Flexion and Extension Fractures of the Subaxial Cervical Spine

Injuries to the cervical spine are common in blunt traumatic mechanisms, occurring in up to 2-3% of all such patients.  Of these, approximately 60% of fractures and 75% of dislocations occur in the subaxial cervical spine (i.e. C3-C7). The increased motion allowance of the cervical spine puts this area at particular risk for both bony and ligamentous injury during high-impact mechanisms. However, several stabilizing elements counteract this to provide in-line stability. The anterior column contains all of the structures anterior to the cord. The anterior and posterior longitudinal ligaments (ALL/PLL) run along their respective sides of the vertebral bodies to maintain stability in the anterior-posterior direction, and the intervertebral disks maintain spacing. The posterior column includes the cervical facet joints, pedicles, laminae, and transverse and spinous processes. Posterior elements are held intact by the nuchal ligamentous complex (supra-, infra- and interspinous ligaments, ligamentum flavum). Both the anterior and posterior columns must remain intact to prevent motion of the vertebrae relative to one another and protect the integrity of the spinal canal.

Anterior wedge fractures occur with severe flexion of the spine, causing compression of the anterior portion of a vertebral body. The resultant fracture is usually evident on plain radiography and associated with loss of anterior vertebral height. Most commonly the posterior and anterior columns remain intact, and thus these are generally considered to be stable fractures. However, flexion-extension films may reveal anterolisthesis and warrant further investigation.  Instability occurs most commonly in the setting of multiple adjacent compression fractures or greater than 50% loss of anterior vertebral height.

Teardrop fractures occur with both severe flexion and extension of the cervical spine, and are classified as such. Flexion teardrop fractures occur when the anterior portion of two adjacent vertebrae collide at high impact. The fracture pattern usually consists of a smaller wedge (teardrop) fragment which displaces anteriorly, and a larger posterior component. The anterior fragment generally remains associated with the ALL, but the significant posterior force applied to the larger fragment often results in disruption of the PLL. The posterior and anterior fragments move independently of one another and can cause severe instability at this level.

Extension teardrop fractures occur, as the name would suggest, with severe extension of the neck. The fracture pattern is similar to flexion teardrops in that a smaller, anterior fragment is separated from a larger posterior component, and they may appear virtually identical on plain radiography. Loss of vertebral height is not commonly seen with extension fractures though, and may help distinguish them from flexion injuries. The extension teardrop fracture is an avulsion, with instability arising from ALL disruption rather than PLL. The anterior-inferior corner of the vertebra is avulsed from the body, and thus the anterior column is no longer intact. The most common site of the extension teardrop is actually at C2, but subaxial vertebrae are also at risk.

In order to stratify these injuries, the Subaxial Injury Classification Scale (SLIC) was developed (see below). This grading scale is used to evaluate fractures in the acute setting, in terms of both prognostic implications and decisions of operative vs. non-operative management.  It includes 3 major categories based on significant predictors of clinical outcome: bony injury morphology, integrity of the ligamentous complexes, and patient neurologic status. Points are assigned for each, and a score of 5 or greater mandates surgical intervention. Scores of 3 or less can be managed non-operatively, and a score of 4 is equivocal and should be left to the surgeon’s judgement. In a number of series, increased SLIC scores have correlated with higher rates of severe, prolonged neurologic disability as well as mortality.

Recognition of these fractures requires a working knowledge of the anatomy of the subaxial cervical spine, as well as a careful history and physical examination when available. All of these fracture patterns should be considered potentially unstable until the ligamentous elements of the spine have been appropriately evaluated, and maintenance of stabilization with a cervical collar should be mandatory until that time.

SUBAXIAL INJURY CLASSIFICATION SCALE (SLIC)

Category	Points
Morphology
No abnormality Compression ± burst Distraction Rotation or translation	0 1 ± 1 = 2 3 4
Discoligamentous Complex
Intact Indeterminate Disrupted	0 1 2
Neurologic Status
Intact Root Injury Complete cord injury Incomplete cord injury Continuous cord compression	0 1 2 3 + 1

References

1.           Dvorak MF, Fisher CG et al. The Surgical Approach to Subaxial Cervical Spine Injuries: An Evidence Based Algorithm Based on the SLIC Classification System. 2007. Spine. 32: 2620-29.

2.           Zahir U, Ludwig SC, et al. The Subaxial Cervical Spine Injury Classification System. In: Spine and Spinal Cord Trauma: Evidence-Based Management. Vaccaro A, Ed. Thieme Pulishers, 2010.

3.           Up To Date: Spinal column injuries in adults: Definitions, mechanisms, and radiographs. Accessed October 22, 2013. http://www.uptodate.com

by Dr. Jordan Stern