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
hyper extension or what you could think of is just going backwards.
It's going to be a painful one.
Let's do this.
You are looking at a right human knee.
So, I'm going to quickly orient you so you 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'd be going into the thigh and
then you're going to notice that there are two bones down here.
You have the tibia here which is that thicker more medial bone, meaning, again it's on the
inside of the knee and then you also have the fibula right here which I always tell
my students "fibulateral" 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 probe so 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 sesamoid bone is a bone that developed inside of a tendon.
So, if you looked back here, you're going to notice that there is a mass 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.
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Alright, let's get back to it.
Now, you may be wondering what's the difference between a tendon and a ligament.
Now, there are most simple definitions are going to be a tendon connects muscle, again,
which would be the quadricep muscles here in the thigh to bones.
So, tendons connect muscle to bone and ligaments connect two bones to one another 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 the tendon.
So, when the muscle contracts and pulls on all that collagen it's then going to 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 it like this - If I were to kind of bend this down, I don't
know if this is coming across that one 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 - say 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 inside of the knee and I'm going to try and point to it about right here.
A little difficult for me to see but 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 Cruciate because they cross.
They go like this.
Most of you would refer to them as the ACL and the PCL and again, they're defining the
range of motion.
So, if we go in here, the ACL, again, that ligament that you're seeing, 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 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 backside.
Um, 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 backside of the
knee.
So, now what I want to do is 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 an 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 can definitely see what we call Genu
Recurvatum and that's 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 genu 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 genu recurvatum as much as it's due to a missing and just again,
an absent meniscus but you can see what our 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 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 have - again, we should probably say like, how would - how bad is this hyperextension?
Are your toes coming up and touching 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 reducing
hyperextension, 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 popliteal but
not even just that, we have to talk about the meniscus.
So, the meniscus, let's 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 cartilage in this pad that actually
helps to distribute forces from the femur to the tibia.
So, 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 meniscus actually move with the joint during normal
range of motion.
So, if you all of a 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
going to 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 be far more subtle but that doesn't mean the damage isn't also
very intense.
Let's say you land and the tibia comes up let's say - this is going to be kind of hard
to demonstrate but let's say it comes up like this far, right?
It comes up that far, you could definitely start damaging that arcuate and the oblique
popliteal in the back.
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 the anterior to the
femur.
Well, how much damage is accumulating there, we judge that by what are called Grades.
Now, grade 1 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.
Think like rolling an ankle.
Grade 2, 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 2, picture like a partial tear in here but it doesn't go all the way through.
That's a much more serious injury.
You're you possibly may need surgery depending on how extensive it is.
You're going to need possibly rehab.
It's a much more extensive injury and then grade 3 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.
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 10degrees of hyperextension
which is essentially nothing.
So, anything beyond that, you are now starting to damage tissues and that's going to just
really affect your overall stability and you have to understand, depending on how severe
it is, you're also going to have scar tissue forming and scar tissue it contracts.
It locks areas down.
So, let's say 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 they don't just only happen - all
this whole process doesn't only happen to hyperextension.
I mean, if you get hit from the sides of the knee 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 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.
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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 at 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 Institute of 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.