Ulnar nerve compression

[David Smith]

Hi Stephen,
I’ve watched your videos discussing the “pacman” phenomenon with the ulnar nerve sometimes getting compressed as it passes the edge of the Osborne Ligament. But when I scan the elbow, I have been struggling to understand exactly where the free edge of the Osborne’s Ligament actually is with relation to the medial epicondyle, olecranon, etc. Is it possible to see some US images with all of the anatomy labeled? When you scan the ulnar nerve looking for this with the elbow flexed, do you scan the ulnar nerve in SAX along it’s path, and do you keep the elbow flexed or do you have to watch the nerve as the arm is placed into and out of flexion?
Thanks,
Dave

[Stephen Bird]

Hi Dave,

I have attached a couple of images,

The ligament is a variable feature present in some people and absent in others,

It passes from the medial epicondyle to the olecranon,

I don’t actively go looking for it with my imaging as I really don’t care if it is present, thin, thick, absent etc.

What I do care about is extrinsic compression of the ulnar nerve with elbow flexion,

So I scan the ulnar nerve in short axis with the elbow extended. I do this with the patient supine and the arm raised above their head resting on a second pillow so it is comfortable for the shoulder.

I scan in short axis from the mid humeral level down to the mid forearm as this covers the Struthers canal area and the cubital tunnel comprehensively.

Then I ask the patient to place their hand in front of their chin as this creates elbow flexion.

Then I repeat the short axis assessment.

You may then notice a paceman extrinsic compression when in flexion. This nearly always correlates to the area of neural oedema you have noticed in extension.

A key point is normal volunteers often create the paceman sign extrinsic compression and this is OK. If someone has a thick Osborne ligament and compresses the nerve with flexion this may remain asymptomatic if the patient does not often perform elbow flexion.

We see this all the time with ultrasound. One person with a prominant Steida process of the talus for example may be asymptomatic, but another will have severe posterior ankle impingement problems. The first patient is an accountant and the second is a ballerina.

So a thick ligament is a risk factor and then if you have many elbow flexions in your work or recreation you have many compression events until eventually you develop neural oedema and symptoms.

Don’t get obsessed with identifying the ligament, simply look in the short axis for the compression when in flexion. When you see the extrinsic compression you will notice the ligament.

It is all done in the short axis of the nerve and you don’t need to scan the nerve while the flexion is being performed. This is essential when looking for subluxation, however this more common extrinsic compression is different.

I think it is a common cause of ulnar nerve cubital tunnel irritation.

Finally I do like to check the length of the nerve from the armpit to the hand. Short axis it is a quick process and makes sure i don’t miss something like a nerve sheath tumour in a random location,

Steve.

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[David Smith]

Excellent. Thanks Steve. That clears it up. Cheers, Dave

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