Transcription
Starting with the knee, just kind of going over the protocol. We have two sagittal sequences. One you can think of as being fluid sensitive. The other one you can think of as being kind of more for an anatomical kind of evaluation and looking at the actual marrow signal. And then we have the exact same thing for the coronals. One is going to be a fats saturated fluid sensitive and then the other one is going to be something that you can use to evaluate the marrow signal and take a closer look at the anatomy. The additional sequence that we acquire is going to be an axial fat saturated fluid sensitive sequence as well. And I'll kind of run you through kind of my search pattern um as a basic approach to these knee examinations.
So the first thing I like taking a look at is the quadricep tendon. You can see it kind of has a striated appearance here distally. That's because there are four muscles which contribute to three slips that converge distally to form this single tendon. Those muscles are going to be the rectus femeris, the vasis intermedius and the vasis mediialis and lateralis muscles. So you can see here this is the quadricep tendon. And we just kind of follow it down as it inserts on the patella. And you can kind of see the striated appearance here. So to call pathology, you really want to see kind of a higher uh threshold of signal abnormality that maybe disproportionately uh involves the more medial or lateral fibers as you go distally here.
The next thing I like taking a look at is the patellar tendon which is going to be coming off the inferior aspect of the patella here. And we kind of follow that down here as it inserts on the tibia. And taking another look here on the sagittal, we can see the patellar tendon here as well. So the important concept for this is going to be a lot of times this can be difficult to evaluate because we get a lot of artifactual increase in signal um particularly proximally in the patellar tendon on these proton density sequences. And this is going to be an important concept in msk imaging which is magic angle artifact. So the tendons are composed of collagen and when collagen is directed at a 55° angle relative to the magnet board you get an artifactual increase in signal particularly on the proton density sequences. The classical teaching is you should use this sagittal T2 to see if the signal persists here. But when you're just starting out, it can be kind of difficult to really gauge what true increase in signal is on one of these unsaturated um sequences. So what I like doing is I look for kind of ancillary findings. Is there a lot of prepetellar subcutaneous edema? Is there an external marker? And then the actual morphology of the tendon itself. Is it abnormally thickened or is it abnormally flattened in morphology?
So once I'm done taking a look there, I kind of boost open this um axial and then I run a lot of structures on here that we're going to end up looking on the satchel and the coronal as well. The next structure I like taking a look at is the poplius. So you can see it's the deepest muscle kind of down here and then you kind of follow it to the myotenous junction to see the actual poplius tendon and you can see the several tendon fibers here as they coales into this tendon that we see right here. and then I follow it as it curves around and inserts into this lateral femoral condor notch. As the tendon is turning, it tends to have a little bit of this artifact increased signal abnormality. So, it's definitely one of the additional structures that you want to increase your threshold for calling an abnormality. A lot of the true abnormalities that you'll see with the poplidius tendon will be edema in the actual muscle belly, which will suggest that there's an evolving poplidial myotenous strain.
This next structure I like taking a look at on the axial is going to be the lateral collateral ligament, which is going to be this structure right here. It tends to also kind of have a little bit of a heterogeneous signal proximally. And then we'll follow it um as it extends inferiorly to the fibular head here. And then I do the same thing on the medial side, taking a look at the medial collateral ligament. So what's going to be important on the axial is making sure you follow it inferiorly enough where sometimes you may see some distal periamentous edema which can be a more subtle sprain involving the medial collateral ligament.
Then we're going to take a look at all of these posterior medial structures here which are going to be the test tendons and muscles. And kind of an a good pneummonic to remember these is going to be se grace to t which is going to be sartorius graasilus semiendinosis and then the one that's left over is going to be your semimebrosis and then I like following this distally and we can see this is now the semimebinosis tendon and it'll fan out here to insert more distally and then the next thing I take a look at is uh is there a popial cyst or And this is going to lie between the semimebrosinosis and the medial head of gastronmus. You can think of that as M&M for these two structures here. Um then the next thing we're going to look at are the cruciate ligaments. You can see the ACL right here in the intercondular notch and we're following it as the tendon fibers kind of spread out here. So that is going to be intact. Same thing with the PCL here where we can follow it and it's clearly um contiguous without a tear.
