A case of rotational restriction of the forearm due to abnormal configuration of pronator quadratus muscle.

We present a case of rotational restriction of the forearm due to abnormal configuration of the pronator quadratus muscle. A 20-year-old man developed right wrist joint pain on pitching of a baseball game and thereafter displayed rotational disorder of the forearm. Magnetic resonance imaging (MRI) revealed a space-occupying lesion from the volar side of the radius to the dorsal side of the ulna.