Cutaneous nerve distribution around first extensor compartment of the wrist: Clinical implications for ultrasound-guided injections.

Purpose: To evaluate the course of the cutaneous nerve regarding the first extensor compartment to determine whether the dorsal or volar approach is safer for local injection into the first extensor compartment guided by ultrasound. Methods: We dissected the radial side of the wrists from 28 cadavers (52 wrists). Four-points along the imaginary line were set: the styloid process and 1 cm, 2 cm, and 3 cm proximal to the styloid process. The numbers of superficial radial nerve (SRN) and lateral antebrachial cutaneous nerve (LACN) branches were counted, and distances from the imaginary line at these points and nerve diameters were recorded. Digital images were superimposed to observe overall distribution of cutaneous nerve. Results: There were means of 3.3 SRN and 0.9 LACN branches observed in each wrist. The mean number of both SRN and LACN branches was 2.3 on the dorsal side and 1.9 on the volar side. The superimposed images indicated that both the dorsal and volar sides comprised abundant cutaneous nerves and that their paths varied markedly between patients. However, we observed that larger nerves with meaningful diameters were more abundant on the dorsal than the volar side. Conclusion: There were similar numbers of cutaneous nerves on both the dorsal and volar sides; however, we observed greater abundance of thicker cutaneous nerves on the dorsal side, and these were closer to the reference line than on the volar side. This anatomical study suggests that the risk imposed to cutaneous nerves would therefore be reduced when injection on the volar side.