title: Minimally invasive intraoperative stiffness measurement of lumbar spinal motion segments.
abstract: OBJECTIVE
  To test a new tiny-tipped intraoperative diagnostic tool that was designed to provide the surgeon with reliable stiffness data on the motion segment during microdiscectomy. A decrease in stiffness after nuclectomy and a measurable influence of muscle tension were assumed. If the influence of muscle tension on the motion segment could at least be ruled out, there should be no difference with regard to stiffness between women and men. If these criteria are met, this new intraoperative diagnostic tool could be used in further studies for objective decision-making regarding additional stabilization systems after microdiscectomy.
  
  
  METHODS
  After evaluation of the influence of muscle relaxation during in vivo measurements with a spinal spreader between the spinous processes, 21 motion segments were investigated in 21 patients. Using a standardized protocol, including quantified muscle relaxation, spinal stiffness was measured before laminotomy and after nuclectomy.
  
  
  RESULTS
  The decrease in stiffness after microdiscectomy was highly significant. There were no statistically significant differences between men and women. The average stiffness value before discectomy was 33.7 N/mm, and it decreased to 25.6 N/mm after discectomy. The average decrease in stiffness was 8.1 N/mm (24%).
  
  
  CONCLUSIONS
  In the moderately degenerated spine, stiffness decreases significantly after microdiscectomy. Control for muscle relaxation is essential when measuring in vivo spinal stiffness. The new spinal spreader was found to provide reliable data. This spreader could be used in further studies for objective decision-making about additional stabilization systems after microdiscectomy.
authors.affiliation: Department of Spine Surgery, Paracelsus Medical University Hospital, Salzburg, Austria. mkrenn@salk.at
authors.forename: Michael H
authors.initials: MH
authors.lastname: Krenn
authors.forename: Sveva
authors.initials: S
authors.lastname: Ambrosetti-Giudici
authors.forename: Alois
authors.initials: A
authors.lastname: Pfenniger
authors.forename: Jürgen
authors.initials: J
authors.lastname: Burger
authors.forename: Wolfgang Peter
authors.initials: WP
authors.lastname: Piotrowski
mesh_terms: D001696:Biomechanical Phenomena; D003949:Diagnostic Techniques, Surgical / Q000295:instrumentation*; D017587:Diskectomy, Percutaneous / Q000295:instrumentation*; D004867:Equipment Design; D005260:Female; D006801:Humans; D007405:Intervertebral Disc Displacement / Q000175:diagnosis / Q000503:physiopathology* / Q000601:surgery; D007432:Intraoperative Period; D008159:Lumbar Vertebrae / Q000503:physiopathology* / Q000601:surgery; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D019060:Minimally Invasive Surgical Procedures / Q000295:instrumentation*; D009126:Muscle Relaxation; D016059:Range of Motion, Articular; D017678:Sex Distribution; D013314:Stress, Mechanical; D013525:Surgical Instruments / Q000592:standards