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Transcript
00:00Your knees, you're going to miss these when they're gone. These are the biggest joints
00:18in the body, I think. The reason they're so big is because they take your entire body
00:23weight, which means that you take them for granted because you're using them all the
00:26time when you're getting around. If you start to develop problems with your knees, you're
00:30going to have problems getting around. And believe me, it is going to cause you some
00:34big issues. So that's what we're going to talk about today. As I've got to try and think
00:40of things to talk about for the rest of my career on YouTube, we're going to limit it
00:44today. Also, otherwise, if I go into detail about things, I'll be here for hours, won't
00:49I? So we're going to do the bones and the ligaments of the knee joint. Maybe a little
00:54bit how it moves, that sort of thing, right? So we're talking cruciate ligaments.
00:57How is everybody today? Is everybody okay? I don't know why you're here. I mean, I just
01:10started making these videos two years ago, making these little videos just to keep myself
01:15interested. Now, we've had a million views and we've got 20,000 of you guys subscribed.
01:21I don't understand. Anyway, if it's useful, I am surprised and pleased, I guess. Right,
01:30the knee. The knee is a hinge joint. It tends to just move like this. So we have extension.
01:39God, this one doesn't extend very well. We have extension and flexion and extension and
01:49flexion. But hopefully, it doesn't really move side to side very much and the bones
01:56stay where they are relative to one another. So it's a synovial joint, which means it's
02:00quite a complicated joint and there's plenty to talk about. In my life, before I started
02:04talking to people about anatomy, this was my research area. I used to study articular
02:10cartilage biology. I was just getting going really when I ended up doing this teaching
02:15job. Hey, talking about anatomy is fun as well, so whatever. So these articular surfaces
02:21are covered by articular cartilage and this is particularly important in big joints like
02:26the knee and the hip because of diseases like osteoarthritis. Now, there's a bit of a misnomer
02:33that you can wear your cartilage out and it's a wear and tear thing, osteoarthritis. It's
02:39not really true. I mean, if you change the biomechanics of the joint, if you make the
02:43joint so it's not as strong as it normally would be and you get more pressure on one
02:46side than the other, then yes, you're overloading the cartilage. You can start to cause some
02:51pathological changes. But generally, if, for example, you're a runner like me and you're
02:56nice and straight and you've got strong knees and everything's balanced, running, that loading
03:01will make your cartilage thicker, happier, healthier cartilage, just like all the other
03:05tissues in the body. If you load it, it gets stronger. So we have a synovial joint like
03:12we do in any joint in the body, any joint in the body, that allows a wide range of movement.
03:18So when we look at the bones, we see this nice smooth covering and of course the articular
03:21cartilage is missing here but that's what would be there, particularly if we look at
03:25any real bones. Okay, so what about the bones then? So if we consider the femur, we're not
03:31interested in this end today, we're interested in this end. We've probably talked about this
03:34end when we talked about the hip joint, didn't we? We're just going to look at the distal
03:38end of the femur, these bits down here. So what we find is that the diaphysis flares.
