中老年人腰椎椎体区域性骨密度差异与力学特性的关系

目的 探讨中老年人腰椎椎体区域性骨密度（BMD）差异与力学特性的关系。方法 取19例中老年人尸体腰椎的运动节段，分别测量每个椎体不同区域的面积骨密度（aBMD）和骨矿含量（BMC），然后分别承受过度压迫负荷导致终板骨折，观察其骨折特点并确定作用于运动节段与终板的极限负荷。结果 19个运动节段标本中，16个（84．2％）发生终板骨折，骨折位于下位椎体的上终板。在单个椎体内部，上终板的aBMD和BMC均小于下终板；椎体上部、中部和下部水平三等份的aBMD和BMC比较，差异均有统计学意义（P＜0．01），且下部1／3的aBMD和BMC值最大；垂直分区比较，无论是二等份还是三等份，aBMD和BMC从前至后均依次升高，差异均有统计学意义（P＜0．01）。围绕椎间盘的上终板aBMD明显高于下终板（P＜0．05），但二者BMC比较，差异却无统计学意义（P＞0．05）。终板的极限负荷与终板和终板下骨的aB．MD和BMC呈正相关。结论 腰椎椎体的区域性BMD存在差异，上终板aBMD低于下终板，椎体前部aBMD低于后部，这可能是临床上椎体压缩性骨折多发于椎体前上部的原因之一。

Bone mineral density and bone mineral content in the lumbar vertebrae and the vetebra''''s biomechanical properties

Objective To determine the variation of bone mineral density(BMD)and bone mineral content (BMC)in cadaveric lumbar vertebrae and investigate their significance in determining fracture modes and biomecha- nical properties.Methods The lumbar motion segments of the spines of 19 cadavers(mean age:56 years)were compressed to failure.The BMD and BMC of the cranial and caudal endplates were determined,along with the BMD and BMC of the upper and lower 1/3 transverse sub-endplate layers and the middle 1/3 transverse layer.The anteri- or,middle and posterior 1/3 vertical parts,anterior and posterior 1/2 vertical parts and the whole BMD and BMC were measured by using dual energy X-ray absorptiometry as well.All the data were analyzed statistically.Results Among the 19 segments,macrography after dissection revealed that 16 had been fractured,about 84.2%.The frac- ture always occurred in the centre or in the anterior part of the endplate.Within a vertebral body,the BMD and BMC of the cranial endplate were less than those of the caudal endplate,and the cranial 1/3 transverse layer and middle layer had lower BMD and BMC readings than the caudal layer.For the vertical region,from the anterior 1/3 to the posterior 1/3,or from the anterior 1/2 to the posterior 1/2,the BMD and BMC increased.For the endplate around the disc,the BMD of upper endplate was higher than that of the lower one,but the BMCs were equal.In one motion segment,the failure load correlated positively with BMD,and with the BMC of the endplate and the sub-endplate bone.Conclusion The variations in BMD and BMC within a vertebra and around a disc can explain why vertebral fractures are concentrated on the upper endplate,and why compressive fractures are always wedge-shaped.This un- derstanding can assist in the placement of inter-vertebral spacers.