Constrictive paralysis of the posterior interosseous nerve without external compression

Four cases of constrictive neuropathy of the posterior interosseous nerve (PIN) in the absence of external compression are reported. All patients presented with a history of severe elbow pain with no apparent cause, followed by paralysis of the PIN. There were one or two well-localized constrictions on the PIN proximal to the arcade of Frohse where no obvious external compressive structure was observed. After epineurotomy with or without neurorrhaphy, three patients had a complete return of motor function within 1 year. The remaining patient required tendon transfer after resection of the abnormal segment of nerve.