Surface projection of the radial tunnel under the supinator muscle: A cadaver study

The purpose of the study was to develop a method for locating surface projections of structures related to the radial tunnel using thumb interphalangeal joint (IPJ) coefficients. Distances from vertical and transverse planes through the lateral epicondyle of the humerus to entry (arcade of Frohse AF) and exit points of the deep branch of the radial nerve (DBRN) from the supinator muscle were measured on nine cadavers. Average distances were used to find coefficients in terms of IPJ widths. The accuracy of using these coefficients in locating the AF was tested by ink injection on five other cadavers. The average IPJ width from these cadaver upper extremities and from an additional sample of 43 healthy adults was approximately 2.0 cm. The mean transverse plane to entry and exit point distances were 4.2 cm (∼2 IPJ widths) and 7.6 cm (∼3.8 IPJ widths) respectively. The mean vertical plane to entry and exit point distances were 1.9 cm (∼1 IPJ width) and 1.0 cm (∼0.5 IPJ width) respectively. Mean radial tunnel length under the supinator was 3.1 cm (∼1.5 IPJ widths). This study presents a method for identifying approximate locations of structures related to the radial tunnel that may aid clinicians in examination and treatment of radial tunnel syndrome.