A Randomized Controlled Clinical Trial of Ultrasound-guided Superficial Cervical Plexus Block Positioned by the Great Auricular Nerve or Conventional Landmark Technique

Ultrasound guidance has become a reliable adjunct for brachial plexus, femoral, and sciatic nerve blocks. Furthermore, US can also be used to anesthetize purely sensory nerves such as the lateral femoral cutaneous and saphenous nerves. The superficial cervical plexus (SCP), a sensory neural plexus, supplies the skin overlying the ear, neck, angle of the mandible, shoulder, and clavicle. Traditionally, the SCP is blocked using a subcutaneous infiltration of local anesthetics along the posterior border of the sternocleidomastoid muscle. Unlike brachial plexus, sciatic nerve, etc., the SCP often cannot be displayed directly under ultrasound. The purpose of ultrasound guidance was to inject the local anesthetic solution into the correct intermuscular plane between the sternocleidomastoid and scalene muscles. In previous studies, the midpoint of the posterior border of the sternocleidomastoid muscle was often selected as the puncture point. Studies of ultrasound-guided superficial cervical plexus block are mostly unsatisfactory. Ultrasound guidance does not increase the success rate of SCP block compared with traditional technique.

The conventional landmark ultrasound guidance technique (LM group) selects the midpoint of the posterior border of the sternocleidomastoid muscle as the puncture point, but the anatomical difference of the individual cannot be considered. It may be the reason why ultrasound guidance cannot improve the success rate of the SCP block.

The great auricular nerve is the largest branch of the SCP and can be identified under ultrasound. This study intends to indirectly locate the SCP by ultrasound scanning of the point where the great auricular nerve emerges the posterior border of the sternocleidomastoid muscle (GAN Point). The method of precise SCP block at GAN Point under ultrasound guidance (GAN Group) was explored and compared with the LM Group.