Cervical erector spinae plane block: a cadaver study.

Background Cervical erector spinae plane (ESP) block has been described to anesthetize the brachial plexus (BP), however, the mechanism of its clinical effect remains unknown. As the prevertebral fascia encloses the phrenic nerves, BP and erector spinae muscles to form a prevertebral compartment, a local anesthetic injected in the cervical ESP could potentially spread throughout the prevertebral compartment. This study utilizes cadaveric models to evaluate the spread of ESP injections at the C6 and C7 levels to determine whether the injection can reach the BP and its surrounding structures. Methods For each of the five cadavers, an ESP injection posterior to the transverse process of C6 was performed on one side, and an ESP injection posterior to the transverse process of C7 was performed on the contralateral side. Injections were performed under ultrasound guidance and consisted of a 20 mL mixture of 18 mL water and 2 mL India ink. After cadaver dissection, craniocaudal and medial-lateral extent of the dye spread in relation to musculoskeletal anatomy as well as direct staining relevant nerves was recorded. The degree of dye staining was categorized as “deep,” “faint,” or “no.” Results A total of 10 ESP injections were performed in five cadavers. Deep staining of the BP roots of C5, C6, and C7 was noted in 100% of the samples. Caudally, variable staining of C8 (75%) and T1 (30%) roots was seen. Faintly staining at C4 root was only seen in one sample (5%). 100% of the most relevant nerves including the long thoracic, dorsal scapular, and suprascapular nerves were deeply stained. There was faintly staining of the anterior scalene muscles (35%) anterior to the BP and the rhomboid intercostal plane caudally (40%). The phrenic nerve was deeply stained in 1 injection out of 10 and faintly stained in 2 injections out of 10. Conclusions Ultrasound-guided cervical (C6 and C7) ESP injections consistently stain the roots of the BP and dorsal rami. This study supports the notion that the cervical ESP block has the potential to provide analgesia for patients undergoing shoulder and cervical spine surgeries.