Morphological changes in the cervical intervertebral foramen dimensions with unilateral facet joint dislocation

BackgroundMany investigators have conducted studies to determine the biomechanics, causes, complications and treatment of unilateral facet joint dislocation in the cervical spine. However, there is no quantitative data available on morphological changes in the intervertebral foramen of the cervical spine following unilateral facet joint dislocation. These data are important to understand the cause of neurological compromise following unilateral facet joint dislocation.MethodsEight embalmed human cadaver cervical spine specimens ranging from level C1-T1 were used. The nerve roots of these specimens at C5-C6 level were marked by wrapping a 0.12 mm diameter wire around them. Unilateral facet dislocation at C5-C6 level was simulated by serially sectioning the corresponding ligamentous structures. A CT scan of the specimens was obtained before and after the dislocation was simulated. A sagittal plane through the centre of the pedicle and facet joint was constructed and used for measurement. The height and area of the intervertebral foramen, the facet joint space, nerve root diameter and area, and vertebral alignment both before and after dislocation were evaluated.ResultsThe intervertebral foramen area changed from 50.72 ± 0.88 mm2 to 67.82 ± 4.77 mm2 on the non-dislocated side and from 41.39 ± 1.11 mm2 to 113.77 ± 5.65 mm2 on the dislocated side. The foraminal heights changed from 9.02 ± 0.30 mm to 10.52 ± 0.50 mm on the non-dislocated side and 10.43 ± 0.50 mm to 17.04 ± 0.96 mm on the dislocated side. The facet space area in the sagittal plane changed from 6.80 ± 0.80 mm2 to 40.02 ± 1.40 mm2 on the non-dislocated side. The C-5 anterior displacement showed a great change from 0 mm to 5.40 ± 0.24 mm on the non-dislocated side and from 0 mm to 3.42 ± 0.20 mm on the dislocated side. Neither of the nerve roots on either side showed a significant change in size.ConclusionsThe lack of change in nerve root area indicates that the associated nerve injury with unilateral facet joint dislocation is probably due to distraction rather than due to direct nerve root compression.