title: The effects of lumbar facet dowels on joint stiffness: a biomechanical study.
abstract: BACKGROUND
  Facet joint arthrosis may play a significant role in low back pain generation. The placement of facet dowels is a percutaneous treatment that aims to fuse the facets and increase joint stiffness. In this cadaveric study, we evaluated spine stiffness after facet dowel insertion in combination with several surgical procedures and determined which motions promote dowel migration.
  
  
  METHODS
  Six fresh frozen lumbar spines were tested in flexion-extension, lateral bending, and axial rotation. Spine stiffness was determined for the intact specimens, after L4 laminectomy, and after bilateral L4-L5 facet dowel placement, respectively. One specimen underwent a unilateral transforaminal lumbar interbody fusion (TLIF) construct and another underwent extreme lateral interbody fusion (XLIF) graft (22 mm) placement, followed by placement of facet dowels. Afterwards, the specimens were subjected to 10,000 cycles of fatigue testing in flexion-extension or axial rotation.
  
  
  RESULTS
  The overall decrease in stiffness after laminectomy was 4.6%. Facet dowel placement increased overall stiffness by 7.2%. The greatest increase was seen with axial rotation (13%), compared to flexion, extension, and lateral bending (9.5%, 2.3%, and 5.6%, respectively). The TLIF and XLIF plus dowel construct increased specimen stiffness to 266% and 163% of baseline, respectively. After fatigue testing, dowel migration was detected by computed tomography in the 2 uninstrumented specimens undergoing axial rotation cycling.
  
  
  CONCLUSIONS
  Facet dowels increase the stiffness of the motion segment to which they are applied and can be used in conjunction with laminectomy procedures to increase the stiffness of the joint. However, dowel migration can occur after axial rotation movements. Hybrid TLIF or XLIF plus facet dowel constructs have significantly higher stiffness than noninstrumented ones and may prevent dowel migration.
authors.affiliation: Department of Neurosurgery, Louisiana State University Health Sciences Center, New Orleans, LA.
authors.forename: Jayme
authors.initials: J
authors.lastname: Trahan
authors.affiliation: Department of Neurosurgery, Louisiana State University Health Sciences Center, New Orleans, LA.
authors.forename: Eric
authors.initials: E
authors.lastname: Morales
authors.affiliation: Department of Neurosurgery, Louisiana State University Health Sciences Center, New Orleans, LA.
authors.forename: Erich O
authors.initials: EO
authors.lastname: Richter
authors.affiliation: Department of Neurosurgery, Louisiana State University Health Sciences Center, New Orleans, LA.
authors.forename: Gabriel C
authors.initials: GC
authors.lastname: Tender
keywords: Biomechanics; foreign-body migration; instrumentation; laminectomy; low back pain; lumbar vertebrae; surgical procedures–minimally invasive