Triple hourglass-like fascicular constriction of the posterior interosseous nerve: a rare cause of PIN syndrome.

Supinator syndrome or posterior interosseous nerve (PIN) syndrome is a compression neuropathy of the deep branch of the radial nerve in the region of the Arcade of Frohse. An extremely rare cause of an acute onset supinator syndrome is the hourglass-like fascicular constriction of the posterior interosseous nerve due to torsion. To our knowledge, only a limited number of cases which describe the sonographic appearance of fascicular torsions are known in the literature. We present a rare case of a supinator syndrome associated with hourglass-like constrictions of the PIN diagnosed by means of sonography.