Bifid median nerve cutoff

[Linh]

Dear Steve,

The median nerve has a cutoff of 0.09cm2. But if the patient has a bifid median nerve, do you add them up at the level of the lunate and still use the same cutoff to say if there is CTS?

Best regards,
Steve

[Stephen Bird]

There is published data suggesting that you can add the two areas together and ue a cut off of 11mm2 ( 0.11cm2)
But the article states it is not as good as assessment of a non bifid nerve.
In these cases I concentrate on the other components of the assessment (change in contour / step sign / fascicle oedema / crinkle cut chip sign / etc.)
Check for space occupying lesions, solar arthritis, tenosynovitis etc.

Remember when you have a bifid nerve it commonly has a persistent median artery accompanying it. (but not always). The PMA is usually between the 2 nerves or on the ulnar aspect of them. Check for PMA thrombosis as this may occur and create acute symptoms.

Steve

[Linh]

Dear Steve,

Thanks for clarifying that. The radiologist just stated the measurement in her report and let the referring hand surgeon decide.

I have seen PMA and always turn on Color as my senior had encountered thrombosis before. Such a rare occurence!

Linh

[Stephen Bird]

It is not as rare as you think,

I have seen several cases and it is usually associated with using a vibrating piece of machinery like a jack hammer etc.

Certainly worth a thought when the patient presents with really acute onset symptoms.

Steve

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