The first descriptions of spine disorders were recorded nearly 4000 years ago in Egypt, when patients with such afflictions were left bedridden and death was considered unavoidable. One of the first extensive series on surgery of the spine was reported by Elsberg in 1925, in which the surgical treatment of spinal cord tumors was described. Since those early reports, spine surgery has made remarkable advancements, particularly since the 1980s. As surgical techniques have matured, complex operations are being performed on spine diseases once thought incurable. Moreover, increasingly older patients with multiple comorbidities are presenting for spine procedures. Consequently, the anesthetic approach to patients scheduled for spine surgery must consider the following issues: a basic knowledge of spine anatomy and imaging modalities; an awareness of the specific spine disorder being treated and the surgical procedure planned; preoperative risk assessment and optimization; potential airway difficulties; patient positioning; anesthetic choices; intraoperative medical decision-making (blood replacement, blood salvage, hemodynamic goals, pulmonary function); postoperative airway concerns; and perioperative pain management. This chapter discusses these issues.
Anatomy
The anatomy of the spine can be divided into that pertaining to the vertebral bony column and the contents of the vertebral canal.
Vertebral Column
The vertebral column is composed of 33 vertebrae. In adult life this number is functionally reduced to 24 presacral vertebrae, the sacrum, and the coccyx. The presacral vertebrae consist of seven cervical, 12 thoracic, and five lumbar bones. The five sacral and four coccygeal vertebrae fuse early in development. The vertebral column normally exhibits four curves in the anteroposterior (AP) plane. The two forward curves, or lordoses, are in the cervical and lumbar areas, and the two posterior curves, or kyphoses, are in the thoracic and sacral areas. The combination of these curves gives the normal bony spine the characteristic S shape when viewed from the side ( Fig. 21.1 ).
Each of the individual “standard” vertebrae that make up the vertebral column is a single bony structure consisting of a large body, bilateral pedicles, bilateral lamina, bilateral transverse processes, a spinous process, and four articular processes ( Fig. 21.2 ). The two pedicles laterally, the two lamina posteriorly, and the body anteriorly together form the vertebral canal, in which lies the spinal cord. The segmental nerves exit between the vertebrae through the intervertebral foramina. The four articular processes mate with corresponding processes on the vertebrae above and below to form the facet joints. The facet joint articulations provide posterior stability, and the body articulations provide anterior and vertical stability. In addition, the facet joints provide flexion, extension, and lateral rotation of the spine.
The first two cervical vertebrae, C1 and C2, differ in structure from the standard vertebrae ( Fig. 21.3 ). C1, the atlas, is ring-shaped and wider than the other vertebrae. The superior articular surfaces are configured to articulate with the two occipital condyles located at the base of the skull on either side of the foramen magnum. The atlas is composed of anterior and posterior arches, each possessing a tubercle while sharing lateral masses. The atlas has no spinous processes or body. C2, the axis, possesses a body that projects superiorly as the dens (odontoid process) (see Fig. 21.3 ), and a short bifid spinous process. The axis has two large flat superior articular facets. The transverse ligament of the atlas holds the dens in place, preventing horizontal movement of the atlas.
The anterior longitudinal ligament and the posterior longitudinal ligament (see Fig. 21.2 ) extend from the base of the skull and atlas to the sacrum. The anterior ligament is attached to the anterior surface of the vertebrae and intervertebral disks. The posterior ligament is attached to the posterior surface of the vertebrae and the intervertebral disks and lies within the vertebral canal. These two ligaments provide extension and flexion stability to the vertebral column. The supraspinal and interspinal ligaments join the spinous processes at each level, providing additional flexion stability. The ligamentum flavum unites the vertebral laminae at each level and forms part of the posterior border of the intervertebral foramen.
The intervertebral disks are fibrocartilaginous joints composed of an interior nucleus pulposus surrounded and enclosed by a tough anulus fibrosus ( Fig. 21.4 ). Together, these two components provide a strong attachment between adjacent vertebrae but allow some movement. In addition, the disks act as very efficient shock absorbers.