Then we're going to kind of get into talking about the cartilage. And there are numerous kind of different kind of approaches to this. There are actual conrosis classification schemes where you may say that something is grade 1, grade two or grade three. I tend to be a little bit more descriptive in my approach to cartilage starting all the way from kind of what I would consider to be minimal or almost no uh conjures to something on the higher spectrum which is going to be high-grade or kind of like true um cartilage loss. So starting with that kind of minimal end of the spectrum, really what you're going to see is just kind of like a heterogeneous kind of appearance to the cartilage. And when you look at the actual surface, you'll see stippling or kind of what I refer to as surface irregularity in this case. I mean, this looks pretty smooth. Um, there really isn't a lot of cartilage abnormality here. Just a little heterogeneous kind of appearance of the cartilage that you can see. And then kind of in the middle kind of category, we're going to start talking about fissering, which you're going to be looking for linear bands of bright or dark signal. Superficial, it's kind of halfway down. Deep, it's going all the way down to the bone surface, which is going to be this black line here, which denotes the cortex of the underlying bone. And then all the way on the high end of the spectrum, we're going to start talking about true cartilage loss. So, does it look like chunks are actually missing? Partial thickness or full thickness which the entire piece of cartilage is missing from the underlying bone. Then you can also comment on if there is underlying marrow edema or developing subcondrial cystic change as well.
So you can think of the patella as having three different locations. There's going to be the medial aspect of the patella, there's going to be the median patellar ridge and then there's going to be the lateral patellar facet. A lot of times what they like doing on test questions is you're not going to be able to scroll down and see the fibula. So how do you denote what is medial from lateral? You look at the morphology of the patella. The lateral patellar facet is going to be longer than the medial patellar facet. And that's kind of how you can see which side is medial versus lateral. So looking at the tlear cartilage here, I like taking a look on the axial first to kind of form. All right. What do I think is going on with the tlear cartilage? And then confirm on the sagittal. As you can see, it's a curved structure. So, as we're cutting through it on the axial, you can volume average it. So, you just want to kind of confirm, all right, am I underalling or potentially overalling a cartilage finding on the sagittal here.
One of the common knee pathologies is going to be the concept of patellar malt tracking. And it's really a constellation of abnormal imaging features. One of which being is there prominent superolateral hafa fatpad edema. What I recommend doing is looking for where the lateral patellar cartilage touches the lateral tlear cartilage and then go one to two slices down. There should be obvious edema in this kind of uh area of the fat here to really be calling that superolateral edema. Other things you look for is is there lateral patellar tilt? Is the patella sublocks out of the tlear groove? Is the tlear groove itself shallow in appearance? So, this isn't as deep as it should be. And one of the other things we talk about is measuring a TTG distance. What you want to do is put your cursor in the tlear groove. Scroll down and keep your cursor there. And you're essentially going to measure this distance over to kind of the center of where this patellar tendon is kind of inserting like this. So this is kind of like in the lower portion of the borderline range. 15 to 20 mm is a borderline increased TTTG distance.
So after we've done this, we're going to kind of move into evaluating the medial and lateral compartments of the knee. I like looking at the medial compartment first. And as you can see here, kind of one of the important structures is going to be the meniscus itself. Think of this as being kind of a bow tie uh appearing structure where you have two triangles that are kind of um opposing each other. And think of the meniscus as having five distinct components. There's going to be an anterior root, there's going to be an anterior horn, there's going to be the body, there's going to be the posterior horn, and then there's going to be the posterior root as well. So when you're looking for abnormalities in the meniscus, what denotes a meniscal tear is going to be signal abnormality within the substance of the meniscus that extends to an articular surface on two consecutive slices. Outside of that, you look for the morphology of the meniscus itself to be abnormal to suggest if there's an underlying tear.
So for the big categories of meniscal tears, kind of one of the more common things that is intuitive is going to be the horizontal or oblique tear, which is going to be on the sagittal kind of linear or kind of a horizontal line that extends to an articular surface. The other big category of tear is going to be your vertical or longitudinal, which is what we call bucket handle tears. And I feel like in a lot of these, what you're looking for is actual loss of miniscal substance, which is a term I like using. It can be the posterior horn. It can be the anterior horn. But it looks like a chunk of the miniscus is missing. And a lot of times that's due to it flipping over or tearing and having a displaced miniscal flap fragment a lot of times which you'll see in the intercondular notch. In this case, we don't see that. This is a pretty good-look meniscus that's pretty low in signal and there's no abnormal morphology. The other big category is going to be the radial tear. And the concept here that is going to be important is is there blunting of the inner margin of either the posterior horn or the anterior horn. What that means is this triangle should have a pointed edge. If this goes away and it looks like there's a shelf that's blunting the inner margin of the horn and the meniscus, which can suggest that there might be an underlying radial tear. If you see that, what you want to do is you go to the coronal. And what you're really looking for is is there a cleft here that corresponds with the area that's blunted. If you see that cleft here that lines up with blunting of that margin, that's going to be 100% a radial tear. So that's kind of how you look for one for the horns. For the body, it's going to be kind of the opposite. What you'll see is a cleft on the sagittal and then on the coronal. As we come into the body here, you can see the body looks like a triangle. on the coronal. This will be blunted.
