Postoperative Spinal Disorders—Cervical

Background

In this chapter, we will explore the biomechanical and surgical factors that lead to iatrogenic destabilization of the cervical spine, along with providing a detailed understanding and discussion of risk factors for specific postoperative disorders that can occur following these operations. The spine is often divided into three columns for biomechanical discussion, with the anterior column consisting of the anterior longitudinal ligament (ALL) and anterior half of the vertebral body and annulus fibrosus, the middle column consisting of the posterior half of the vertebral body and annulus fibrosus and posterior longitudinal ligament (PLL), and the posterior column consisting of the facet joints, laminae, and ligaments dorsal to the spinal cord. Denis first reported this classification, hypothesizing that significant instability could result from disruption of at least two of these columns and noting that the middle column was the most important contributor to stability. ^, Although the Denis classification is the simplest classification system for describing spinal instability, its practical utilization has been questioned, and many other classification systems have been proposed. Although bony disruption can be seen readily on radiographs and computed tomography (CT) scans, ligamentous disruption is most readily assessed via magnetic resonance imaging. Therefore, surgeons should take a broad diagnostic approach to ascertaining the specific cause of cervical spine iatrogenic instability.

Anterior Cervical Spine Surgery

Anterior Surgery Biomechanics

Anterior spinal surgery can directly disrupt the ALL, PLL, annulus fibrosus, and vertebral bodies. The ALL is stronger than the PLL and contributes to the prevention of overextension injuries to the spine; thus, disrupting this key tension-holding ligament can lead to significant instability with forces extending the spine. Furthermore, during anterior corpectomy for dural sac decompression both the ALL and PLL may be disrupted, and further instability can ensue from the accompanying vertebral body resection. Benzel devised a system that divides the vertebral body into 27 equally-sized cubes to describe the potential for instability after surgery ( Fig. 56.1A and B ). Because the strongest forces on the spine occur during flexion, and the anterior cubes are furthest from the axis of rotation, resection of the vertically-oriented anterior set of cubes will lead to more instability than corresponding resection of the middle or posterior set of cubes (see Fig. 56.1C–F ). Similarly, destruction of the horizontally-oriented middle set of cubes will lead to more instability than either the top or bottom sets, with possible ensuing vertebral body collapse into the vacated space (see Fig. 56.1G–H ). To stabilize the spine following corpectomy or significant decompression through annulus fibrosus removal, interbody cages and struts, respectively, can be used to properly stabilize the spinal column. Oblique cervical corpectomy can also provide spinal canal decompression without complete destabilization of the spine ( Fig. 56.2 ).