and we'll start with bone. Bone's really quite easy. It's hyperechoic. It's well-defined. And again, this is shadowing behind the bone. This is not actual bone, as you might imagine in an MR. And we see this both on long and short axis. Really, it's the bone. It's the road map when we do joint injections to understand where we are in the joint. Tendon is also hyperechoic. It has what's called a fibular echo texture. And we can see the individual collagen bundles. Again, just amazing spatial resolution with tendon and superficial structures. On short action, it has a homogenous stipple dot appearance. Ligament is similar, but it's more compact. So we call this a hyperechoic compact fibular echo texture. And on short axis, we often use a starry night appearance, although I think we have to be somewhere now back of Australia to have stars everywhere. So I'm not so sure about that. Muscle has a greater water content. So it's hypoechoic in relation to bone, in relation to tendon, in relation to ligament. So we can see the hypoechoic background, which is the muscle fascicles. And then we see the hyperechoic striations, which is the fibroadipose septae. So here we see a short axis of the elbow joint. This is the humerus. And then we can see the hypoechoic muscles, pronator teres, brachialis. We see the septae, which is hyperechoic, in between. And then we see the hypoechoic articular cartilage of the humerus. Ultrasound has been a game changer for nerves. The resolution of nerves on MR is not that great. It's excellent on ultrasound. So here in long axis, we see hypoechoic parallel lines, which correspond to the fascicles of the nerve separated by hypoechoic bands, again, corresponding to the perineurium. On short axis, we see a honeycomb appearance. And then we can see the hyperechoic perineurium and see this nerve very well-defined. And so it's proliferated a whole slew of ultrasound-guided procedures with nerve. All right, I just want to mention one artifact. There's many artifacts in ultrasound. But I think we should be aware of one of them. And that's the artifact of anisotropy. Anisotropy occurs when the sound waves are not fully perpendicular to our target structure. And when that occurs and we have a slight angulation, then those beams are deflected and scattered. And so its return back to the transducer has muddied the information. And so what that looks like is, so here we see a cross-section of the patellar tendon. It's hyperechoic. It's well-defined. And I'm going to take my ultrasound probe and wag it back and forth. And what we see then when I wag it back and forth is it becomes hypoechoic. That information gets scattered back to the transducer. So anisotropy, you'll see in the lab. It's an important artifact to consider, understanding that one of the ultrasound findings of tendinosis is hypoechogenicity. And so it's important to distinguish between pathology and an artifact. Now, sometimes we can use anisotropy to be our friend in that different tissues have different susceptibility to anisotropy. So tendon is the most susceptible. And nerve, for example, is less susceptible. So here we are in a short axis in the carpal tunnel. We can see the median nerve at the apex here. We can actually see that because different tendons take a slightly different path within the carpal tunnel, for example, the flexor pollicis longest here, it appears hypoechoic or anisotropic compared to these other tendons. So as I, again, wag the probe back and forth, we see that while there is some anisotropy of nerve, it's mostly the tendons that are affected and it can be used to distinguish the boundaries of the nerve. All right, so we'll take a couple steps in obtaining an optimal ultrasound image. So we're gonna pick up the probe, we're gonna set it down, and we're gonna try to get the best image possible before our ultrasound guide and injection. And the first step in this is our probe selection. And there's two types of probes. One is a linear array probe. One is obviously named, and the other is curved linear. Linear array probes emit a column of sound waves, whereas curved linear will scatter them or fan the sound waves. Therefore, curved linear probes can go deeper. So abdominal ultrasounds, often pelvic ultrasounds, use linear array probes. An MSK ultrasound, we typically use them with large patients for hip injections. Occasionally I use it for a shoulder injection. But the technology of ultrasounds getting better that I would say that 95% of my work I can do with a linear array probe. There's also short footprint probes. We call this in Minnesota, for obvious reasons, hockey stick. And that is better for superficial structure. It's also nice to have a narrow footprint when you're doing ultrasound guided procedures. Now, these probes emit a bandwidth or a range of frequencies rather than just one frequency. So we see on this probe, this is a linear array 12 to five probe. So it's emitting frequencies from five to 12 megahertz and et cetera. Why is that? Well, there's a tension with ultrasound waves, and that is that the higher the frequency, the better the resolution, but the less the depth, the lower the frequencies, the better the depth, but we lose resolution. And so we compromise with these probes. And so certain probes we know we use for superficial structures, other probes for deeper structures, but they always have a range. In some machines, depending on a sophistication, we can even hone that in even further. So let's take an example of this. So this is the patellar tendon. So to the left of our screen is the patella. This is the tibia. This is a curved linear probe. And you can see, I can see the big picture pretty well, but not a lot of detail of the patellar tendon. So