重度骨质疏松腰椎中椎弓根螺钉稳定性与骨水泥注射剂量的相关性

Study on the relationship between stability of pedicle screw and injected volume of polymethylmethacrylate in severe osteoporotic lumbar vertebrae

目的 :比较重度骨质疏松腰椎中不同剂量骨水泥强化椎弓根螺钉的稳定性,分析螺钉稳定性与骨水泥剂量间的相关关系及初步探索注射PMMA的合适剂量。方法:18个新鲜腰椎标本来自4具新鲜尸体(男性1名和女性3名,平均年龄65±9岁),测量各椎体的骨密度(bone mineral density,BMD)后将18个腰椎标本的36侧椎弓根随机分为6个实验组(A^F组)。相同方法制备钉道后,从A组到F组中,依次向钉道内注入0ml、1.0ml、1.5ml、2.0ml、2.5ml、3.0ml PMMA后拧入普通椎弓根螺钉。待骨水泥硬化后进行X线检查观察螺钉周围骨水泥的分布情况,随后进行轴向拔出实验并测量最大轴向拔出力(the maximum axial pullout strength,Fmax)。采用单因素方差分析和LSD检验比较各组中的BMD和Fmax的差异。Fmax和PMMA剂量之间进行相关性分析。结果:所有腰椎的BMD均小于0.6g/cm2,T值均小于-3.5,根据WHO的标准均诊断为重度骨质疏松椎体,各组中BMD之间的差异无统计学意义(P=0.799)。A组中,螺钉周围未见任何PMMA;B^F组中,PMMA相对均匀地分布于螺钉周围的骨质中。所有腰椎中螺钉位置良好,均未见明显PMMA渗漏。A^F组的Fmax分别为358.50±86.00N、442.67±96.02N、532.00±103.18N、740.67±120.90N、841.50±133.42N和1111.50±158.57N。与A组相比,B^F组的Fmax的提高程度分别为23.48%、48.40%、106.60%、134.73%和210.04%。A组和B组之间,B组和C组之间,E组和F组之间Fmax的差异均不具有统计学意义(P=0.230,P=0.203,P=0.152),其余各组间的差异均具有统计学意义(P<0.05)。Fmax与PMMA剂量之间存在显著的正相关关系(Pearson相关系数r=0.877,P<0.05)。结论 :PMMA可以提高重度骨质疏松腰椎中椎弓根螺钉的稳定性,螺钉稳定性与PMMA剂量成显著的正相关关系。在一定范围内,注射PMMA和增加PMMA的剂量并不能显著增加螺钉的稳定性。生物力学研究表明,重度骨质疏松腰椎中提高螺钉稳定性时注射PMMA的合适剂量是3ml。

Objectives： To compare the stabilities of pedicle screw augmented with different volumes of poly-methylmethacrylate（PMMA） in severe osteoporotic lumbar vertebrae, and to investigate the relationship between screw stability and volume of PMMA in severe osteoporotic lumbar vertebrae. Methods： Eighteen lumbar vertebrae were obtained from four fresh-frozen human cadaveric spines（1 male and 3 female specimens with an average of 65±9 years old）. Thirty-six pedicles from eighteen lumbar vertebrae were randomly divided into six groups（group A to group F） after measurement of bone mineral density（BMD） of all samples. A pilot hole was prepared in advance by using the same method in all samples. Then, the pilot hole was filled with different volume of PMMA（0ml, 1.0ml, 1.5ml, 2.0ml, 2.5ml, 3.0ml） followed by insertion of screw in group A, B, C, D,E and F, respectively. After that, X-ray and axial pullout test were performed in all groups, and the maximum axial pullout strength（Fmax） was measured. The one-way ANOVA and LSD test were used to detect the differences on BMD and Fmax among six groups. Relationship between Fmax and the volume of PMMA was assessed by using linear regression analysis. Results： All BMD values were less than 0.6g/cm2 and all T values were less than-3.5, therefore, all samples in six groups were diagnosed with severe osteoporotic lumbar vertebrae according to World Health Organization definition. There was no significant difference in BMD among six groups（P=0.799）. No PMMA was found around screw in group A. PMMA was found evenly wrapping up screw in group B-F. No malposition of screw and leakage of PMMA were found in all lumbar vertebrae. The maximum axial pullout strength（Fmax） in group A-F was 358.50 ±86.00 N, 442.67±96.02 N,532.00±103.18 N, 740.67±120.90 N, 841.50 ±133.42 N and 1111.50 ±158.57 N, respectively. Fmax in group B-F increased 23.48%, 48.40%, 106.60%, 134.73% and 210.04% respectively compared with that in group A.There were no significant differences for Fmax between group A and B, group B and C, and group E and F（P=0.230, P=0.203, P=0.152, respectively）. While significant differences were found between every other two groups（P0.05）. There was significantly positive correlation between Fmax and the volume of PMMA（r=0.877,P0.05）. Conclusions： PMMA can enhance stability of pedicle screw in severe osteoporosis, and the screw holding strength increases with the increment of the PMMA volume in a limited range. Injection of 3ml PMMA is considered the preferred volume to improve the pedicle screw holding strength in severe osteoporotic lumbar vertebrae.