Li Nan, He Da, Xing Yonggang, Lv Yanwei, Tian Wei
Department of Spine Surgery, Beijing Jishuitan Hospital, 31 Xinjiekou Dongjie, Beijing, 100035, China.
Clinical Statistics and Epidemiology Research Office, Traumatology and Orthopaedics Research Institute of Beijing, Beijing Jishuitan Hospital, Beijing, China.
J Orthop Surg Res. 2015 Jan 24;10:6. doi: 10.1186/s13018-015-0157-0.
Lateral pedicle wall perforations occur frequently during pedicle screw insertion. Although it is known that such an occurrence decreases the screw pull-out strength, the effect has not been quantified biomechanically.
Twenty fresh cadaveric lumbar vertebrae were harvested, and the bone mineral density (BMD) of each was evaluated with dual-energy radiography absorptiometry (DEXA). Twenty matched, 6.5-mm pedicle screws were inserted in two different manners in two groups, the control group and the experimental group. In the control group, the pedicle screw was inserted in a standard fashion taking adequate precaution to ensure there was no perforation of the wall. In the experimental group, the pedicle screw was inserted such that its trajectory perforated the lateral wall. Group assignments were done randomly, and the maximal fixation strength was recorded for each screw pull-out test with a material-testing system (MTS 858 II).
The average BMD for both groups was 0.850 g/cm(2) (0.788-0.912 g/cm(2)). The average (and standard deviation) maximal pull-out forces were 1,015.8 ± 249.40 N for the experimental group and 1,326.0 ± 320.50 N for the control group. According to a paired t-test, the difference between the two groups was statistically significant (P < 0.001).
The results of this study confirm that the maximal pull-out strength of pedicle screws decreases by approximately 23.4% when the lateral wall is perforated.
椎弓根螺钉置入过程中，椎弓根侧壁穿孔屡见不鲜。尽管已知这种情况会降低螺钉拔出强度，但尚未对其生物力学影响进行量化。
获取20具新鲜尸体腰椎，采用双能X线吸收法（DEXA）评估每具腰椎的骨密度（BMD）。将20枚匹配的6.5毫米椎弓根螺钉以两种不同方式分别植入对照组和实验组。对照组以标准方式植入椎弓根螺钉，并采取充分预防措施确保侧壁无穿孔。实验组则以使其轨迹穿破侧壁的方式植入椎弓根螺钉。随机进行分组，使用材料测试系统（MTS 858 II）对每次螺钉拔出试验记录最大固定强度。
两组的平均骨密度均为0.850克/平方厘米（0.788 - 0.912克/平方厘米）。实验组的平均（及标准差）最大拔出力为1015.8±249.40牛，对照组为1326.0±320.50牛。根据配对t检验，两组之间的差异具有统计学意义（P < 0.001）。
本研究结果证实，当侧壁穿孔时，椎弓根螺钉的最大拔出强度降低约23.4%。
