Foraminal Pressure Changes During Intervertebral Distraction Simulating Anterior Cervical Discectomy

Abstract

Distraction of the disc space over baseline height has been shown to increase foraminal size. The purpose of this procedure is to determine pressure changes, with disc space distraction simulating an anterior cervical discectomy and fusion (ACDF). An analysis of pressure changes during disc space distraction at C5-C6 was performed. Data were analyzed for maximal pressure observed and for pressure change with prolonged 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 ligament (PLL), divided PLL, and with the nerve root removed from within the foramen. Pressures were also recorded with prolonged distraction until a steady state was achieved. Incremental distraction of +2, +4, and +6 mm resulted in pressure increases within the foramen. Sectioning of the PLL did not affect these increases. Removal of the nerve root from 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 pressures still differed significantly from baseline. Increase intraforaminal pressures can be seen with increasing disc space distraction such as 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 increases relax over time.