So, let's talk a little bit about anterior knee anatomy and what's important in terms of factoring in an ultrasound of the anterior knee. I think the first thing to keep in mind is positioning. You want to be well positioned yourself as a provider. One of the things that I really like to do, and this is up to many, there's a fair bit of difference between providers who do this, but I'd like to involve my patients in the ultrasound experience. I think it gives them a lot of buy-in in terms of seeing the structures that you're seeing, having you walk through their evaluation with them, and it gives them a sense of extra care, and I've found that to be very beneficial to the therapeutic bond and relationship. But one thing you want to make sure is that you have the knee that's being evaluated also in the right position. So, having that knee with a towel roll or two underneath the knee will help put it into a 20 to 30 degree flexion, which will then allow you to better evaluate some of the structures we'll be talking about. Now, there's a couple other evaluation methods which we can go into, but generally that's the position which will get you the most bang for your buck as you evaluate. As always with ultrasound, you want to try to see things in orthogonal planes, so in short and long axis, and obviously you want to factor in your key structures when you're doing an anterior knee evaluation and trying not to miss structures that might be causing that pain. And I tell my learners that really no matter what you do, be it a physical evaluation or an ultrasound, I have people essentially do as comprehensive an evaluation as they have time for, and ideally a full comprehensive evaluation, because you may be led down the wrong path. For example, if somebody has what you think is patellofemoral syndrome but turns out to be saphenous neuropathy, those present very similarly, and you might miss one if you don't scan high enough to evaluate the saphenous nerve, so something to kind of factor in when you're sort of building both a basic and an advanced ultrasound skill set. So as I mentioned, positioning, this is just a picture of what a typical patient's knee might look like without the towel rolls below them, but that position there, and it'll give you an image that looks more or less like this if you're in that long axis, with this particular case being an evaluation of the quadricep tendon in this area. So as I mentioned, orthogonal views. Here's a demonstration of what orthogonal views of the patellar tendon would look like. Hopefully this is a scan that you guys are all quite familiar with. On the left, you see the image of the patella with the patellar tendon approaching it from the right side of the screen towards the left. One thing to keep in mind that the examiner here did quite well was they positioned the probe in a manner which you lose anisotropy. In many instances, the patellar tendon, because it curves as it approaches the patella, if your probe is sitting flat upon somebody's skin without adjusting, you may come across anisotropy, which may lead you to a diagnosis of pathology when there's no pathology there. Another way to kind of contend with this is just to play around with your probe position to see if you can correct for any potential anisotropy and determine if what you're seeing is truly pathologic or not. And then again, seeing things in orthogonal planes, you see in the picture to the right, a cross-sectional view of that patellar tendon, which allows you to potentially miss pathology, to avoid missing pathology that might not be in the plane that the long axis view was obtained in. So for example, you can see, I don't know if you can see my pointer, but there's a little lesion here that if you sliced and just did a longitudinal axis view through this plane, you might miss some pathology in this area. So something to factor in. So key structures. I think this is sort of the meat and potatoes of this talk. But the idea is that when I divide up the anterior knee, this is sort of how I go about doing it. I think about structures superior to the patella. And then as I'm scanning inferiorly, I move to the superficial aspect of the patella, so making sure not to miss overlying the patella. And then looking a little bit more anteromedially and anterolaterally, and we'll go through that, but there are far more evaluation methods to dive into if you're focusing more on the medial or lateral knee. We're going to really keep it to the anteromedial and anterolateral knee. And then we move to inferior to the patella as well. In many instances, if the pain is more vague than truly anterior knee pain, I might do a posterior knee ultrasound as well, depending on what time and what their patient's presenting symptoms look like. But I'm not going to be covering that here, hence the parentheses. So let's talk about the superior patella. This is a GIF image of a quadricep tendon here, and I will pause this guy. Oops, didn't let me pause. All right, well, I guess I'm not pausing it. There's a few findings here that we can go into, but the key findings and key structures you want to look at superior to the patella are your quadricep muscles, the four parts of your quadricep, as well as the tendon. You want to do a careful evaluation of the suprapatellar joint recess, which is essentially just proximal to the superior margin of the patella and underneath the quadricep tendon, where you see a number of relevant structures and may help guide relevant procedures. You don't want to miss your bony structures in case there's any concerns or issues there. And then obviously, considering your neurovascular structures as appropriate are your key structures. So getting into the quadricep muscle and associated anterior knee musculature, this is a cross-sectional view of the quadricep, which I think is a pretty classic view if you kind of place the probe mid-thigh. And you can see the four parts of your quadricep here with your rectus femoris, your vastus medialis and lateralis, and then your vastus intermedialis with the femur below. So evaluating this structure might be relevant if you are worried about somebody who has a traumatic quad injury or a remote injury that is presenting as quadricep pain or thigh pain, basically. This