We treated 31 patients with non-traumatic paralysis of the posterior interosseous nerve over 15 years. There were 10 men and 21 women of mean age 40.3 years (17 to 71). Six were managed conservatively, and 25 by operation.

In 14 patients entrapment occurred at the supinator, including three who had double compression at both the entrance and exit from the muscle. In four it was caused by a ganglion, in one by a lipoma, in one by a dislocated radial head and in two by a marked constriction in the nerve of unknown cause. The remaining three patients were retrospectively diagnosed as having neuralgic amyotrophy, the only observable change at operation being slight oedema of the nerve.

Paralysis recovered in 24 out of the 25 patients at between 2 to 18 months (mean 5.6) after operation, and the one failure was treated later by tendon transfer.