Short Axis (or SAX) of the median nerve at the medial humeral condyle: showing the nerve’s relationship to the humeral head of Pronator Teres (or PT) above the level of the elbow joint. (See Figure 4)
SAX of the median nerve at the level of the radial head: Showing nerve’s relationship as it enters the pronator teres.
SAX of the median nerve at the level of the anterior elbow crease: Showing nerve between superficial and deep heads of the pronator teres.
SAX using resisted pronation of the hand with the elbow flexed in dynamic cine imaging. This will show active compression of the nerve by the adjacent muscle (pronator teres) in the tunnel. There are techniques by which either an assistant or the sonographer will perform resistance against extension and pronation while imaging the median nerve. In the following video, an additional technique is shown using an examination table. The patient is shown forcibly extending the elbow against the table and rolling the hand forcefully while pronating against the table for resistance. This motion can also be aided by the sonographer or an assistant.
Once the median nerve progresses distally in the forearm, an impingement from the pronator tunnel to the carpal tunnel is exceedingly rare. If present, it is typically caused by a mass or direct trauma.