Yu Binsheng, Zhuang Xinming, Li Zemin, Zheng Zhaomin
Department of Spine Surgery, the First Affiliated Hospital, Sun Yat-sen University, Guangzhou Guangdong, 510700, P.R. China.
Zhongguo Xiu Fu Chong Jian Wai Ke Za Zhi. 2010 Feb;24(2):211-4.
To biomechanically compare the maximum pull-out strengths among two pedicle screws and three salvage techniques using poly methylmethacrylate (PMMA) augmentation in osteoporotic sacrum, and to determine which PMMA augmentation technique could serve as the salvage fixation for loosening sacral pedicle screws.
Eleven sacral were harvested from fresh adult donated cadavers, aged from 66 to 83 years (average 74.4 years) and included 5 men and 6 women. Radiography was used to exclude sacral that showed tumor or inflammatory or any other anatomic abnormalities. Following the measurement of bone mineral density, five sacral screw fixations were sequentially established on the same sacrum as follows: unicortical pedicle screw (group A), bicortical pedicle screw (group B), unicortical pedicle screw with the traditional PMMA augmentation (group C), ala screw with the traditional PMMA augmentation (group D), and ala screw with a kyphoplasty-assisted PMMA augmentation technique (group E). According to the sequence above, the axial pull-out test of each screw was conducted on a MTS-858 material testing machine. The maximum pull-out forces were measured and compared. The morphologies of PMMA augmented screws after being pulled-out were also inspected.
The average bone mineral density of 11 osteoporotic specimens was (0.71 +/- 0.08) g/cm2. By observation of the pull-out screws, groups C, D, E showed perfect bonding with PMMA, and group E bonded more PMMA than groups C and D. The maximum pull-out forces of groups A, B, C, D, and E were (508 +/- 128), (685 +/- 126), (846 +/- 230), (543 +/- 121), and (702 +/- 144) N, respectively. The maximum pullout strength was significantly higher in groups B, C, and E than in groups A and D (P < 0.05), and in group C than in groups B and E (P < 0.05). There was no significant difference in pull-out strength between groups A and D, and between groups B and E (P > 0.05).
For sacral screw fixation of osteoporotic patients with bone mineral density more than 0.7 g/cm2, bicortical pedicle screw could acquire significantly higher fixation strength than the unicortical. Once the loosening of pedicle screw occurs, the traditional PMMA augmentation or ala screw with kyphoplasty-assisted PMMA augmentation may serve as a suitable salvage technique.
通过生物力学方法比较两种椎弓根螺钉及三种采用聚甲基丙烯酸甲酯（PMMA）强化技术的补救技术在骨质疏松性骶骨中的最大拔出强度，以确定哪种PMMA强化技术可作为骶椎弓根螺钉松动后的补救固定方法。
从66至83岁（平均74.4岁）的新鲜成人捐赠尸体上获取11块骶骨，其中男性5例，女性6例。通过X线摄影排除显示有肿瘤、炎症或其他解剖异常的骶骨。在测量骨密度后，在同一骶骨上依次建立五种骶骨螺钉固定方式：单侧皮质椎弓根螺钉（A组）、双侧皮质椎弓根螺钉（B组）、采用传统PMMA强化的单侧皮质椎弓根螺钉（C组）、采用传统PMMA强化的翼状螺钉（D组）以及采用椎体后凸成形辅助PMMA强化技术的翼状螺钉（E组）。按照上述顺序，在MTS - 858材料试验机上对每个螺钉进行轴向拔出试验。测量并比较最大拔出力。还检查了拔出后PMMA强化螺钉的形态。
11个骨质疏松标本的平均骨密度为（0.71±0.08）g/cm²。通过观察拔出的螺钉，C组、D组、E组与PMMA结合良好，且E组结合的PMMA比C组和D组更多。A组、B组、C组、D组和E组的最大拔出力分别为（508±128）、（685±126）、（846±230）、（543±121）和（702±144）N。B组、C组和E组的最大拔出强度显著高于A组和D组（P<0.05），C组高于B组和E组（P<0.05）。A组和D组之间以及B组和E组之间的拔出强度无显著差异（P>0.05）。
对于骨密度大于0.7g/cm²的骨质疏松患者的骶骨螺钉固定，双侧皮质椎弓根螺钉的固定强度明显高于单侧皮质椎弓根螺钉。一旦椎弓根螺钉发生松动，传统的PMMA强化或椎体后凸成形辅助PMMA强化的翼状螺钉可作为合适的补救技术。