if I wanted to look deep in Hoffa's fat pad, maybe this would be the choice. The linear array 12-5 probe gives much better resolution. So in general, a linear array probe has better resolution than a curved linear probe. I can start to see the individual fibular echo texture of the tendon itself. I see some depth. And now if I switch to the 17-5 probe, I start to see better resolution of the tendon, but I'm now starting to get magnified and honed in. So I guess it basically depends on what your goal is. So if I'm gonna do a procedure on a patellar tendon, I obviously wanna focus in on it and use a high-frequency probe. If I'm doing a hip injection in a large person, then I'm using a low-frequency probe. So this is the image we obtain for a glenohumeral joint injection. Get just to hammer home this point. So this is the posterior glenohumeral joint. This is the humeral head. This is the acetabulum. This is the posterior labrum. This is a linear array 17-5 probe. And we lose a fair amount of detail. Whereas if we switch to the 12-5 probe, again, because of those lower frequencies, we get a fair amount of detail, but we have enough higher frequencies to get good resolution. All right, then there's three settings we should be aware of on the ultrasound machine to optimize our image. The first is depth. And the structures get smaller as the depth increases and vice versa. So we go back to our patellar tendon here, and this is optimal for just scanning the patellar tendon. And the depth is not too great to lose the resolution we want. So here we see less optimal. So I'm certainly seeing down in Hoffa's fat pad, but now the tendon is smaller and I lose detail. Again, if I'm doing a procedure, I may even reduce the depth further to get more detail of the tendon as I hone in on it. This is the anterior band of the glute med tendon. And we can see there's great resolution here. This little dark hypochoic line is a greater tocanteric bursa. And so if I'm doing a procedure on the glute med tendon, I'm going to hone in on it. But we know that tears start as undersurface tears. And so I want to increase the depth, see the big picture, and see the whole musculotendon disjunction on the anterior band here. The second setting is focal zone. Most machines now we can adjust the focal zone. And the column that comes out of a linear ray transducer is in the hourglass morphology. And it does focus at a certain height. But there's a range where we're getting good resolution from our ultrasound frequencies. And we call that the near zone, the focal zone, and the far zone. And essentially, your target structure should incorporate those zones. And then we have a dead zone both directly under the transducer and deeper down. Typically, I would like to put the focal zone just deep to my target structure. So we go back to our posterior glenohumeral joint. And in this machine, a focal zone is actually arranged so we can adjust both the depth of the focal zone as well as how broad it is. And so here the focal zone I set fairly superficial. And you can see here that we lose some resolution of the glenohumeral joint. I bring the focal zone down. We gain resolution. It's fairly broad. And so if I want to hone in on the details of that joint, then I'm going to set my focal zone just below that joint and say if it's a tough injection. And then the last setting is gain. Gain is brightness. It's the amplitude of the sine wave. And brightness is directly related to contrast. And there's contrast that we need to see the structures. And so as we turn the gain up or turn it down too low, we lose information. And it's an easy setting. Now, gain can also be adjusted in terms of time at the signals are transmitted and come back to the probe. And essentially, it's adjusting gain at certain depth. So it looks like an equalizer on most machines. So here is the sinus tarsi. So we have the anterior process of the calcaneus right here. And I can see the entrance of the sinus tarsi pretty well. But if I want to look deeper in the sinus tarsi and I just turn up the general gain, it's going to get too bright at the entrance to get the information I want deeper. But I can use the TGC to adjust the gain at different heights and to optimize my image. And this will come into play with hip injections and occasionally larger people and glenohumeral joint injections. So optimization starts with probe selection. And there's three settings that we should be familiar with with the machines, depth, focal zone, and gain. All right, I mentioned the Doppler imaging on ultrasound machines. And Doppler imaging detects motion. There's various types of Doppler. But most modern machines now will use color Doppler. When I first started ultrasound, there was also power Doppler that did not detect direction, but just detect motion. It was more sensitive. But now the machines have gotten to the point where color Doppler is adequate. And so color Doppler detects both speed and direction of flow, in this case, vasculature. So if it's going towards the probe, it's going to be red. And if it's going away from the probe, it's going to be blue. So if we look at the radial artery here, I'm going to, again, wag the probe back and forth. And now it turns blue because it's going away. I wag it back towards the proximal part of the arm, and it turns red. A second setting with Doppler we need to be aware of is the gain. Again, we're looking for vasculature when we're doing procedures, ultrasound guided injections. And so if we have the gain turned up too high, we're going to get artifact. And it could be full. There's vessels when there's not. If it's down too low, we may miss vasculature that we would go through. So basically, what we want to do with gain is