Abstract:

Objective　To observe the anatomic relationship of atlanto-axial joint with the accessory nerve and the second cervical nerve, and to observe the innervation of sternocleidomastoid and trapezius muscle, providing the anatomy basis of sternocleidomastoid and trapezius muscles’pain caused by atlanto-axial joint misalignment. 　Methods　Three adult cadaveric neck specimens(6 sides) underwent dissection. The anatomic relationship of atlas transverse process with accessory nerve and lateral atlantoaxial joint with second cervical nerve’anterior branch, the anatomy of atlanto-axial joint’extraforaminal ligament, and the innervation of sternocleidomastoid and trapezius muscle were observed. The minimum distance between atlas transverse process tip and accessory nerve was measured.    Results    (1)Sternocleidomastoid and trapezius muscles were innerved by both accessory nerve and cervical nerve (2th~4th), and accessory nerve had communicating branch with cervical nerve. (2)Accessory nerve was situated anteriorly to the transvers process of the atlas, and a close anatomic relationship between them could be observed. The minimum distance between the tip of atlas transverse process and accessory nerve was 4.84~7.60 mm (left side) and 3.22~6.80 mm(right side). (3) Extraforaminal ligament existed in the atlanto-axial joint intervertebral foramen, which was in contact with the second cervical nerve and adhered to atlas transverse process. (4)The anterior branch of second cervical nerve travelled forward in contact with lateral atlantoaxial joint.    Conclusion    Atlanto-axial joint misalignment may stimulate the accessory nerve and thesecondcervicalnerveor its anterior branch,which may cause  sternocleidomastoid,trapezius muscle tension and pain.

Key words: Atlanto-axial , joint, Accessory nerve, Cervical nerve, Sternocleidomastoid, Trapezius