So after following the meniscus here on the sagittal, I take another look here on the coronal. So we come anterly. This is going to be the anterior root. Then we're coming into the anterior horn. Then you're coming into the body. Then you're coming into the posterior horn. And then you can really take a good look at the posterior root here. So what's going to be really important is you don't miss a subtle underlying root tear. A lot of the meniscus ability to kind of weightbear is going to come from integrity of the root. So it is very important to mention if this is torn.
The other thing I like doing on the coronal is taking a look at the MCL. You can see it's nicely laid out here. And so when we talk about ligaments, we use the terminology sprain which will correlate to essentially is there a grade one sprain which would be low, grade two moderate or grade three highrade sprain. Grade one there is just going to be peril ligamentous edema. Grade two there's going to be actual signal abnormality within the ligament itself. Grade three is going to be full thickness discontinuity of the ligament. often times what becomes difficult with the MCL is going to be is it grade one or grade two and in that case the axial can be helpful to kind of look at the more anterior components versus more posterior components to see if there's actual signal abnormality within the ligament itself.
The other thing you want to do as you're looking on the sagittal and the coronal is take a look at the cartilage in the medial compartment. So you're going to have cartilage along the medial femoral condile and the medial tibial plateau. kind of a way to kind of divide this is think of this as being anterior articular. This is central articular. This is posterior articular. And this is a bit of a misnomer referring to this as posterior non-articular cartilage here. If you bend the knee, this is going to roll down into the actual joint space. But this can be a common blind spot for um people that are just starting. So you don't want to make uh miss a cartilage abnormality up here. And then do the same thing on the coronal. kind of just run the medial tibial plateau cartilage and the medial femoral condular cartilage as well.
After that, we're going to move into the lateral compartment and we're going to do a similar thing with the lateral meniscus. As you can see, this is pretty low in signal. Looks like a bow tie as you can see here. And then we're going to kind of get into the different components. Anterior root, anterior horn, body, posterior horn, going all the way into the posterior root as well. cartilage we can see here following it all the way to this kind of posterior non-articular cartilage and looking along the lateral tibial plateau as well. Then we'll go over to the coronal and you can see this is going to be the anterior root. We're coming to the anterior horn. This is going to be the body. This is the posterior horn and you get a good look at the posterior root that's coming back here as well.
The next thing we want to do is run all of the kind of more important or critical lateral compartmental structures. Think of this as kind of moving anterior to posterior. You can see we're more anterior here. The first structure that you see coming down here is the ilot tibial band. And really what you're looking for the axial can be helpful here. This is the IT band. You're looking for edema deep to the ilotibial band and superficial to the lateral femoral condile. This is a common pathology in runners which we refer to as ilot tibial band lateral femoral condile friction syndrome. The next structure as you start to move more posterior is going to be the lateral collateral ligament which is where my cursor is here. As I previously mentioned a lot of times proximally it'll look a little thickened and you'll see this heterogeneous signal which is going to be kind of within the range of normal. You got to you're going to want to increase your threshold for calling an abnormality with the lateral collateral ligament. And we can see it kind of going down here to the fibular head. The last structure as we move even more posterior is going to be the biceps femmeris. This is the actual muscle here. And you can see this is the actual tendon that's coming down to insert on the fibular head here which in this case it looks normal as well. So we talked about the pest structures sartorius graascillus semieninosis semimebinosis. This is going to be biceps femmeris that's here on the lateral side which we can see on the axle. You can follow it all the way down here as it's inserting onto the fibular head.
Now really the last thing that you want to do is take a look at the cruciate ligaments again. So we can clearly see the PCL is intact here coming across and then we're taking a look at the ACL which is coming down here and this looks intact as well. As people get older you can get a little bit of increased signal within the cruciate ligaments which is something we can refer to as mucoid degeneration. Outside of that I take another look at you know just the subcutaneous tissues. Is there any edema that I didn't see or fluid or um subtle signal abnormality in any of the other muscles? So we can kind of see um a portion of the vasis mediialis here. This is the vasis lateralis over here. And then as we come down this is medial headastronmus and this is the lateral head of gastronmius. And you can see a little bit of the solius muscle as we start to come down a little bit more inferiorly here.