03:45Let's get the patella out of the way. And then we see this shape. Now these are the
03:51two condyles. That's medial, that's lateral. So that means that this is the lateral condyle
04:02and this is the medial condyle. They get called condyles. Condyle comes from the old Greek
04:07word for knuckle. And they do, they look like knuckles, don't they? And the bits of
04:10bone either side here get called the epicondyles because they're upon the condyles. But that's
04:16the bit we're really interested in. These two condyles, big articular surfaces that
04:21then are going to articulate with the tibia. And we can see that the articular surface
04:27extends up here and creates a little groove that the patella is going to run into. More
04:34about the patella later. So in between the two condyles we have this kind of intercondylar
04:41bit here. And this is where we're going to see some of our ligaments running. But that's
04:46about it. Two condyles, an intercondylar bit and what have you. Now if we look at the tibia,
04:51this is the proximal end of the tibia. You can see it's got kind of this flattish platform
04:57which is why it gets called a tibial plateau. And these again are the lateral and medial
05:03condyles of the tibia. Straightforward, right? This here is the tibial tuberosity that we'll
05:10find the quadriceps muscles inserting into. But we're not really going to talk about the
05:15muscles. We must have done the hamstrings and the quadriceps, right? We must have done
05:20movements of the knee joint. And can you see how there is a bit of a sliding motion and
05:29there's a rolling motion. But for the knee to work, the two bones kind of need to stay
05:34in place and almost spin over one another. So the condyles kind of spin over the top
05:41of the tibia. And you can see the articular surface is nice and big and rounded because
05:48as it flexes we keep articular cartilage in contact with articular cartilage. We can do
05:54a whole other video about the synovial joint itself and blood supply and nervous things
05:59and that sort of thing. Alright, patella. The patella is a sesamoid bone. So a sesamoid
06:06bone is, it's a bone within a tendon usually. So normally we find, sorry, doesn't move like
06:18a normal person does. Because he's bolted together, not got all the other bits we have.
06:23Most bones are attached to other bones. Most bones are next to other bones and articulate
06:27with other bones. A sesamoid bone is kind of a floating bone. And this sesamoid bone,
06:32the patella, is inside the tendon of the quadriceps. The quadriceps comes and crosses the knee
06:38joint and inserts into the tibia at that tibial tuberosity that we saw. And when we contract
06:47quadriceps femoris, we extend the knee joint. We straighten all this out, right? The patella
06:53gives a bit of a mechanical advances there and what have you. Now what that means for
06:58you terminologically is, this chunk, rope, of connective tissue is running from the patella
07:10to the tibia. So it gets called the patella ligament. But as far as I know, and I'm pretty
07:17sure about this, because we used to do tendon stuff and ligament stuff. See, tendons, tendons,
07:23they're quite well, they're reasonably well understood histologically and functionally
07:27and what have you. Because athletes and people keep damaging tendons and you have to work
07:32out how to repair them and that. You know, there's a bit of a business there. Ligaments,
07:35the biology of ligaments, as I understand it, is still really poorly understood. People
07:40haven't really looked at it in the same way they've looked at tendons. So, in your anatomy
07:45textbook it'll tell you that the ligament runs from bone to bone. So this gets called
07:50the patella ligament. But really, it's a tendon. It's got tendon stuff in it. It acts as a
07:57tendon because it's actually this muscle coming together as a tendon around the patella and
08:02inserting in here. So really, you should think of it as a patella tendon. You know, if you're
08:06thinking about Golgi tendon organs and that sort of thing, detecting the stretch of a
08:10muscle, that sort of thing's in here. Not the sort of stuff you get in ligaments. Patella
08:14tendon. People may call it patella ligament. They're not necessarily wrong. You should
08:19think of it as a tendon, right? So the patella then slides up and down in that groove. Why
08:24am I talking about the patella? I can't remember. The patella's also got articular cartilage
08:29on the back of it. We're not really talking about the patella today. I guess I'm just
08:33on my high horse talking about... Right. Back to the matter in hand. It's just because we
08:42were talking about the bones, isn't it? You've got the two bones. Might as well talk about
08:45that bone as well. But whoop, there we go. So, flexion extension. So we've got the femur
08:52articulating with the tibia and we've got these pads in here as well. And these are
08:58the menisci. We have a lateral meniscus and a medial meniscus. And what they're doing
09:06is... You can't see it too badly on here, but they're filling in the space around the
09:13articulating bit. They're adding support to the articulating surfaces, right? So it can
09:21move around a bit. There's a bunch of ligaments holding them in place and that sort of thing.
09:26Often if someone says, I've had my cartilage removed from my knee, as a cartilage biologist,
09:33I think, what? You've had your cartilage removed? That's... What they actually mean
09:38is they've had the meniscus removed. So people can tear the meniscus and that sort of thing.
