FORAMINAL PRESSURE CHANGES DURING INTERVERTEBRAL DISTRACTION SIMULATING ANTERIOR CERVICAL DISKECTOMY

Distraction of the disc space over baseline height has been shown to i ncrease foraminal size. The purpose of this procedure is to determine pressure changes, with disc space distract:ion simulating an anterior cervical discectomy and fusion (ACDF). An analysis of pressure changes during disc space distraction at C5-C6 was performed. Data were analy zed for maximal pressure observed and for pressure change with prolong ed distraction. Five cadaveric specimens underwent a discectomy at the C5-C6 level. Distraction of the disc space was performed and pressure measurements were obtained from within the foramen. Measurements were made for maximal pressure with an intact posterior longitudinal ligam ent (PLL), divided PLL, and with the nerve root removed from within th e foramen. Pressures were also recorded with prolonged distraction unt il a steady state was achieved. Incremental distraction of +2, +4, and +6 mm resulted in pressure increases within the foramen. Sectioning o f the PLL did not affect these increases. Removal of the nerve root fr om the foramen resulted in pressure increases; however, these were not significantly different from baseline. Prolonged distraction produced an initial increase and a gradual return toward baseline. Final press ures still differed significantly from baseline. Increase intraforamin al pressures can be seen with increasing disc space distraction such a s occurs during an ACDF. This suggests that either the foramen narrows in at least one dimension and/or soft-tissue attachments to the nerve produce a tensile force in the nerve as they tighten. The pressure in creases relax over time.