Image Quiz

A Cervical Spine Injury Secondary to a Motor-Vehicle Accident (continued)

Answer: Type-III dens fracture with distraction.

A lateral cervical spine radiograph demonstrated a distracted dens fracture. Magnetic resonance imaging confirmed a type-III dens fracture with vertical displacement (Fig. 1). The neurological examination could not be carried out properly because of the extremity and head injuries but was thought to reveal normal findings. The patient had hemodynamic instability, and a halo vest was applied for immobilization. Despite the halo immobilization, motion at the fracture site was noted with each ventilation viewed under fluoroscopy. Progressive quadriparesis occurred during the first twenty-four hours after the injury as hypotension was managed with blood and fluid replacement and vasopressors.


Fig. 1		 Fig. 1 Sagittal T2-weighted magnetic resonance image showing gross distraction at the dens fracture with posterior soft-tissue disruption. Patient positioning resulted in the dens being distracted during this imaging study. Note also the narrow width of the spinal cord between C5 and C7 and the appearance that it is being pulled against the lamina.

For larger view, click on image

Following resuscitation, at thirty-six hours after the injury the patient underwent a posterior C1-C2 arthrodesis with sublaminar wires and iliac crest bone graft. Transarticular screw placement was attempted, but massive bleeding was encountered from a combination of the disrupted cavernous complex of veins overlying the C1-C2 facet joints and epidural bleeding; the patient was therefore maintained in the halo vest. Over the ensuing three weeks, multiple adjustments of the vest were needed to maintain the reduction.

Because of persistent vertical instability, the patient underwent C1-C2 transarticular screw fixation twenty-five days following the initial surgical attempt. A partially threaded screw was used as a lag screw to aid in the reduction. Radiographs made ten months after the injury demonstrated bridging bone from C1 to C2 and healing of the dens fracture. The patient remained an ASIA (America Spinal Injury Association) class-A, C5 tetraplegic at the latest follow-up examination.

Discussion

Type-III dens fractures are usually relatively benign injuries associated with few complications. Low nonunion rates with halo traction and/or immobilization with a vest have been reported. We reported three cases of vertically unstable type-III dens fractures for which initial treatment with a halo device was associated with problems.

A review of the cases of 102 patients with atlantoaxial dislocation, including those treated at one center and others described in the literature, revealed a 55% prevalence of subarachnoid hemorrhage at the C2 level and a 15% rate of dural laceration or brainstem injury. Our patient had ≥5 mm of vertical displacement of the dens on the initial imaging studies. The C1-C2 facet joints were distracted >5 mm.

Postmortem studies have shown dens fractures with complete disruption of the anterior atlantoaxial ligament, tectorial membrane, and facet joint capsules on both sides with the dens held loosely by the alar ligaments. These injuries appear to have been vertically unstable type-III dens fractures similar to those described in this report. The circumferential injuries noted in a distracted type-III dens fracture explain why the reductions in this study could not be held with a halo device or sublaminar wiring alone.

The halo device, despite being perhaps the best external immobilizer for cervical spine injuries, has been reported to restrict only 75% of atlantoaxial motion. Patients moving from the supine to the sitting position have been reported to experience distraction forces of up to 9 kg when wearing a halo vest and those of up to 13 kg when wearing a halo cast. Despite our limited experience, we believe that immobilization with a halo vest is inadequate treatment for a vertically unstable dens fracture.

We believe that type-III dens fractures with >5 mm of vertical distraction are unstable and must be recognized and stabilized operatively as soon as the patient's condition allows. We recommend reduction and surgical stabilization with C1-C2 transarticular screws and posterior arthrodesis for the treatment of these fractures. A type-III dens fracture associated with distraction of the atlantoaxial facet joints, craniocervical sub-arachnoid hemorrhage, or cranial nerve palsies should suggest the possibility of vertical instability.

Reference

1. Kirkpatrick JS, Sheils T, Theiss SM. Type-III dens fracture with distraction: an unstable injury. A report of three cases. J Bone Joint Surg Am. 2004;86:2514-8.