Submitted by Rocio Carolina Garcia Santibanez, MD, News Science Editorial Board
Park HJ, Yoon JS, Rhee WI, Kim JW, Yang SN, Won SJ. Effect of fascia penetration on sensory nerve conduction in the superficial radial nerve.
J Clin Neurophysiol. 2018 Feb 12. doi:10.1097/WNP.0000000000000461. [Epub ahead of print] PubMed PMID: 29438175.
In this study, the investigators sought to determine the effect of the fascia penetration of the radial nerve in its sensory nerve action potential amplitude. After its origin, the superficial radial nerve courses under the brachioradialis muscle and around the distal to mid-forearm, it pierces the fascia of the muscle and runs in the subcutaneous tissue. The investigators used ultrasound to localize the point of penetration (PP) of the fascia in 83 healthy subjects. The mean PP distance from the styloid process was 8.3 cm (range 5-13). In 20% the PP was less than 7 cms from the styloid process. Nerve conduction studies of the superficial radial nerve were obtained in 25 healthy volunteers with supramaximal stimulation at 5 points (at the PP, 2 and 4 cm proximal to the PP, 2 and 4 cm distal to the PP). The highest amplitude was 2 cm distal to the PP (mean 50.1 mv). The lowest were 2 and 4 cm proximal to the PP (mean 38.1 and 29.7).
This study highlights the importance of being familiar with the anatomy of commonly tested peripheral nerves. The standard 10 cm distance for stimulation aligns closely with the 2 cm distal to PP point as there are approximately 3 cms between the styloid process and the recording electrode. Because 20% of patients can have the PP at less than 7 cms from the styloid process, it is reasonable to stimulate more distally if the amplitude appears small. It remains unclear if there is any utility of ultrasound for obtaining the largest possible amplitude.