Surgical anatomy of the anterior cervical spine: the disc space, vertebral artery, and associated bony structures.

OBJECTIVE To elucidate the relationships between the neurovascular structures and surrounding bone, which are hidden from the surgeon by soft tissue, and to aid in avoiding nerve root and vertebral artery injury in anterior cervical spine surgery. METHODS Using six cadaveric spines, we measured important landmarks on the anterior surface of the spine, the bony housing protecting the neurovascular structures in the lateral disc space, and the changes that occur during the discectomy with interbody distraction of the vertebral bodies. The measurements included the distance between the medial borders of the longus colli muscle at the level of each interspace; the width and height of each disc space at the midline; the width and height of the costal process; the distances between the cranial tip of the uncinate process (UP) and the vertebral body (VB) above and from the tip of the UP to the vertebral artery; the anteroposterior diameter or the extent of the disc spaces in the midline; the height at the midpoint of the distracted disc space; the UP-VB distance in distraction; and the width of the visible nerve root. RESULTS The distance between the medial borders of the longus colli muscles increased in a rostral to caudal direction. The height of the UP was shortest at C4-C5 and greatest at C5-C6; the width was narrowest at C4-C5 and widest at C6-C7. The width of the costal process measured from the VB to the anterior tubercle was narrowest at C2-C3 and widest at C6-C7. The midpoint height of the costal process was smallest at C6-C7 and tallest at C4-C5 and C5-C6. The nondistracted UP-vertebral artery distance was the shortest at C2-C3 and longest at C4-C5. The nondistracted UP-VB distance averaged 1 mm at C2-C3 and C6-C7 and 1.5 mm at C4-C5. The height of the distracted disc space was shortest at C2-C3 and C6-C7. The UP-VB distance after distraction was greatest at C4-C5. Only at the C2-C3 interspace was the nerve always above the process. The vertebral artery entered the foramen transversarium of C6 in all the specimens. CONCLUSION Although avoiding unfortunate injury is not always possible, understanding the locations and relations among the anatomic features is the only safeguard against unwarranted damage.