As we move more inferiorly in terms of our discussion of the joints we get to the most
superficial as well as the most complex of the joint synovial joints of the body
and that's the knee if you think about where individuals have pain or troubles in terms of
their joints that knee often comes up as one of the more frequently damaged areas so let's
talk about what the knee joint actually is and it's really a combo similar to what we had in
terms of the elbow of three different joints now you're going to have the two femorotibial
articulations you will have the medial excuse me this is the lateral and this is the medial where
you have the condyles articulating the femoral condyles articulating with the tibial condyles
as well as the articulation between the patella and a femur so right here you can see that the
patella has been reflected off so you can see the inside of the knee joint but all of these
these three different joints are going to be within one articular capsule now what type of
joint is this we call this a complex or modified hinge joint so think about from what we discussed
before what actions can occur at a hinge joint that's right only flexion and extension can
occur here so let's talk about flexion and extension in the knee joint because it's slightly different than
other joints in the body all right so you can see here in terms of the model flexion is actually
occurring in a posterior direction where extension still is return to anatomical position so that's
a key point that I want to make sure that you understand when we're talking flexion in terms
of the knee joint that leg is moving posteriorly so important difference between other areas
of the body now one other thing that I want to note when we talk about a modified hinge joint
that means that it can slightly move in other directions in this particular case there
is slight medial and lateral rotation so when you're standing upright if you think about it when
you're standing upright say if you're teaching in front of a class for a couple of hours your
muscles could get really fatigued so you want to be able to relax those muscles but still be able
to stand upright so when you're fully extended your knee will slightly medially rotate in order
to kind of lock the knee into position and allow for those muscles to relax just a little bit so
in particularly those quadricep muscles so there is a little bit of medial rotation now when you
want to be able to flex the knee say if you want to start walking away from something what will
happen is your popliteus muscle will contract that will allow for lateral rotation of the knee joint
and remember these are all very slight movement so very slight lateral rotation to allow for flexion
of the knee joint to occur okay so that's what we mean in terms of a modified hinge joint all
right so before we get into the ligaments I want to talk about the importance of the muscles and
the muscle tendons in this region so in terms if you think about in terms of the the fit of the
bones the tibial condyles are extremely shallow so really those tendons and ligaments are playing the
main role in terms of stability now in terms of what's playing the biggest role that's going to
be tendons specifically your quadriceps femoris tendon okay so let's write that down and make
sure we remember this so quadriceps femoris so that complex of four big muscles on the
anterior portion of your thigh if you have well conditioned quadricep femoris muscle and tendon
that can offset any type of damage that you have in many of these ligaments we're talking about
here so that's what a lot of the conditioning goes into those particular muscles but I don't want to
give you the impression that these ligaments don't play a big role too they are also going to be
very important now this first one you know this is the patellar ligament and it's actually it's
referred to as the patellar ligament but that's really a misnomer it's really a continuation of
the quadriceps femoris tendon okay so it's from the point where as we recall the patella is
that sesamoid bone so the patella is a sesamoid bone meaning that it forms within the quadriceps
femoris tendon all right so the part of the tendon that continues from the patella down to the tibial
tuberosity of the tibia that's referred to as the patellar ligament all right it's a distal part of
that quadriceps tendon also as you can note in these pictures here you're gonna have
a fibular collateral ligament and a lot of times particularly clinically you hear this referred
to as the lateral collateral ligament all right but we know that's gonna be lateral because the
the fibula is always lateral so you can see that here a fairly rope like extracapsular ligament
and then on the opposite side you have the tibial collateral ligament alright so from the femur to
the tibia this one is significantly weaker than the fibular collateral ligament and anytime you
have a weaker ligament that often there's more often injured also very important to note is
that the TCL is attached to the medial meniscus and we'll talk about the medial meniscus more
in just a moment but you can see that right here so there's a connection so oftentimes if the TCL
is damaged the medial meniscus will be as well so recall in terms of our conversation of what
a meniscus is this is going to be composed of fibrocartilage all right so anytime you have
cartilage you know we're talking avascular so without a blood supply that means that there's
damage to this particular area it's very hard for this to heal as compared to other areas
of the body so your medial meniscus you can see here attached to your TCL and
then the stronger and more circular lateral meniscus now the lateral meniscus has a
bit more mobility so it's much less likely to be damaged than the medial meniscus so
if we recall this is a perfect place to have a meniscus because it's sitting within these very
very shallow tibial condyles so allowing for a better fit for these large femoral condyles
all right so continuing on so we're talking now intra-articular so within the articular capsule
we have two main ligaments that I want to make sure that you understand you've probably heard
of these before particularly if you are into sports or have played any sports your ACL and
your PCL so anterior cruciate ligament so you can see the anterior cruciate ligament here in
the more anterior view and your posterior cruciate ligament which you can see more
clearly in a posterior view as the names would indicate so think about it if you have ever heard
of either of these ligaments which one have you probably heard of more which one comes up
more that's going to be your ACL and the reason that is it is because it is significantly weaker
and more often damaged now important to note and this is sometimes confused a lot of some
textbooks traditional textbooks had that the ACL was attached to both the tibial collateral
ligament and the medial meniscus it actually isn't is very closely associated but they're
not actually attached but oftentimes those three components are damaged together and if you've ever
heard the term terrible triad terrible triad or unhappy triad what's being damaged is the TCL
the medial meniscus and your ACL now often times only these two will be damaged but if all three
are damaged together in one particular injury that's the terrible triad so if you think
about somebody running into your knee from a lateral side that force is going to move all
the way to the more medial side and damage those things that are attached or closely
associated to one another all right PCL you may have heard of this particular ligament as well
it is considerably stronger than its partner on the anterior side and this is really important
in terms of actually when you're walking downhill or walking down stairs this is the ligament that's
keeping that femur from moving too far from where it should be okay so it's really keeping
it in check allowing for the appropriate amount of flexion and extension but not allowing for
that femur to get too far out of place so it's a important in terms of locomotion it's less likely
to be damaged if it is damaged it has bigger implications than the anterior cruciate ligament