09:43Sometimes the easiest thing to do is just take it away and it stops causing pain and
09:47what have you. Because like other structures around here, they often don't repair very
09:51well when they start to break down. Lateral meniscus, medial meniscus. I think they're
09:59kind of like almost rings, C shapes, almost rings, a little bit variable in people. But
10:07in the middle then, the articular surfaces of the condyles of the tibia and femur are
10:12touching and rolling against one another. But the meniscus is kind of supporting the
10:20bit around the outside, right? And keeping it in place. So the menisci are kind of space
10:24fillers. They're thicker laterally, thinner medially. So it's kind of a ring wedge thing,
10:31if you can get a ring wedge shape inside your mind, if you can imagine that sort of thing.
10:36So they're important functionally and even though you can have them removed, they're
10:39important functionally, honest. Okay, so what about the ligaments then? Let's do the easiest
10:44ones first. So here's the fibula. Now, we didn't really talk about the fibula because
10:51the fibula isn't really involved in the knee. It's very much the tibia and the femur that
10:57are the knee joint. But the fibula is lateral, it's on the outside of the leg. And you can
11:03see a ligament here and a ligament here. These are the collateral ligaments and they give
11:09the knee stability. They stop the knee from bending that way or that way, in a valgus
11:15or varus direction. So they keep the knee as a hinge joint, not as a side to side joint.
11:20They stop it being a side to side joint, right? So this can be, this gets called the
11:26lateral collateral ligament and this gets called the medial collateral ligament, which
11:33is nice, right? They also get called, because this one goes from the femur to the tibia,
11:38this also gets called the tibial collateral ligament medially. And this one, because it
11:44goes to the fibula, so this is where the fibula gets involved in the knee joint, this ligament
11:49also gets called the fibula collateral ligament. So if, these can be damaged, so if someone,
11:59if there's a blow to the knee from this side or from this side, so you forcibly bend the
12:04knee joint in that direction. And these bones are long, so you've got big long levers on
12:10this joint, which means you can put a huge amount of force through it in an inappropriate
12:14way which can damage these ligaments. So if you do that, the ligament can stretch or
12:20rupture and then you'll get some laxity in this, in this way, right? Either that way
12:25or that way, depending upon which one has been damaged. Does that make sense? If you
12:28can imagine this one's been torn, then this will give you more movement that way and vice
12:33versa. Okay, so now those are the superficial ligaments, let's go and have a look at the
12:38deep ones in here. And these are the cruciate ligaments. The cruciate ligaments, there's
12:44two of them, they get called the cruciate ligaments because they cross over one another.
12:49So there's a, there's like a cross there. And there's an anterior cruciate ligament
12:54and a posterior cruciate ligament. Now how do you remember which is which? Because they
12:59both run from anterior to posterior, posterior to anterior. Now remember that, that space
13:05we talked about in here? Alright, so that, that's that intertrochanteric space in there.
13:13So we've got this, this groove and this ridge in the tibia there, but it's inside that space,
13:20inside that gap, that's where the cruciate ligaments run. So the job of the anterior
13:27and posterior cruciate ligaments is to hold these two bones together. But not just together,
13:35but while they're moving. So when you flex your knee joint, you have a little, we have
13:43a bit of rolling of the femur, but you kind of want to convert that into a, into a spin
13:48motion so that the femur, this articular surface is, these condyles are spinning on top of
13:55the tibial plateau, right? So the two cruciate ligaments that cross between the tibia and
14:04the femur like this, as they, they allow this to happen, and we've actually got these
14:10built into this model which show how this happens, and they do, they do, their laxity
14:15does change a little bit through flexion, but essentially they're holding the two bones
14:20together while they spin like this. Now the anterior cruciate ligament, the anterior cruciate
14:30ligament gets called the anterior cruciate ligament because here it is here. So it starts
14:35off from this anterior intercondylar area here, and runs through that gap to attach
14:44to the lateral condyle of the femur, do you see? So it's going from the anterior intercondylar
14:53space here on the tibia, and then it's running posteriorly and inserting into the, the lateral
15:01condyle of the femur. So if I turn this knee around and we look at it posteriorly, that's
15:05it there. So look, there's the, there's the fibula, so this is lateral, right? So that's
15:15it popping out there, this is the posterior knee, the popliteal region, that's the anterior
15:20cruciate ligament popping out posteriorly there, okay? So that means that this other
15:26ligament here, in fact we've got a couple, this ligament here is the posterior cruciate
15:30ligament. Now the posterior cruciate ligament is for the posterior, it's staying posteriorly,
15:35look, it's running from the posterior part of that intercondylar groove towards the,
15:40this is the medial side, look there's, there's fibula, so this is medial, we're looking at
15:44the posterior knee, and the posterior ligament runs to the medial condyle of the femur, okay?
