Hi, I am Kathy Bithock. I'm an associate professor at Rocky Vista University. I'm going to be doing an ultrasound consult today on metatarsal fractures. My co-author for this is Alyssa Goldstein. Ultrasound may not always be our imaging modality of choice for fractures, but if you're doing ultrasound, you certainly are going to see fractures. In a case like this, I would first palpate the area of tenderness. I would use a linear transducer, something with a high frequency as this is a superficial structure. If you are looking for a possible fracture of a deeper structure, I would use a transducer with a lower frequency. When we are imaging over bones, we always need to remember our artifact of posterior acoustic shadowing. We cannot see deep into the bone because of this artifact. Anytime you have this hyperechoic area, which is the periosteal edge, you will get a shadow deep to that. It is also useful to think about the type of fracture that we are dealing with. It's going to be a little bit easier to see a traumatic fracture under ultrasound than something that's caused by overuse. Stress fractures oftentimes are non-displaced. They can be very difficult to diagnose both on radiographs and on ultrasound. And so sometimes we need to use MRI for those, but traumatic fractures oftentimes we will see on ultrasound. Here are some examples of non-displaced fractures seen on ultrasound. You can see in the image to the left that you have the joint space and then you have the non-displaced fracture seen near that area. On the right side, there's a fracture of the epiphysis. Also notice that around the fracture site, you get a little hematoma, which kind of causes this periosteal lift or this anechoic space just superficial to the fracture area. Here's an example of a displaced metatarsal fracture seen under ultrasound. And you can see the step-off area as well as some periosteal lift in the same area. How do we differentiate fractures from normal structures that can look like fractures under ultrasound? One area is gonna be the joint space. If you are in a joint space, you will see nice rounded edges and a fracture line will often be sharp edges. There will also be an area of periosteal lift often seen near fractures, but not near joint spaces. Another area that can be difficult to differentiate from a fracture is the physis. These will have a rounded edge and they can have a hypoechoic area that is just the cartilaginous physis, but they will not have a true periosteal lift, but that can be hard to differentiate. One of the best ways to differentiate this from a fracture is to simply use the contralateral side for comparison. With any imaging modality, you should always know your limitations. With fractures, sometimes we can see bone irregularities that will mimic a fracture such as vascular channels or physes. Stress fractures can easily be missed because we don't see the step off and it's not as obvious. Also be aware of artifacts, slow blood flow. How do we know the accuracy of using ultrasound to diagnose fractures? We truly need more studies on this. There have been some studies in ER settings that show that there is evidence that this can be comparable to radiographs, especially in traumatic cases, but it is dependent upon the operator of the ultrasound, machine quality, and a lot of factors. Will we be using this more in the future? I guess we will see. It is an emerging diagnostic tool. It may have a wider availability, especially in rural settings. It may be more cost efficient to use, so we will see. Thank you.

3rd Edition, CASE 18

3rd Edition

Foot

ultrasound

metatarsal fractures

diagnosis

high-frequency transducer

cost-effective imaging