지금 바로 구현할 수 있는 초급 MSK POCUS 스캔: 신경, 발목 및 골절(3부 시리즈 중 3부)

Introduction

This is the last post of this beginner series. 

We are covering some smaller structures that require a bit more skill and experience but are still doable with just a bit of practice for some very useful diagnostic information. 

Of course, I am focusing on very specific clinical questions for one specific structure, like is the median nerve swollen at the carpal tunnel. With more experience and training you may be able to answer what else is going on in the wrist.

MSK Ultrasound for Beginners (Part 3)

In this article we are checking 2 relatively small structures, the median nerve and the ATFL, plus a general strategy for evaluating for any fracture. 

In the sample scans below I am again using the 결과 D3Ultra which is adequate to answer our main clinical questions and just a fraction of the cost of a laptop or cart based unit.

Make sure the focus points are close to your point of interest. Turn up gain for a brighter image. Turn off compound imaging to get a better frame rate or turn it on for better looking pictures. Remember you can always use split screen to compare sides and as you improve your skills and experience you can add structures and answer more clinical questions.

1. Anterior Wrist to Evaluate the Median Nerve at the Carpal Tunnel

There is just one view, the short axis view, which is most useful. 

In general, you want to image pathology in two planes but for very small structures sometimes all the diagnostic information is in one plane. Once you identify the median nerve you can measure its cross-sectional area and if it is enlarged >9mm² then it is likely carpal tunnel syndrome – peripheral median nerve entrapment at the carpal tunnel. The larger it is, the more sure you can be. Virtually 100% if greater than 12mm. 

There are 2 other factors you can check for:

The mobility of the nerve, it is normal for it to ‘wiggle’ as the patient moves their fingers, so if the wiggling is absent it suggests pathology. 

The next is that nerves typically only get smaller as you go more peripheral. You can go 10cm or more proximal and see if the nerve there is larger or smaller. If the median nerve is noticeably larger at the carpal tunnel compared to the forearm that strongly suggests carpal tunnel syndrome. Some use a ratio >1.4 times larger.

The median nerve is often easier to identify when it is enlarged and hypoechoic. It can be difficult to identify since nerves and tendons can look similar in short axis. The median nerve is less sensitive to anisotropy and when the tendons are at their brightest the nerve will be slightly darker. So my first strategy to find the nerve is to tilt the transducer back and forth and the appearance of the median nerve normally stands out. 

Watch out for a normal variant, the bifid median nerve.

The image above is actually of a sort-of bifid median nerve so the median nerve is particularly flat as both parts sit next to each other. 

The second trick to finding the median nerve is to go all the way to the forearm. In the forearm the tendons turn to muscle so identifying the nerve becomes easier and then you can just follow it to the wrist to take your measurement.

I argue that ultrasound is the BEST way to evaluate for carpal tunnel syndrome, easier to perform and comparable to nerve conduction studies. ¹

In practice, I found a lot of people diagnosed with carpal tunnel based on clinical symptoms only and once imaged the median nerves were fine. The problem is often the pronator teres. If it is just pain then often myofascial trigger points in the flexors or pronator teres which can be treated via ischemic compression for a quick confirmation, “Does pressing here send pain to your hand. Is it the same as the pain you normally experience? Is the pain going down as I maintain constant pressure (for at least 20s)”. If it is just numbness or just numbness and tingling, I teach them a stretch of the pronator teres. 

Prescribing daily self-stretches have saved/cured dozens of office workers I met while working in the Cayman islands who had multiple years of carpal tunnel syndrome symptoms. In general, roughly 70% of people who told me they had carpal tunnel actually had carpal tunnel when I imaged their wrist. You can’t manage patients properly unless you have the right diagnosis so I’m thankful for learning and implementing ultrasound. I’m sure all the patients I’ve helped over the years appreciate it too.

Even if they do have carpal tunnel syndrome, consider “double crush” syndrome, where the nerve is being impinged or irritated at multiple locations: cervical spine, scalenes, clavicle, pec minor, pronator teres, and the carpal tunnel.

