Entrapment of the posterior interosseous nerve by a fibrous band in the dorsal edge of the supinator muscle and erosion of a groove in the proximal radius.

An unusual case of transient, reversible entrapment of the PIN has been described. The entrapment was due to a fibrous band at the distal edge of the body of the supinator muscle, not at the level of the arcade of Frohse. The transient paralysis was exacerbated by pronation and alleviated by supination. Release at operation alleviated all symptoms. A radiograph showed erosion in the proximal radius, presumably due to the posterior interosseous nerve. One must consider such an entrapment of the PIN when there is weakness of muscles innervated by the radial nerve distal to its course through the supinator muscle.