A new clinical test for radial tunnel syndrome--the Rule-of-Nine test: a cadaveric study.

PURPOSE Radial tunnel syndrome refers to pain on the lateral aspect of the forearm as a result of compression of the posterior interosseous nerve within a tunnel with specific anatomical boundaries. Diagnosis of the condition is difficult because of its close association with lateral epicondylitis, which warrants different methods of treatment. Based on a cadaveric study, a new clinical test, the Rule-of-Nine test, is proposed to improve the diagnostic accuracy in radial tunnel syndrome. The test involves constructing 9 equal squares on the anterior aspect of the forearm and noting those squares where tenderness can be elicited. METHODS 19 upper limbs were dissected to delineate the path of the posterior interosseous nerve through the radial tunnel, and the relationship of the path of the nerve with the 9 squares. RESULTS A consistent mapping of the posterior interosseous nerve to the lateral column of 3 squares was observed. CONCLUSION The Rule-of-Nine test is proposed as a reliable method of diagnosing radial tunnel syndrome.