Radial tunnel syndrome. An investigation of compression neuropathy as a possible cause. Conventional electromyographic and nerve-conduction studies usually do not show abnormalities in patients who have a clinical diagnosis of radial tunnel syndrome. Therefore, posterior interosseous nerve-conduction measurements were performed during forced supination in patients who had this syndrome. Only one of sixteen patients had a major increase in latency. Our data do not support the hypothesis that the signs and symptoms in most patients who have a diagnosis of radial tunnel syndrome are caused by compression of the posterior interosseous nerve. 