title: Interspinous distraction in lumbar spinal stenosis: a neurophysiological perspective.
abstract: METHODS
  Prospective neurophysiological study.
  
  
  OBJECTIVE
  To identify and quantify the neurophysiological effects of interspinous distraction during spine surgery for lumbar spinal stenosis (LSS).
  
  
  BACKGROUND
  Interspinous devices have been introduced as an alternative treatment of LSS in selected patients aiming at obtaining indirect decompression. Nevertheless, there is no data on the immediate neurophysiological effect of distraction.
  
  
  METHODS
  Thirty patients with LSS undergoing decompression (14 at single level, 16 at multiple levels) were enrolled, resulting in a total of 48 levels to be analyzed. Before decompression, calibrated incremental distraction simulating interspinous device implantation of 8, 10, 12, 14, and 16 mm was performed. Intraoperative motor evoked potentials were acquired before any distraction, during distraction at each incremental value and after bilateral decompression. We evaluated relative changes of motor evoked potentials normalized to hand muscles and related them to the number of affected levels, LSS radiological severity based on the A to D grading, lordosis, and disc height.
  
  
  RESULTS
  For single-level disease, 8-mm distraction and open decompression yielded similar improvement in motor evoked potentials not only in levels with morphological grades A or B, but also in levels with morphological grades C or D (i.e., severe or extreme stenosis) (P = 0.32). In contrast, distraction superior to 8 mm was less effective (P ≤ 0.05). In multiple-level stenosis, decompression was significantly more effective than any degree of distraction (P < 0.001). No correlation of those results to disc height or lordosis was observed. Using χ trend test to analyze the effect of distraction, a linear trend favoring moderate over severe stenotic morphology was observed (P = 0.0349).
  
  
  CONCLUSIONS
  Interspinous distraction of 8 mm is sufficient to replicate electrophysiological improvements obtained during full decompression even in severe single-level stenosis but not in multilevel disease. Interspinous distraction has therefore an immediately measurable neurophysiological effect.
  
  
  METHODS
  4.
authors.affiliation: From the Departments of *Orthopedics and †Neurosurgery, Centre Hospitalier Universitaire Vaudois (CHUV), and the University of Lausanne, Lausanne Switzerland; and ‡Hirslanden Group of Hospitals, Lausanne, Switzerland.
authors.forename: Constantin
authors.initials: C
authors.lastname: Schizas
authors.forename: Etienne
authors.initials: E
authors.lastname: Pralong
authors.forename: Christopher
authors.initials: C
authors.lastname: Tzioupis
authors.forename: Gerit
authors.initials: G
authors.lastname: Kulik
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019299:Decompression, Surgical / Q000295:instrumentation / Q000379:methods*; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D064795:Intraoperative Neurophysiological Monitoring / Q000379:methods; D008159:Lumbar Vertebrae / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care / Q000379:methods; D011184:Postoperative Period; D057234:Preoperative Period; D011446:Prospective Studies; D019736:Prostheses and Implants; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D013130:Spinal Stenosis / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*