15:53So the anterior cruciate ligament runs from the anterior intercondylar groove, it runs
15:59posteriorly through that gap to insert into the lateral condyle of the femur, whereas
16:05the posterior cruciate ligament runs from the posterior part of this intercondylar
16:10groove to the medial condyle of the femur, so from tibia to femur like that. And those
16:15two then, as the joint flexes and extends, it holds those two in place. Now, the anterior
16:24cruciate ligament is weaker, and if you rupture the anterior cruciate ligament, the other
16:28job it has is it holds, it stops the tibia from slipping anteriorly. So if the anterior
16:35cruciate ligament is ruptured, then you can, in a partially flexed position, you can pull
16:41the tibia anteriorly away from the joint, and that tells you the ACL, the anterior cruciate
16:46ligament is damaged. The posterior cruciate ligament then kind of does the opposite, it
16:50stops the tibia from slipping posteriorly, which you could also interpret as the femur
16:56slipping anteriorly over the tibia. Do you see what I mean? So the posterior cruciate
17:00ligament stops the tibia from displacing posteriorly, which is the same thing as the femur displacing
17:07anteriorly over the tibia, if you were to describe it in the other direction, right?
17:13So those are the anterior and posterior cruciate ligaments, those are really important. The
17:16other ligaments we can see in here then are ligaments that are anchoring the menisci in
17:21place. And I say anchoring, they can move a little bit, but we have a whole bunch of
17:25meniscus-whatever ligaments, and in most models you can only see one or two. But you see how
17:31this is attached to the meniscus? So they're kind of holding the menisci in place, and
17:34they are actually somewhat variable. So there are quite a lot labelled on this model, oh
17:41no, they're not, get in there! If you find them, if you want to study them, they get
17:46called meniscofemoral, meniscotibial, and there's a transverse meniscus ligament. So
17:51meniscofemoral ligaments, meniscotibial ligaments. Yeah, the clue's in the name, right, as to
17:57where they run from. But really, the guys you want to be totally nailed on about are
18:04the collateral ligaments and the cruciate ligaments. Absolute must-know stuff if you
18:12have anything to do with the knee. The other little trick that we should talk about is
18:17that although we say that the knee is a hinge joint, and it hinges, a little bit of rotation
18:26is normal. So when you extend the knee, for example, when you're standing on it like
18:31I am, the femur rotates medially, just a little bit. And so it extends and rotates, and that
18:40little rotation just means that it kind of gets a little bit better anchored on the tibial
18:46plateau, and you make a bit more of a stable column. So it's a little bit more energy efficient,
18:53I guess. It makes standing a little bit easier. But it means that when you go from an extended
18:58knee to a flexed knee, it has to unlock. So it just has to rotate back again, and that's
19:02Popliteus' job, I think. And then it flexes. There is a little tiny bit, we're talking
19:07like 5-10 degrees of rotation at the knee joint on full extension, and that's normal.