The full scan, with the anisotropy manoeuvre, the on-device measurement tools and the published cut-offs it is read against, is walked through frame by frame in Carpal Tunnel Ultrasound: Measuring the Median Nerve in Five Minutes.

2. Lateral Ankle for an Inversion Ankle Sprain

The most commonly injured structure in the lateral ankle with an inversion sprain is the Anterior Talofibular ligament (ATFL). When more experience and confidence is developed you should definitely add on the calcaneofibular (CFL) and anterior inferior tibiofibular ligament (AITFL – high ankle sprain).² For now lets just start with the ATFL.

In the above image pay attention to the position of the probe. 

The ligament heads from the lateral malleolus towards the medial foot, approximately at the base of the big toe. 

Many believe the fibers head straight sagittally and if you look there you are going to miss the ATFL.

We evaluate it in short axis. Increased laxity or odd echogenicity suggests pathology. Visible cortex with shadowing where it shouldn’t be suggests an avulsion sprain. If you see complete discontinuity of fibers or you move the ankle to tense the ligament while imaging and you see that the fibers don’t become taut, that suggests a full rupture.

3. Fractures (Wherever You Suspect a Fracture)

When people think of fractures, people think bones, so they think x-rays, so plain radiographs or CT. Obviously CT is best, but ultrasound is actually better than radiographs! 

But there is a catch to that. 

It is still recommended to radiograph patients if you suspect a fracture and then if negative and you still think there is a fracture to go in with your ultrasound to confirm that there is no fracture. 

Radiographs give you a chance to find fractures anywhere and everywhere, but they can be hard to read because there is so much information and fractures can easily hide, particularly non-displaced fractures. 

Ultrasound can very easily see the cortex. Any discontinuity in the cortex is pretty obvious. On top of that, ultrasound can see soft tissue so you can see the hematoma lifting the periosteum near the fracture. 

The downside is you have to slowly screen through the bone surface, and you can’t take the person’s bone out of their body to easily go all the way around. 

So ultrasound is amazing at diagnosing fractures but limited by time, patience, and angles of access to the bone.

You do have to watch out for osteophytes, erosions, or pseudo-erosions. Beginners may benefit from split screen and comparing with a healthy rib/finger or the asymptomatic side.

Catch Up on the Full Beginnier MSK POCUS Series

This is Part 3 of our beginner-friendly MSK POCUS guide. To build a comprehensive diagnostic skillset, don’t miss the rest of our MSK POCUS series designed for primary care:

• Part 1: Shoulder, Knee, and Foot Protocols
• Part 2: Elbow and Achilles Tendon Techniques
• Part 3: Nerve, Ankle, & Fracture Scans (You are here)

Conclusion:

I hope you enjoyed this introductory series to MSK ultrasound. I really hope you start or encourage colleagues to start. The worst thing that can happen is you waste 3 minutes of the patient’s and your time and the possible benefit is saving a referral, saving the patient time and money, saving having the patient to come back after imaging, being able to start proper patient management immediately, and in some cases you might even catch an occult fracture. I do offer a robust educational program if you are interested in more training.

참조

1. Fowler JR, Gaughan JP, Ilyas AM. The sensitivity and specificity of ultrasound for the diagnosis of carpal tunnel syndrome: a meta-analysis. Clin Orthop Relat Res. 2011 Apr;469(4):1089-94. doi: 10.1007/s11999-010-1637-5. Epub 2010 Oct 21. PMID: 20963527; PMCID: PMC3048245.
2. De Maeseneer M, Marcelis S, Jager T, Shahabpour M, Van Roy P, Weaver J, Jacobson JA: Sonography of the normal ankle: a target approach using skeletal reference points. AJR Am J Roentgenol. 2009, 192:487-95. 10.2214/AJR.08.1316
3. Ramakko B. The Role of Handheld Point-of-Care Musculoskeletal Ultrasound in Identifying Bone Injury: A Multi-Case Report. JIANM. 2024;21(1):2-9.