不同椎弓根螺钉固定及骨水泥强化方法在骨质疏松骶骨上锚定强度的比较

目的:通过比较不同椎弓根螺钉固定及骨水泥强化方法在骨质疏松骶骨上的锚定强度,探讨骶骨椎弓根螺钉松动后的理想补救技术.方法:应用11具成人新鲜骶骨标本,经骨密度测试确认为骨质疏松后,在同一骶骨标本上,依次建立5种骶骨螺钉固定模型,A组,单皮质椎弓根螺钉固定(左侧):B组,双皮质椎弓根螺钉固定(右侧);C组,PMMA钉道强化后单皮质椎弓根螺钉固定(建立于A组螺钉拔出后);D组,PMMA钉道强化后侧翼钉固定(右侧);E组,后凸成形技术支持下的PMMA强化后侧翼钉固定(左侧).应用MTS材料测试机进行轴向拔出测试,记录各种骶骨螺钉固定技术的最大拔出力并进行比较.结果:11具标本的骨密度为0.55～0.79g,cm~2,平均0.71±0.08g/cm~2.A～E组最大拔出力分别为508±128N、685±126N、846±230N、543±121N和702±144N.A组与D组间无显著性差异(P>0.05),且均显著低于B、C和E组(P<0.05);B组与E组间无显著性差异(P>0.05),但两组的拔出力均显著低于C组(P<0.05).结论:在骨质疏松患者的骶骨固定中,双皮质骶骨椎弓根钉较单皮质具有更高的锚定强度.骶骨椎弓根钉一旦发生松动,PMMA钉道强化和后凸成形技术支持下的PMMA强化后的侧翼钉固定均可成为理想的补救手段.

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

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 0.7 l±0.08g/cm~2, ranging from 0.55 to 0.79g/cm~2.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.