard bony kneecap when a little baby is actually learning to crawl so again it's kind of coming from this ideas it's not really totally all about protection here granted when it is covering that in a flexed position you could say yeah that could provide a little shield there but that's not its main function so if protection isn't its main or only function what is it there for well you see the patella is a specific type of bone referred to as a sesamoid bone sesamoid bones are bones that develop inside of tendons and you can definitely see on the cadaver dissection that the patella is engulfed in this tendonous structure now these tendons where the sesamoid bones develop in often undergo high amounts of friction compression and other stresses and sesamoid bones can actually vary from person to person in number now some common areas that you'll find them are at the base of the thumb so if you were to take an x-ray you could see these little sesamoid bones often at the base of the thumb this joint is technically called for you anatomy geeks the metacarpal phalangeal joint you often also see them in kind of the equivalent joint of the foot like the big toe that the big toe joint is called the metatarsal phalangeal joint and you'll often see some small sesamoid bones there and most of the time these sesamoid bones are a few millimeters to a few centimeters in size except for the patella which by far is the largest sesamoid bone and it's the most consistent every person typically has a patella unless there's some abnormality that's uncommon so you're probably thinking well great jonathan you told us what a sesamoid bone is but what does it actually do well remember those sesamoid bones tend to form in tendons that undergo high amounts of friction compression and other stresses so one of the jobs is to help protect that tendon from excessive wear and tear and another one is to help improve the mechanical advantage of that tendon specifically the muscle that's pulling on that tendon or in other words increase its leverage so the muscle becomes more powerful and that's exactly what happens with the quadriceps and the patella so let's take a look so we're going to take a look at a slightly different angle of the quadriceps and the patella again here are the quads that you can see here but then from this view you can see that protrusion of the patella now the quads are called the quadriceps muscles because it's a combination of four different muscles on the outside you can see this muscle which is called the vastus lateralis because it's vast and large and on the outside and then we've got the vastus medialis here because it's vast or large and on the inside and then we've got the rectus femoris rectus just means straight up and down over the top of the femur if i reflect that out of the way there's a muscle here called the vastus intermedius because again large but in between the vastus lateralis and medialis here now if you don't care for the names i know we have some of the anatomy geeks who love muscle names but the key point is that these four quadricep muscles will converge into a common tendon here called the quadriceps tendon and that tendonous band will continue down onto the front of the shin bone on that bump you probably felt it underneath your kneecap this bump is called the tibial tuberosity and that's where the tendonis band actually attaches to bone and can exert its force so when we're talking about exerting forces that's when the muscle will actually contract and the net direction of pull of the quadriceps is upward so when these muscles contract and pull they pull on this tendon and this tendinous band and therefore because it's attached to the bone has to pull on the bone and when the quadriceps contract we say they straighten the leg or extend the knee so like when you're kicking a ball or standing up from a squatting position now one quick thing that i just need to mention because anatomists love naming thing yes this is a continuous band of tendonous tissue here but technically from here to here they refer to this specifically as the quadriceps tendon and below the patella down to the tibia they call that the patellar ligament ligament because technically ligaments connect bone to bone even though we know that it is one continuous band and the patella formed afterwards so when we're talking about the contraction of the quadriceps muscles and the relationship of the patella looking at it from this angle you can see how the patella protrudes upward and that quadricep tendons i'm going to kind of exaggerate has to kind of bump up and then go down so it's kind of like this up and down onto the actual tibial tuberosity there and that creates a huge amount of leverage for the quadriceps tendon and therefore the quads and because of the leverage that that bump creates with the patella you can get strength increases i shouldn't say you get strength increases because you're born with the patella well the patella develops after you're two to six years old but because of the presence of the patella the quadriceps are 30 percent stronger than they would be without it now i have a whiteboard session to drive this point home a little bit further and i think it'll help make a little bit more sense so to the whiteboard welcome to the whiteboard everyone you can see we've got our diagram here this is representing the femur the tibia and then the patella or our kneecap here and we're looking at it from a slightly bent deep position like you could see here from an inside or a medial view now the whole point of this diagram is to help show the mechanical advantage or the leverage that the patella helps create for the quadriceps muscles now the quadriceps are represented by this red line coming up in the direction of pull which we knew the quadriceps pulled upward exhibiting that force upward and will eventually move the tibia into an extended position or the knee into an extended position this green is representing a moment arm or what we call a lever arm here and you can see i put two different distances here the one that's naturally occurring in our body with the patella versus what it would be like without the patella and because this lever arm is increased the distance from the the angle or the axis point where we actually do the swiveling from in our joint that provides more leverage think of it from a perspective of say like if you've ever been turning a wrench to loosen a nut or a bolt the longer the handle of that wrench and the further out you grip makes it so much easier to loosen stubborn bolts that you're working on on like household projects that's kind of the same concept that's happening here you're turning this wrench with your quads and the further the distance you have the more leverage it creates for your quadriceps and like i said some studies say the benefit is up to 30 of strength increase because we have the patella versus if we didn't have the patella we lose length on that lever arm and not have as much force because of that decrease in leverage so that's a really crazy thing to think about that our body incorporates this type of thing but i do want to mention one last thing as we swivel like so flexion and extension of the knee the patella will slide and glide and it will change its mechanical advantage based upon the joint angle most studies say that the most mechanical advantage or most leverage is exhibited in the range of motion about 20 to 60 degrees just to give you an idea this is about 90 degrees of knee flexion so the most mechanical advantages about from here to here in that 20 to 60 degree range i may have gone a little further though so only to the perfect degrees there but 20 to 60 degrees and you still will get mechanical advantages throughout the whole range of motion but like i said that 20 to 60 degree degree range is where you get the full full benefit here so think about how anatomically awesome you are you have these simple machines or these pulley systems in your own human body so i think you should be excited about that if you're interested in going into the medical field and more fully understanding the human body you're gonna have to learn a little bit more than just anatomy and physiology like in today's video understanding the biomechanics of the human body requires knowledge in physics and math and that's why i want to say thank you to today's sponsor brilliant brilliant is an online interactive learning platform for stem subjects that is math logic science and computer science brilliant helps you develop not only just knowledge but also problem solving skills so that you can think more creatively ask the right questions and apply that knowledge to real world situations and that's one of the most important things you can do is applying knowledge that you learned to what you're actually doing in life brilliant has also just released a new interactive course called scientific thinking this will help you explore principles in engineering as well as physics and of course apply those lessons to how the world works around you including how the human body works and utilizes those principles in its own design and function i personally like the lesson on pulleys and lifting elephants in the air because you know then i can apply those pulleys to 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