国产人工颈椎间盘界面压力对假体-骨界面骨整合的影响

Domestic artificial cervical disc interface pressure distribution and effect of boneimplant interface pressure on osseointegration

目的探讨国产人工颈椎间盘置换术后,界面压力对假体终板-骨界面骨整合的影响。方法取国产人工颈椎间盘置换术后1周的山羊行颈椎CT扫描,建立C_(3、4)椎体及假体三维有限元模型,分析静态模式下假体上、下终板压力分布情况,并根据压力分布范围分区。取人工颈椎间盘置换术后6、12个月山羊,行MircoCT扫描及三维重建,测量各个压力区骨体积分数(bone volume fraction,BVF)、骨小梁数目(trabecular number,Tb.N)、骨小梁厚度(trabecular thickness,Tb.Th)、骨小梁间隙(trabecular separation,Tb.Sp)、骨密度(bone mineral density,BMD)、骨表面积体积比(bone surface/bone volume,BS/BV)、骨小梁模型因子(trabecular pattern factor,Tb.Pf),并进行比较。另取4只正常山羊,切取C_3椎体下终板和C_4椎体上终板标本,制备直径2 mm圆柱形骨块,于取材后即刻以及培养24、48 h行实时荧光定量PCR检测NF-κB受体活化因子配体(nuclear factorκB ligand,RANKL)、骨保护素(osteoprotegerin,OPG)、巨噬细胞集落刺激因子(macrophage colony-stimulating factor,M-CSF)、TGF-β基因表达。根据结果选择合适培养时间的样本进行力学加载后,同上法检测RANKL、OPG、M-CSF、TGF-β基因相对表达量;以同时间点未行力学加载标本作为正常对照。结果 C_(3、4)节段三维有限元模型建立并给予25 N载荷后,在静止状态时人工颈椎间盘上终板压力较大区域在终板中央偏后,下终板压力较大区域在终板中部的前方及两条固定轨道上。按照压力值大小,将终板分为5个区域。Micro-CT扫描观察,假体植入后12个月,上、下终板各区域BMD、Tb.Th、BVF、Tb.N均较6个月时增加(P<0.05),而BS/BV、Tb.Sp、Tb.Pf均降低(P<0.05)。培养24、48 h RANKL、OPG及TGF-β基因相对表达量与取材后即刻比较,差异均有统计学意义(P<0.05);培养24、48 h之间以上基因相对表达量比较差异均无统计学意义(P>0.05)。选择培养24 h样本进行力学加载测试。与对应正常对照组相比,C_3下终板及C_4上终板压力组RANKL、OPG基因相对表达量以及OPG/RANKL明显上调(P<0.05);TGF-β、M-CSF基因相对表达量比较,差异无统计学意义(P>0.05)。结论国产人工颈椎间盘终板压力分布特点不同,其中下终板受到压力稍大。压力不同区域对局部骨整合有重要影响,压力大的区域骨整合情况更佳。在假体终板-骨界面最大压力作用下成骨细胞增殖分子含量增加,有利于局部骨整合。

Objective To analyze the distribution of stress in the upper and lower plates of the prosthesis-bone interface, and the effect of interface pressure on osseointegration. Methods CT scanning was performed on goats at 1 week after artificial cervical disc replacement to establish the finite element model of C3, 4. The stress distribution of the upper and lower plates of the interface was observed. At 6 and 12 months after replacement, Micro-CT scan and three dimensional reconstruction were performed to measure the bone volume fraction （BVF）, trabecular number （Tb. N）, trabecular thickness （Tb. Th）, trabecular separation （Tb. Sp）, bone mineral density （BMD）, bone surface/bone volume （BS/BV）, and trabecular pattern factor （Tb. Pf）. The C3 lower plate and C4 upper plate of 4 normal goat were chosen to made the cylinder of the diameter of 2 mm. The gene expressions of receptor activator for nuclear factor κB ligand （RANKL）, osteoprotegerin （OPG）, transforming growth factor β （TGF-β）, and macrophage colony-stimulating factor （M-CSF） were detected by real time fluorescent quantitative PCR at immediate after cutting and at 24 and 48 hours after culture. The samples of appropriate culture time were selected to made mechanical loading, and the gene expressions of RANKL, OPG, M-CSF, and TGF-β were detected by real time fluorescent quantitative PCR; no mechanical loading samples were used as normal controls. Results Under 25 N axial loading, the stress of the upper plate of C3, 4 was concentrated to post median region, and the stress of the lower plate to middle-front region and two orbits. According to stress, the plate was divided into 5 regions. The Micro-CT scan showed that BMD, Tb.Th, BVF, and Tb.N significantly increased, and BS/BV, Tb.Sp, and Tb.Pf significantly decreased at 12 months after replacement when compared with ones at 6 months （P〈0.05）. At 24 and 48 hours after culture, the gene expressions of RANKL, OPG, and TGF-β were signifi-cantly higher than those at immediate （P〈0.05）, but no significant difference was found between at 24 and 48 hours after culture （P〉0.05）. The mechanical loading test results at 24 hours after culture showed that the RANKL and OPG gene expressions and OPG/RANKL ratio in C3 lower plate and C4 upper plate were significantly up-regulated when compared with controls （P〈0.05）, but no significant difference was shown in TGF-β and M-CSF gene expressions （P〉0.05）. Conclusion Domestic artificial cervical disc endplate has different pressure distribution, the stress of lower plate is higher than that of upper plate. Pressure has important effect on local osseointegration; the higher pressure area is, the osseointegration is better. Under the maximum pressure in interface, the osteoblast proliferation will increase, which is advantageous to the local osseointegration.