Quantitative Analysis of the Radial Nerve Pathway Relative to the Humerus Shaft Length: A Cadaveric Study Aimed at...

The aim of this study was to provide a detailed anatomical mapping of the radial nerve's course relative to the humerus and to propose a length-normalized, ratio-based posterior "safe zone" for dual plate fixation in distal shaft fractures to reduce the risk of iatrogenic radial nerve injury.

We dissected 42 upper arms from 21 embalmed adult cadavers (mean age, 74.1 years) and measured the radial nerve in relation to key humeral landmarks from the posterior aspect. Two orthopedic surgeons performed 2 trials each, and intra- and interobserver reliability were high with Cronbach's alpha values of 0.813 and 0.910, respectively. A posterior safe zone for dual plate fixation using an 8-hole 3.5 locking compression plate (LCP) medially and a 7-hole LCP laterally with at least 2 screws per side was defined by expressing fracture location as proportions of humeral length relative to established landmarks.

The radial nerve entered the medial humerus at 40.5% and exited laterally at 57.0% of humeral length measured from the proximal end. Key absolute measurements were as follows: proximal humerus to the upper margin of the radial groove, 101.4 mm (range, 58-134 mm); groove length, 43.8 mm (range, 14-72 mm); upper margin of the groove to the olecranon fossa, 127.3 mm (range, 118-159 mm). Expressed as proportions, the posterior safe zone for dual plating spanned 49.1%-76.8% on the posteromedial aspect and 65.5%-88.9% on the posterolateral aspect of the proximal-to-lateral-epicondyle distance, corresponding to 115.3-180.4 mm and 153.7-208.8 mm, respectively, based on the mean humeral length.

This cadaveric study proposes a length-normalized posterior safe zone for dual plating in distal humerus fractures. These anatomical guidelines may assist preoperative planning to avoid radial nerve injury, but clinical validation is required.