Pathophysiological effects of lumbar instrumentation surgery on lumbosacral nerve roots in the vertebral foramen: measurement of local pressure of intervertebral foramen.

Methods: Measurement of local pressure of the intervertebral foramina. Objective: To evaluate the pathophysiological effects of lumbar instrumentation surgery on lumbosacral nerve roots in the vertebral foramen.

Background: The physiological states of lumbosacral nerve roots in the vertebral foramen remain controversial.

Methods: From 2000 to 2012, 11 of 710 patients with L4 degenerative spondylolisthesis failed to develop postoperative radiculopathy because of intraoperative pedicle screw malposition (L5: 10, L4: 1). We prospectively evaluated the local pressure at the L4-L5 and L5-LS vertebral foramina in 18 patients with L4 degenerative spondylolisthesis. All patients underwent L4-L5 posterolateral fusion (PLF) with L3-L4-L5 laminotomy. Intraoperatively, local pressure of the intervertebral foramen was measured using a catheter pressure transducer while changing the lumbar spine posture, and the measurement was performed before and after L4-L5 PLF.

Results: The local pressures at the L4-L5 vertebral foramen were 29.74 ± 16.26 and 51.57 ± 23.18 mm Hg (before fixation), and 39.13 ± 17.69 and 41.71 ± 17.94 mm Hg (after fixation) in the lumbar spine neutral and extension postures, respectively. The local pressure before fixation increased significantly during lumbar spine extension (P < 0.001), although the value after fixation was almost identical. The local pressures at the L5-LS vertebral foramen were 26.91 ± 18.16 and 54.36 ± 26.67 mm Hg (before fixation), and 24.82 ± 17.1 and 58.46 ± 32.78 mm Hg (after fixation) in the lumbar spine neutral and extension postures, respectively. The local pressure before and after fixation increased significantly during lumbar spine extension (P < 0.001), and the values after fixation were higher than those before fixation.

Conclusions: The local pressure at the L4-L5 vertebral foramen did not change during lumbar extension after L4-L5 PLF, whereas the local pressure at the L5-LS vertebral foramen was significantly increased during lumbar extension after L4-L5 PLF. Our results suggested that the nerve roots caudal to the fixed segments may be exposed to higher external dynamic stresses after lumbar instrumentation surgery. Methods: 4.