Identification of the radial nerve is important during the posterior approach to a humerus fracture. During this procedure, the patient can be placed in the prone or lateral decubitus position depending on the surgeon’s preference. The distance from the radial nerve to the osseous structures will be different in each position. The purpose of this study was to identify the safety zones of the various patient and elbow flexion positions. The distances from the olecranon to the center of the radial groove and intermuscular septum and lateral epicondyle to the lateral intermuscular septum were measured using a digital Vernier caliper. The measurements were performed with the cadavers in the lateral decubitus and prone positions with different elbow flexions. The distance from where the radial nerve crossed the posterior aspect of the humerus measured from the upper part of the olecranon to the center of the radial nerve in both positions with different elbow flexion angles varied from a mean maximum distance of 130.00 mm with the elbow in full extension in the prone position to the shortest distance of 121.01 mm with elbow flexion of 120 degree in the lateral decubitus position. The mean distance of the radial nerve from the upper olecranon to the lateral intermuscular septum varied from 107.13 mm to 102.22 mm. The distance from the lateral epicondyle to the lateral edge of the radial nerve varied from 119.92 mm to 125.38 mm. There was very little change in the measurements and no important different distances of radial nerve location until the elbow was flexed to 120 degrees, which was not significant as this flexion is rarely used.