Krag M H, Beynnon B D, Pope M H, DeCoster T A
McClure Musculoskeletal Research Center, Department of Orthopaedics and Rehabilitation, University of Vermont, Burlington 05405.
J Spinal Disord. 1988;1(4):287-94. doi: 10.1097/00002517-198800140-00002.
Improvement in the strength of the transpedicular screw-vertebra interface by increasing the depth of screw insertion may provide improved performance of spinal implants using such screws. Within human cadaveric vertebrae, we measured the failure strength of Vermont Spinal Fixator (VSF) screws under flexion or torsion loads and of Schanz screws under pull-out loads (along the screw axis). Comparisons between opposite pedicles of vertebral specimens were made at 50 vs. 80% and 80 vs. 100% of maximum available insertion depth. Mean failure strength of VSF screws at 50% depth was 75-77% (depending upon load type) of that at 80% depth; strength for screws at 100% ("to-cortex") depth was 124-154% of that at 80%. Reanalysis of the data from Lavaste shows, contrary to his conclusion, a 26% increase in strength from a 5-mm increase in screw depth of insertion. All these differences were significant (p less than 0.05) by the matched-pairs t test. Benefit from the increased strength of deeper screw placement must be balanced against possible increased operative risk. A "near-approach" x-ray view is suggested here to decrease that presumed operative risk.
通过增加螺钉植入深度来提高椎弓根螺钉与椎体界面的强度，可能会改善使用此类螺钉的脊柱植入物的性能。在人体尸体椎骨中，我们测量了佛蒙特脊柱固定器（VSF）螺钉在弯曲或扭转载荷下以及斯氏针在拔出载荷（沿螺钉轴线）下的破坏强度。在椎体标本相对的椎弓根之间，以最大可用植入深度的50%与80%以及80%与100%进行比较。VSF螺钉在50%深度时的平均破坏强度为80%深度时的75 - 77%（取决于载荷类型）；100%（“至皮质”）深度螺钉的强度为80%深度时的124 - 154%。对拉瓦斯特数据的重新分析表明，与他的结论相反，螺钉植入深度增加5毫米，强度增加26%。通过配对t检验，所有这些差异均具有统计学意义（p小于0.05）。更深的螺钉植入所带来的强度增加的益处必须与可能增加的手术风险相权衡。在此建议采用“近位”X线视图以降低假定的手术风险。