adjust it so we don't get artifact, we don't get noise, but we fill the lumen of the vessel. So here we go. So the gain is up. We see all this noise. I'm going to turn the gain down. And it fills the lumen. This would be optimal. If I keep going, the lumen now is not getting filled, and so forth. And then the last thing I want to say is annotation. So if we're doing ultrasound guided injections in the office or, in my opinion, anywhere, we should save the images. We should document what we're doing. If we're billing for an ultrasound guidance, we need to document what we've done. And so annotation becomes important. And my feeling on annotation is not to overdo it. We don't want to spend and label everything on an ultrasound image. But we should be able to, anybody familiar with ultrasound should understand what this image is showing. So here is the third tarsal metatarsal joint. This is just prior to an injection. So these are my pre-injection images. And so I put the location, right foot. It's a long axis. And I put the third metatarsal. So of course, then, this is the lateral cuneiform. I switched to short axis. And again, it looks like a glob of a lot of things. But to sort it out, this is the third metatarsal. This is the second metatarsal. This is a dorsal pedis artery. So this is why I got this image to document where it is and plan my injection. So really, this is all the information that's needed, which doesn't take very much time to properly label your images. All right. So in summary, we want to be familiar with the sonographic appearance of various structures within the musculoskeletal system and become comfortable with choosing a probe and optimizing an image. And then we're going to just move into ultrasound guide injections. I still work at the same place, as far as I know. But I do have one additional disclosure in that I do live in Duluth voluntarily. So the goals of this are to understand the principles of ultrasound-guided injections, understand the process of performing an injection, and then we will go over specific ultrasound-guided injections. All right, so why use ultrasound guidance? Prior to essentially changing my focus of practice to MSK ultrasound, I estimated I had done 40,000 palpation or landmark-guided injections. We did lots of them over a course of 20 years. And I thought I was pretty good. And it turns out I wasn't as good as I thought. So I've just included level 1 and level 2 evidence. This is the upper extremity. This is lower extremity. And this is the accuracy of landmark-guided joint injection. I just want to point out a couple of things on this slide. First is the shoulder. So one out of three to one out of four times in experts' hands, we're not getting into the joint. Go to the knee. We think we're pretty good at the knee. This is from the orthopedic surgery literature. And one out of four to one out of five times, we're not getting in the knee when we're not using image guidance. That's a pretty high number when we're going through all this effort to obtain orthobiologics. People are paying cash. So I throw that out there that even though we think we're pretty good, we may not be as good as we think we are. So what are the principles of ultrasound-guided injections? When we approach and we're going to start to do these in the office setting, what should we think about? Well, the first is ergonomics. And just like surgery, you want the setup so it's comfortable. If you're running the complications, and anticipate longer than you, or you're there longer than you anticipated, again, you want the ergonomics set up properly. It's the same thing with ultrasound. Sometimes when I rush and do an injection, and all of a sudden it's just not working out, I'm like, oh, jeez, why didn't I take the time and set this up properly? So this is the setup we use for a hip injection. And what I like to point out in our ultrasound setups that the table, the chair, and the ultrasound machine, both the screen itself as well as the console, all can be adjusted in heights, at different heights. We all have our own preferences. And so if I'm scanning the right hip, let's say getting the pre-injection images, planning my injection, I'm going to be comfortable. My hand can easily be on the ultrasound machine to optimize the image, to annotate without a lot of twisting or turning. If I'm just doing a diagnostic ultrasound, it's easy just to reach across and do that from this position. But if I'm doing an injection, then that's not very ergonomically sound. So I'm going to move the table out. I'm going to go on the other side, and my sonographer will go and run the machine for me. I also want to just make a comment on how we hold the probe. Most beginners oftentimes hold the probe without touching the patient. And I always say, you just got to get down and dirty. You got to get your handful of gel. It's really important when doing ultrasound-guided injections and procedures that you touch the patient and provide a stable base. It's easy to slide off during an injection with the gel. It's slippery. Sometimes you're making just the most minute of adjustments, and it can easily be accomplished if you have a nice, firm base. And then you can just use that to make small changes. I also just want to mention that sometimes with ultrasound-guided injections, we don't quite get the angle we want. And so there's something called a standoff where we take coupling gel, we glob it on there, and we can angle the probe. And now we can adjust the angle that we enter to get to our target. And I'll mention that a couple of times with some of the specific injections.

ultrasound imaging

joint injections

tendon characteristics

nerve resolution

ultrasound-guided injections