19:14What's not normal is when you put a lot of rotation through the knee joint, and that's
19:22one way of damaging the cruciate ligaments, and particularly the anterior cruciate ligament.
19:26And of course the way this happens is that the foot is planted in the ground, if you're
19:30playing rugby or football and you've got studs on, your foot is anchored to the ground, the
19:34body twists around that, it's the knee that ends up twisting, pop, goes the anterior cruciate
19:39ligament, and then you're in a world of trouble, and your knee will probably never quite be
19:45the same again. And that's unfortunate. Don't go thinking, oh, but we can do prosthetic
19:53knees and that sort of thing. It's not that good, it's not that easy. And of course if
19:58you have a damage to the ligaments of the knee, that throws back to what we were talking
20:01about earlier, and biomechanical instabilities and what have you, which are then somewhat
20:07more likely to cause degeneration of the cartilage and osteoarthritis in older age,
20:12but at an earlier age and things like that. So really, do take care of your knees, they're
20:16ever so good, and ever so important, and we take them for granted. See look, I've got
20:21this, I mean this femur is a really long lever, just imagine how much load you could put through
20:28that. The tibia is similar, right, so you can really twist and do horrible things to
20:33this poor knee joint. And the knee joint might be held together by these ligaments,
20:42but the muscles are also helping. The muscles always help joints as well. So if you've got
20:47strong quadriceps, strong hamstrings, and what have you muscles here, of course if you've got
20:52strong hip joints and strong ankle, that helps as well, that helps your whole stability and
20:56lower limb thing. But if the muscles across the joint are also strong, that helps the
21:01stability of the knee joint. And not just strong, but well balanced. So runner's knee,
21:09being a runner, you tend to get, if you do a lot of running, you tend to develop a bit of lateral
21:17knee pain. You think, oh no, my knee is bad, my knee's hurt, I need to rest. You don't need to
21:22rest. What's happened is that the, sorry I'm swapping to a leg from the other side, this is
21:32the lateral side here. What's happened is your iliotibial band has got tight because muscles
21:38are pulling on it, and that tightness is there, look, it's pulling on the knee joint, and it's
21:43just pulling on it in such a way that the biomechanics of the knee joint are disrupted.
21:47And instead of being nice and square, it's a little bit eee, eee, eee, eee, eee, eee, eee,
21:55and you get knee pain. Stretch it out, knee is good. See, with a lot of early biomechanical
22:04knee pain, a lot of sports-related knee pain, if you have a good stretch, if you've got quadriceps
22:08in your hamstrings, a lot of that pain will go away. Right, where were we? But take them out,
22:14exercise them regularly, make the muscles nice and strong, and they'll be good,
22:17all right? So a little bit of rotation is normal, a lot of rotation is catastrophic.
22:23We've covered the main bones of the knee joint, which are quite straightforward, right? Just the
22:28condyles, that groove in the middle, keep it simple. We've covered the major ligaments,
22:33the collateral and cruciate ligaments of the knee joint, and we've talked about how it spins with a
22:37little bit of rotation, how pretty much everything else is catastrophic. If you are in the gym
22:42lifting weights, do keep your knees nice and straight. If you're not sure whether you're
22:46doing a good job, get somebody to spot you, you know, get one of the instructors just to
22:51check your form. See, that's a lot of what I'm doing in the gym this time of year, just go back
22:55to basics, get my form good with low weights, and then start building the weights again,
23:00to keep myself safe, to keep myself strong, but also to keep my joints safe. I mean,
23:05there's nothing worse, is there, than going to the gym to make yourself healthy, and then
23:09injuring yourself. That feels a bit self-defeating, so do keep your knees, keep your knees safe,
23:16keep them hinging, not twisting, and if your knees are kind of twisting in and that sort of thing,
23:20that means other muscles aren't strong enough, alright? Okay, that's it, right, see you guys
23:28next week. Stay healthy, stay strong, look after your musculoskeletal bits.