Hi everybody, my name is Josh Romero from Mayo Clinic in Rochester, Minnesota. This is an ultrasound case consult for cubital tunnel syndrome. I'd like to send a warm welcome to Dr. Brendan Boettcher for his help with this case. So first, we're going to start with our choice of transducer. I typically use a mid- or high-frequency transducer, depending on the patient's body habitus. Now like for all regions, you want to have a home base. So our home base is going to be the retroepicondyle groove, as depicted in the picture in the middle. We can see the blue box is designating the orientation of the transducer. It's going to be in a transverse plane relative to the arm. We can see anteriorly, or to the left, we have the mutoepicondyle, as depicted by ME. And then posteriorly, or to the right, we have OL, which is representing the olecranon. Now in between these structures, we have the ulnar nerve. Throughout this consult, in the lower left corner, you will see a depiction highlighting the orientation of the transducer for each portion of the scan. For our initial assessment, we begin by measuring the cross-sectional area of the ulnar nerve. And we typically perform this measurement at multiple locations, similar to an inching setting found in electrodiagnostic studies. We begin by taking our initial measurement at the mid-arm, taking another measurement approximately two centimeters approximate to the mutoepicondyle, take another measurement at the retroepicondyle groove, and then take a final measurement distally past the FCU heads. Now, a meta-analysis in 2017 found that a cross-sectional area greater than or equal to 10 millimeters squared was diagnosed for tubular tunnel syndrome. In our experience, patients may have a value greater or less than this, and this may or may not represent tubular tunnel syndrome. If they have clinical symptoms plus an enlarged nerve, then we would qualify that as tubular tunnel syndrome. But if a patient has an ulnar nerve that is greater than 10 millimeters squared but does not have clinical symptoms, we call this focal nerve enlargement and do not term this tubular tunnel syndrome. Now that we've performed the cross-sectional area measurements, we turn our attention to performing a qualitative assessment for focal compression. Now, the classic definition of acute tunnel syndrome includes compression of the ulnar nerve at osmorens fascia. Now, you will see variation in the nomenclature of osmorens fascia. You will also see this referred to as osmorens ligament and cupidal tunnel retinaculum. Now, we begin our examination by scanning the ulnar nerve in the retroepicondyle groove, following it distally until we see the humeral and ulnar heads of the plexicarpi ulnaris. We will see the osmorens ligament between these two heads. In the still image in the middle, we can see the humeral and ulnar heads of the FCU with the osmorens ligament in short axis. In the still image on the right, we can see the ulnar nerve in long axis with the osmorens ligament compressing superiorly. Now, it's important to understand that we will see hypochoric enlargement proximal to the site of compression, and we may also see echo-textural changes, such as a progressive loss of a normal fascicular pattern. We must also understand that the ulnar nerve can be compressed by other structures besides osmorens ligament. It can be also compressed by an anconius epitrochlearis, an intraarticular loose body, synovial hypertrophy, as well as an intraarticular hemorrhage. Next, we perform a dynamic assessment of passive elbow flexion and extension, looking for instability of the ulnar nerve. We begin with the elbow flexed to approximately 90 degrees and passively flex the elbow. In this clip, we are looking for a frankness location of the ulnar nerve over the medial epicondyle. We are seeing protruding of the ulnar nerve on the medial epicondyle, but we are not seeing frankness location. We can see mass effects from the medial head of the triceps, causing a protruding of the ulnar nerve. It is important to understand that mechanical instability of the ulnar nerve and cubital tunnel syndrome are not necessarily the same thing. This difference is important because the treatment is different if somebody is having mechanical instability of the ulnar nerve versus focal compression in what we classically think of as cubital tunnel syndrome. There are two anatomic variants we should also be aware of. The first variant is called Nanconius epitrochlearis, as well as the distal muscle belly of the medial head of the triceps. On this slide, we have a still image to the left and a CINE to the right. In the still image to the left, we have the medial epicondyle outlined anteriorly, the ulnar nerve outlined in green, the laceron outlined posteriorly, and then superior and adjacent to the ulnar nerve, we have an example of Nanconius epitrochlearis. As we play the CINE, you will see the medial epicondyle in the center of the screen, and then posterior to the right of this, we will see the ulnar nerve, as well as the Nanconius epitrochlearis, perching on the medial epicondyle. You can see the Nanconius epitrochlearis causing mass effect on the ulnar nerve. Additionally, you can see the medial head of the triceps causing mass effect. Now, getting back to our case. We have a 42-year-old gentleman with right-hand weakness, numbness, and tingling to the fourth and fifth digits in his hand. We perform a diagnostic ultrasound, and we find that he has a cross-sectional area of 14.266 millimeters squared, which we know is above the cutoff that we previously discussed. We also perform a dynamic assessment with passive elbow flexion, looking for mechanical instability of the ulnar nerve. As we perform this, we can see, in this example, perching of the ulnar nerve, but again, we're not seeing frank dislocation that would suggest instability of the ulnar nerve. The constellation of his presenting symptoms, plus this enlarged cross-sectional area measurement, and no mechanical instability of the ulnar nerve, is suggestive of cubital tunnel syndrome. For more information, visit www.FEMA.gov

3rd Edition, CASE 14

3rd Edition

Elbow and Forearm

cubital tunnel syndrome

ultrasound diagnosis

ulnar nerve

mechanical instability

Mayo Clinic