title: Restoring lumbar spine stiffness using an interspinous implant in an ovine model of instability.
abstract: BACKGROUND
  The objective of this study was to determine the effect of an interspinous implant on lumbar spine stability and stiffness during dorsoventral loading.
  
  
  METHODS
  Twelve Merino lambs were mechanically tested in vivo. Oscillatory (2 Hz) loads were applied to L2 under load control while displacements were monitored. Tri-axial accelerometers further quantified adjacent L3-L4 accelerations. Dorsoventral lumbar spine stiffness and L3 and L4 dorsoventral and axial displacements were determined over six trials of 20 cycles of loading. Four conditions were examined: 1) initial intact, 2) following destabilization at L3-L4, 3) following the insertion of an InSwing(®) interspinous device at L3-L4, and 4) with the implant secured with a tension band. Comparisons were performed using a one-way ANOVA with repeated measures and post-hoc Bonferroni correction.
  
  
  RESULTS
  Compared to the intact condition, destabilization significantly decreased lumbar stiffness by 4.5% (P=.001) which was only recovered by the interspinous device with tension band. The interspinous device caused a significant 9.75% (P=.001) increase in dorsoventral stiffness from destabilization that increased 14% with the tension band added (P=.001). The tension band was responsible for decreased displacements from the intact (P=.038), instability (P=.001), and interspinous device (P=.005) conditions. Dorsoventral L3-L4 motion significantly improved with the interspinous device (P=.01) and the addition of the tension band (P=.001). No significant differences in L3-L4 intersegmental stability were noted for axial motion in the sagittal plane.
  
  
  CONCLUSIONS
  This ovine model provided objective in vivo biomechanical evidence of lumbar instability and its restoration by means of an interspinous implant during dorsoventral spinal loading.
authors.affiliation: Department of Orthopedics, Hôpitaux Iris Sud/IRIS South Teaching Hospitals, Brussels, Belgium. Electronic address: mszp@skynet.be.
authors.forename: Marek
authors.initials: M
authors.lastname: Szpalski
authors.affiliation: Department of Orthopaedic Surgery, Edith Cavell Clinic Hospital, Brussels, Belgium.
authors.forename: Robert
authors.initials: R
authors.lastname: Gunzburg
authors.affiliation: Biomechanics Laboratory, Kinesiology Program, College of Health Solutions, Arizona State University, Phoenix, AZ, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Colloca
authors.affiliation: Bone and Joint Research Center, Department of Orthopaedic Surgery, University of North Texas Health Science Center, Fort Worth, TX, USA; Department of Materials Science and Engineering, University of North Texas, Denton, TX, USA.
authors.forename: Victor
authors.initials: V
authors.lastname: Kosmopoulos
authors.affiliation: Department of Movement Sciences, University of Idaho, Moscow, ID, USA.
authors.forename: Mostafa Afifi
authors.initials: MA
authors.lastname: Hegazy
authors.affiliation: Department of Spinal Surgery, Royal Adelaide Hospital, Adelaide, Australia; Adelaide Centre for Spinal Research, SA Pathology, Adelaide, Australia; Centre for Orthopaedic and Trauma Research, University of Adelaide, Australia.
authors.forename: Brian J C
authors.initials: BJC
authors.lastname: Freeman
authors.affiliation: Department of Orthopedics, St Pierre Hospital, Brussels, Belgium.
authors.forename: Laurent
authors.initials: L
authors.lastname: Fabeck
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001696:Biomechanical Phenomena; D004195:Disease Models, Animal; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology* / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000503:physiopathology*; D009068:Movement; D019736:Prostheses and Implants; D012756:Sheep; D013168:Spondylolisthesis / Q000503:physiopathology* / Q000601:surgery*
keywords: Biomechanics; Instability; Interspinous implant; Lumbar spine; Ovine; Spondylolisthesis; Stiffness