The musculocutaneous nerve: ultrasound appearance for peripheral nerve block

To gain complete anesthesia of the forearm, block of the musculocutaneous nerve is necessary. Variations in its course and position make localization of the musculocutaneous nerve problematic. The aim of the study is to describe the ultrasound appearance of the musculocutaneous nerve in the axilla and to suggest potential areas to target neural block.

We scanned the axillary regions of 19 volunteers and assessed the size and shape of 34 musculocutaneous nerves at entry into, exit from, and in the center of the coracobrachialis muscle. Furthermore, we measured the depth of the musculocutaneous nerve under the skin surface and its distance from the axillary artery at those 3 measurement points.

As it travels through the coracobrachialis muscle, the musculocutaneous nerve changes in shape from oval to flat-oval to triangular. During this course, the musculocutaneous nerve also separates from the axillary artery and becomes more lateral while changing its depth from the surface. The musculocutaneous nerve increases its transverse area along this nerve path. In 2 subjects, the musculocutaneous nerve could not be visualized unilaterally within the course of the coracobrachialis muscle.

Knowledge of its ultrasound appearance facilitates localization and successful block of the musculocutaneous nerve. Because the distance between the musculocutaneous nerve and brachial plexus varies, different locations of musculocutaneous nerve puncture during ultrasound-guided regional anesthesia can be chosen.