[Electroneuromyographic study of the radial nerve at the brachium level: standard values and conduction block].

A study aims to design an electroneuromyographic technique of radial nerve investigation and conduction block (CB) definition at the spiral groove level using surface electrodes. Eight healthy volunteers, 17 patients with focal radial nerve neuropathy in the spiral groove, 4 patients with a complete injury of the radial nerve aged from 22 to 54 years have been studied. The M-response was recorded from the extensor digitorum communis. Stimulation was performed at (1) the lateral brachium; (2) the Erb's point; (3) the medical brachium (stimulation of the median and ulnar nerves). Normal values have been determined. CB was calculated as follows: 100-A2/(A1+A3)*100%, where A1--a value of the M-response area amplitude at first point stimulation, A2--the second one, A3--the third one. The proximal M-response is the sum of motor unit action potentials of posterior and anterior groups of forearm muscles. Proximal M-response in patients with a complete injury of the radial nerve did not differ from the third one. The correlation between CB and the paresis degree as well as surface EMG were revealed in patients with radial neuropathy. Besides, there was correlation between CB and the percentage contribution of the third M-response in proximal one in this group.