Dimensional Changes of the Neuroforamen After Anterior Decompression of the Cervical Spine: An In Vitro Micro–Computed Tomography Investigation

The purpose of this preliminary, cadaveric study was to quantify the dimensional changes of the neuroforamen and area available for the cord (AAC) following implantation of various interbody devices with and without posterior longitudinal ligament (PLL) removal. Eight cervical spines (C3-T1) underwent micro-computed tomography (micro-CT) scanning of the intact spine, followed by discectomy and reconstruction at three contiguous levels (C4-C7). Under conditions of intact and resected PLL, the following interbody device configurations were evaluated: 1) parallel, 2) lordotic and 3) optimal lordotic. Neuroforaminal measurements were calculated from an oblique angle and the AAC was calculated by quantifying the empty space compared to the total space available for the cord. Posterior disc height and operative range lordosis were measured and compared between groups. Neuroforaminal height and area significantly increased for all reconstruction groups compared to intact. The increase in neuroforaminal height and area was greatest following PLL resection and placement of parallel (27.1% and 43.6%, respectively) and optimal lordotic (30.5% and 41.5%, respectively) implants. The AAC increased as a function of implant placement compared to intact and increased further following resection of the PLL (p<0.05). There were no significant differences in operative range lordosis between parallel and lordotic implants. Similar to the lumbar spine, segmental distraction via placement of an interbody device produces indirect decompression of the cervical neuroforamen. Results indicate a 34% increase in neuroforaminal area and a 51% increase in AAC is achievable with appropriately sized interbody devices and adequate distraction at the posterior aspect of the vertebral body.