title: The impact of bone mineral density and disc degeneration on shear strength and stiffness of the lumbar spine following laminectomy.
abstract: OBJECTIVE
  Laminectomy is a standard surgical procedure for elderly patients with symptomatic degenerative lumbar stenosis. The procedure aims at decompression of the affected nerves, but it also causes a reduction of spinal shear strength and shear stiffness. The magnitude of this reduction and the influence of bone mineral density (BMD) and disc degeneration are unknown. We studied the influence of laminectomy, BMD, and disc degeneration on shear force to failure (SFF) and shear stiffness (SS).
  
  
  METHODS
  Ten human cadaveric lumbar spines were obtained (mean age 72.1 years, range 53-89 years). Laminectomy was performed either on L2 or L4, equally divided within the group of ten spines. BMD was assessed by dual X-ray absorptiometry (DXA). Low BMD was defined as a BMD value below the median. Intervertebral discs were assessed for degeneration by MRI (Pfirrmann) and scaled in mild and severe degeneration groups. Motion segments L2-L3 and L4-L5 were isolated from each spine. SFF and SS were measured, while loading simultaneously with 1,600 N axial compression.
  
  
  RESULTS
  Low BMD had a significant negative effect on SFF. In addition, a significant interaction between low BMD and laminectomy was found. In the high BMD group, SFF was 2,482 N (range 1,678-3,284) and decreased to 1,371 N (range 940-1,886) after laminectomy. In the low BMD group, SFF was 1,339 N (range 909-1,628) and decreased to 761 N (range 561-1,221). Disc degeneration did not affect SFF, nor did it interact with laminectomy. Neither low BMD nor the interaction of low BMD and laminectomy did affect SS. Degeneration and its interaction with laminectomy did not significantly affect SS.
  
  
  CONCLUSIONS
  In conclusion, low BMD significantly decreased SFF before and after lumbar laminectomy. Therefore, DXA assessment may be an important asset to preoperative screening. Lumbar disc degeneration did not affect shear properties of lumbar segments before or after laminectomy.
authors.affiliation: Department of Orthopedic Surgery, Research Institute MOVE, VU University Medical Center, De Boelelaan 1117, P.O. Box 7057, 1081 HV, Amsterdam, The Netherlands.
authors.forename: Arno
authors.initials: A
authors.lastname: Bisschop
authors.forename: Margriet G
authors.initials: MG
authors.lastname: Mullender
authors.forename: Idsart
authors.initials: I
authors.lastname: Kingma
authors.forename: Timothy U
authors.initials: TU
authors.lastname: Jiya
authors.forename: Albert J
authors.initials: AJ
authors.lastname: van der Veen
authors.forename: Jan C
authors.initials: JC
authors.lastname: Roos
authors.forename: Jaap H
authors.initials: JH
authors.lastname: van Dieën
authors.forename: Barend J
authors.initials: BJ
authors.lastname: van Royen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density / Q000502:physiology*; D002102:Cadaver; D005260:Female; D006801:Humans; D055959:Intervertebral Disc Degeneration / Q000503:physiopathology* / Q000601:surgery; D007796:Laminectomy / Q000009:adverse effects*; D008159:Lumbar Vertebrae / Q000502:physiology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000503:physiopathology*; D033081:Shear Strength / Q000502:physiology*