Three-dimensional measurement of the course of the radial nerve at the posterior humeral shaft: An in vivo anatomical study

Purpose: Iatrogenic radial nerve injury caused by surgical exposure of the humerus is a serious complication. We aimed to describe the course of the radial nerve at the posterior humeral shaft using a three-dimensional (3D) reconstruction technique by utilizing computed tomography (CT) images of living subjects. We hypothesized that the course of the radial nerve in the posterior aspect of the humeral shaft would be reliably established using this technique and the measurements would have satisfactory intraobserver/interobserver reliabilities. Methods: This in vivo anatomical study utilized 652 upper extremity CT angiography images from 326 patients. A 3D modeling of the humerus and radial nerve was performed. We evaluated the segment of the radial nerve that lays directly on the posterior aspect of the humeral shaft and measured its proximal point, mid, and distal points. The shortest distances from the olecranon fossa to these points were defined as R1, R2, and R3, respectively. The relationships between these parameters and humeral length (HL) and transcondylar length (TL) were evaluated, and the intraobserver/interobserver reliabilities of these parameters were measured. Results: The HL was 293.6 mm, and TL was 58.64 mm on average. The R1 measured 159.2 (range 127.1-198.2) mm, R2 was 136.6 (105.7-182.5), and R3 was 112.8 (76.8-150.0) mm on average (p< .001). The intraobserver/interobserver reliabilities ranged from 0.90 to 0.98. Conclusion: The course of the radial nerve at the posterior aspect of the humeral shaft can be reliably established using the 3D reconstruction technique, and all measurements had excellent intraobserver/interobserver reliability.