Impact of intervertebral graft height on biomechanical stability of cervical vertebrae，an experimental study

English Keywords:Cervical  Intervertebral height  Graft  Biomechanics

English Abstract:

  【Abstract】 Objective：To study the impact of intervertebral graft height on immediate biomechanical stability of lower cervical spine after Smith-Robinson discectomy and determine the optimal graft height.Method：Six fresh-frozen human cadaveric cervical spines were used in this series，tricortical graft from iliac crest bone were harvested，and specimens were tested in five conditions，normal（specimens with intact discs） and different graft height（120%，140%，160% of baseline height） after Smith-Robinson discectomy.Each specimens were subjected to flexion-extension，lateral bending and axial rotation in material test system（MTS，858 Mini Bionix，MTX corporation），loaded with 1.5N·m.Geomagic studio 5.0 soft was applied to splicing the image obtained from realscan USB soft.Finally，the data for each state was collected and processed for One-way ANOVA by SPSS 13.0. LSD test was used to determine the statistical significance of differences.Result：The mean baseline height graft after Smith-Robinson anterior cervical discectomy was 6.86mm.No bone subsidence into vertebrae，end-plates and grafts during the experimentation were noted，implantation of 160% baseline graft appeared more difficult and the laceration of annular ligament occurred in one.Minor graft displacement happened in one case when measuring the motion of flexion and extension at the state of 100% baseline height，no graft extrusion was noted in any specimens.Statistical analysis indicated that the range of motion in flexion，extension and lateral bending of C5/6 decreased significantly at 140% baseline and 160% baseline compared with the baseline height（P<0.05），but no statistical significance were noted between 140% baseline height and 160% baseline height（P>0.05）.The range of motion in lateral bending of C5/6 decreased significantly at 160% baseline height compared with 120% baseline height and the normal state（P<0.05），the rest groups did not show any statistical difference at any direction（P＞0.05）.Conclusion：Distraction after Smith-Robinson anterior cervical discectomy plays an important role in the immediate biomechanical stability of lower cervical spine，and the ideal graft height after single discectomy may be 140% baseline.