Advanced compressive extension injuries of the subaxial cervical spine: do we really understand the nuances of this injury?

Background context: The Allen and Ferguson classification of cervical spine injuries is widely used. They described compressive Extension (CE) injuries as having five progressive stages. Stage 4(CE4) and 5(CE5) have been described as having a posterior vertebral arch fracture involving two motion segments accompanied by displacement (dislocation) of the vertebral body at a single level. However, in their original work, CE4 was described only as a hypothetical stage, while CE5 was found in only three patients. Beyond this, little is understood about these injuries.

Purpose: To identify characteristics of compression extension injuries with vertebral body displacement (CE4 and CE5) from a series of surgically treated subaxial cervical spine fractures. A secondary aim was to identify specific characteristics that may guide treatment or affect prognosis.

Design: Retrospective case series.

Patient sample: Twenty-four patients who underwent surgical stabilization of CE4 and CE5 cervical spine fracture-dislocations in non-ankylosed spines over a 14-year period.

Outcome measures: Radiographic categorization of CE injury type, treatment rendered, postoperative spinal alignment, presence of nonunion, loss of fixation, hardware-related and neurologic complications.

Methods: After IRB approval, patients with CE injuries were identified through billing data and radiology records at a level I trauma center between January 2005 and September 2018. Demographic data, ISS, ASA, motor score, and complications during the hospitalization were collected from the patient's EMR. CT scans were reviewed to assess fracture pattern, level, and location of the vertebral arch fracture, vertebral body displacement, spinal canal diameter and method of surgical stabilization. Injuries were classified according to the classification of Allen and Ferguson, and the AO subaxial cervical spine classification.

Results: Of 221 patients identified with CE mechanism, 24 had CE4 or CE5 injuries. High-energy mechanism occurred in 92% of the patients, with motor vehicle accidents being the most common. The average ASIA motor score was 80 preoperatively and 84 at average 398 days follow-up. All CE4 and CE5 injuries occurred at C6-C7 or C7-T1. Average anterolisthesis was 6.26 mm (SD ± 2.3 mm) for CE4 and 16.8 mm (SD ± 1.8 mm) for CE5. Average spinal canal diameter at the level of dislocation was 20 mm (SD ± 0.4 mm) for CE4 and 30.5 mm (range 29.6 - 31.4 mm) for CE5. The surgical approach was anterior in 5 patients, posterior in 12 patients, and combined in 7 patients. Four patients had single-evel fixation, all of whom had CE4 injuries, and 20 patients had fixation across two or more levels. Thirty percent of patients had complications, none of which included postoperative spinal malalignment, nonunion or hardware-related complications, or worsening of neurologic exam. Three deaths occurred in the postoperative hospitalization period (7 to 15 days).

Conclusion: CE4 and CE5 injuries represented 10% and 1% of all CE injuries in our series respectively occurring only at the C6-C7 and C7-T1 levels. Though by original description these are two-level injuries, in patients with milder posterior element injury, single level stabilization was used successfully. We have therefore proposed designating CE4 into less severe CE4a and more severe CE4b injuries. Because this fracture pattern typically results in widening of the spinal canal as the anterior displacement of the vertebral body occurs independent of the fractured posterior elements, spinal cord injuries are neither as severe nor as common as in fracture-dislocation from other mechanisms.