Utility of helical computed tomography in differentiating unilateral and bilateral facet dislocations

Abstract

Objective: Diagnosis of cervical facet dislocation is difficult when relying on plain radiographs alone. This study evaluates the interobserver reliability of helical computed tomography (CT) in the assessment of cervical translational injuries, correlates the radiographic diagnosis with intraoperative observation, and examines the role of neurologic injury in the evaluation and diagnosis of these injuries.

Methods: Clinical histories and radiographic studies of 10 patients with cervical facet dislocations were presented to 25 surgeons. Participants classified cases as unilateral or bilateral facet dislocations after reviewing selected axial CT slices and sagittal reconstructions. Surgeons' interpretations were compared with intraoperative diagnosis. Participants interpreted the same radiographic studies with 3 different clinical scenarios: neurologically intact, incomplete, and complete spinal cord injury. Vertebral body translation from midsagittal CT was evaluated to confirm whether all unilateral facet dislocations had <25% translation.

Results: Interrater kappa coefficient showed moderate agreement between observers in classifying injuries as unilateral or bilateral (kappa: 0.54-0.58), regardless of neurologic status. Percent agreement among observers varied from 50% to 100% for each individual case. Agreement was statistically higher for bilateral facet dislocation (85%) than for unilateral dislocations (78%), with 1 unilateral fracture showing nearly 50% translation on a midsagittal image.

Conclusions: The addition of helical CT to reconstruction enables spine surgeons to more reliably distinguish bilateral from unilateral cervical facet dislocations. Despite frequent occurrence of these injuries and presumed agreement on injury description, agreement may be improved by a more precise definition of facet dislocations and subluxations and thorough review of all imaging studies.

Figure 1. Left sagittal (a), right sagittal (b), and axial (c) CT scans of the patient in Case 1 who had a unilateral facet dislocation and a contralateral facet fracture. Percent agreement among observers was the lowest of all cases (50%), probably because of the limited number of images presented of the left C3–C4 facet on the sagittal reconstructions (a) and the involvement of the facet with a fracture (arrow, c). The facet dislocation on the right C4–C5 facet is clear on the sagittal images (b).

Figure 2. CT reconstructions of Case 10 show a dislocated facet on the left at C4–C5 (a) and a subluxation or perch of the facet on the right (b). The agreement among observers was only 58% because of the lack of clear differentiation of facet dislocation from facet subluxation. The remaining apposition of the right C4–C5 facet joint led the treating physician to classify this as a unilateral facet dislocation.