Comparison of anchoring strengths in osteoporotic sacrum among different pedicle screws and bone cement augmentation/

English Keywords:Osteoporosis  Lumbosacral fusion  Sacral pedicle screw  Polymethylmethacrylate augmentation  Biomechanics

English Abstract:

  【Abstract】　Objective：To compare the maximum pull-out strengths in osteoporotic sacrum among unicortical，bicortical pedicle screws and three salvage methods using polymethylmethacrylate（PMMA） augmentation and determine the most favorable salvage technique for loosened pedicle screw.Method：11 fresh human osteoporotic cadaveric sacrum were used in this study.Following sequential establishments of five sacral screw instrumentations on the same sacrum，screw pull-out load tests were conducted on a MTS material testing machine defined as follows，group A，unicortical pedicle screw（on left side），group B，bicortical pedicle screw（on right side），group C，unicortical pedicle screw with traditional PMMA augmentation（secondary to the pull-out test of group A），group D，lateral wing screw with traditional PMMA augmentation（on right side），group E，lateral wing screw with kyphoplasty-assisted PMMA augmentation.The maximum pull-out forces of five screw instrumentations were measured and compared biomechanically.Result：The average BMD of 11 specimens was 0.71±0.08g/cm2，ranging from 0.55 to 0.79g/cm2.The maximum pull-out strengths for group A to E were 508±128N，685±126N，846±230N，543±121N and 702±144N respectively.No significant difference with respect to pull-out strength was detected between group A and D（P>0.05），however，these two techniques exhibited remarkably lower pull-out strength than that in group B，C and E（P<0.05）.Statistical difference on pull-out strength was not evidenced between group B and E（P>0.05），nevertheless，the two instrumentations showed significantly lower pull-out strength than that in group C（P<0.05）.Conclusion：For sacral screw fixation in osteoporotic patient，bicortical pedicle screw has significantly higher fixation strength than unicortical screw.Once the loosening of pedicle screw occurs，the traditional PMMA augmentation or lateral wing screw with kyphoplasty-assisted PMMA augmentation may serve as a suitable salvage technique.