Identifying safety zone of invasive procedures in the sternocleidomastoid muscle using ultrasonography

Dysfunctions of the sternocleidomastoid (SCM) muscle, such as myofascial syndrome, torticollis, and cervical dystonia, have been treated using several invasive procedures. In such situations, it is possible to injure the adjacent nerves. This study aimed to demonstrate the course of these nerves in healthy volunteers using ultrasound. The great auricular nerve (GAN), spinal accessory nerve (SAN), transverse cervical nerve (TCN), and supraclavicular nerve (SCN) were scanned by ultrasonography in 26 healthy volunteers. The neck was scanned in the supine position with the head turned 45° to the contralateral side. The cervical plexus was detected in half of the SCM muscle. Each nerve was then traced to the level of contact with the anterior border of the SCM muscle. The following features of the nerves were recorded bilaterally: vertical and horizontal positions of each nerve at the posterior border of the SCM and the cross-sectional area and depth of each nerve at the reference line and anterior border of the SCM. The mean proportions of GAN, SAN, TCN, and SCN were 26%, 26%, 48%, and 80%, respectively near the posterior border, whereas they were 18%, 23%, and 51% for GAN, SAN, and TCN, respectively, at the level of the reference line. Notably, SCN was not visible at the level of the reference line. The mean TCN proportion was 47% at the anterior border of the SCM. The precise location of the nerves and their relationship with the SCM muscle should be considered during invasive procedures. It is recommended that the procedure be performed in the lower half of the SCM muscle, which refers to 50 to 80% of the proportions in our study.