Median nerve flattening ratio

Last revised by Daniel J Bell on 21 Apr 2023

The median nerve flattening ratio is a parameter used for the diagnosis of carpal tunnel syndrome (usually by ultrasound). It is calculated by dividing the span of the long axis by that of the short axis of the median nerve at around the pisiform level.

A ratio of greater then 3 is often considered supportive of the diagnosis of carpal tunnel syndrome.

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