position is pretty standard, but if you shift the probe so that your vastus medialis, which is in this quadrant here on this picture, is now taking up more of the screen, you then come across the sartorius and eventually you'll start to get into your adductor muscles here. So this is a picture where lateral is here and medial is here, which is a common probe positioning strategy. And you still see your femur in both of these images. But if anybody is aware, here you see these two sort of documented substructures here. Normally I'd ask what those structures are, but I'm particularly curious about this. We've alluded to it a few times. But at the intersection of the vastus medialis and the sartorius is your saphenous nerve. And once again, the saphenous nerve is a structure that can present when irritated as anterior or anterior medial knee pain. It has branches that turn into the genicular nerves, which feed the joint and provide symptomatology in some instances. So in many instances, you can even develop a skill set to do procedures such as radiofrequency ablation. One of my former fellows is doing RFA in our practice now and is teaching our fellows to do RFA for genicular nerves to manage people with chronic knee pain, be it arthritis-related knee pain or refractory things like patellofemoral knee pain. So know that the saphenous nerve sends out branches that are relevant to knee pain. And once you get into evaluating nerve anatomy, neuroanatomy, the saphenous nerve is relevant to this particular evaluation as well. So a diagram of a long axis view of the knee is as such. This comes from, I think, the FP notebook, but these are kind of nice ways to kind of diagram what you might be looking at. In the superior aspect of the knee, above the patella, you have the patella here as your big landmark, which you can anchor upon. And obviously, the quadricep tendon is going to be the first muscular myotendinous structure that you may come across. But below that is your suprafatellar fat pad and your prefemoral fat pad. And we'll kind of go through that in a bit. But those may not be easy to distinguish one from the other in some instances, depending on how the patient is presenting. But if they have any evidence of fluid buildup, say a fluid in the suprapatellar bursa, which is contiguous with a joint, you will see fluid in that bursa, which will then separate out those two fat pads. And so this is a diagram of effectively this image here. So here it's sort of flipped, but you see your patella on the far left here, and your quadricep tendon overlying the top of the screen in long axis. And then you might be mistaken here in saying, oh, gosh, they have a big effusion here. You can see this hypochoic anechoic structure that looks well-defined. This is a suprapatellar effusion within the bursa. But keep in mind that you actually have two fat pads here, between which the fluid that may come from the knee will accumulate. And that's why people develop effusions that are more noticeable in the superior aspect of the knee when they have an effusion developed from arthritis or trauma. And a lot of times I've had fellows take a look at this structure and think this was just synovial proliferation, essentially synovitis from the trauma or from the issue at hand. But this is actually the suprapatellar fat pad right here, also called the quadricep fat pad, depending on which context you are referring to. And then down here, just adjacent to and superior to the femur is your prefemoral fat pad. So once again, we're seeing our quadricep tendon, our suprapatellar and prefemoral fat pads, as well as our suprapatellar bursa here in this structure, all seeable via long axis and particularly clear in individuals who have an effusion. So if you turn your probe on short axis, one maneuver I do is I move the knee patient's position from a 20 to 30 degree flexion to a greater flexion. So they're almost like their knee is almost fully bent and their foot placed on the table. So they have a strong degree of knee flexion. And that allows you to have an evaluation of not only the quadricep tendon, but also this structure down here, which is marked as C and F here. So this is your femoral trochlea here. And this is the cartilage stripe along that trochlear groove, which can be relevant to evaluating conditions such as arthritis. And we'll get into that a little bit later. But this is a nice view when you're in orthogonal axis to look at the cartilage with the knee in more than 20 to 30 degrees flexion, because you may not be able to bring out the trochlear cartilage without that degree of flexion. So that is the approach. Some quick hitters before I finish up. Quadricep tendon pathology can look like this. So individuals with quadricep tendon pathology can often present similar to patellar tendon pathology, just superior to the knee. This is a case of calcific tendinopathy or calcific tendinosis, which you can see the arrow there, this hyper-echoic stripe that's lining up along the long axis of this quadricep erectus femoris part of this tendon. Then you see a little calcific deposit in short axis as well. These are problems that are amenable to treatments such as Tenex or even lavage, depending on how dense these structures are. You can see that this particular calcific deposit is not hard enough to cause a true echo shadow that eliminates the border of the bony structures here. So just be aware that that's something that might be amenable to being removed, and we actually did that. Here's a case of a traumatic rupture of the quadricep tendon. So you see that you've lost that fibular architecture. There's a gap in the tendon here. There's often a lot of ground glassing in the region, which suggests bleeding, but can also obscure your clear imagery of this area. So just be aware that traumatic cases can be somewhat limited in ultrasound, depending on how you're doing and what you're looking for based on the lack of organization of the tissue being involved. But being aware that the lack of organization of the tissue then lends itself to the diagnosis that you might be considering.

2nd Edition, CASE 54

2nd Edition

Thigh

anterior knee anatomy

ultrasound evaluation

saphenous nerve

calcific tendinopathy

quadricep muscles