title: Pathophysiological effects of lumbar instrumentation surgery on lumbosacral nerve roots in the vertebral foramen: measurement of local pressure of intervertebral foramen.
abstract: 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.
authors.affiliation: *Department of Orthopedic Surgery, Spinal Injuries Center, Iizuka, Japan; and †Department of Orthopedic Surgery, Fukuoka University, Fukuoka, Japan.
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Morishita
authors.forename: Takeshi
authors.initials: T
authors.lastname: Maeda
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Ueta
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Naito
authors.forename: Keiichiro
authors.initials: K
authors.lastname: Shiba
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws; D002404:Catheterization / Q000295:instrumentation; D057785:Catheters; D006801:Humans; D007403:Intervertebral Disc / Q000503:physiopathology / Q000601:surgery*; D007796:Laminectomy / Q000009:adverse effects / Q000295:instrumentation*; D008159:Lumbar Vertebrae / Q000503:physiopathology / Q000601:surgery*; D056888:Patient Positioning; D011187:Posture; D011312:Pressure; D011446:Prospective Studies; D013123:Spinal Fusion / Q000009:adverse effects / Q000295:instrumentation*; D013126:Spinal Nerve Roots / Q000503:physiopathology*; D013168:Spondylolisthesis / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery*; D014160:Transducers, Pressure; D016896:Treatment Outcome