动力加压锁定钉板系统与空心拉力螺钉固定PauwelsⅢ型股骨颈骨折的生物力学比较

Biomechanical comparison of Kangli hollow screws with sliding compression locking plate system and conventional cannulated lag screws for fixation of type Pauwels III femoral neck fracture

目的比较股骨颈动力加压锁定钉板系统与空心拉力螺钉固定Pauwelsm型股骨颈骨折的生物力学性能。方法选取7具人体股骨防腐标本，按照Pauwels角=70°将股骨颈锯断制成Pauwelsm型股骨颈骨折模型，使用传统空心拉力螺钉及股骨颈动力加压锁定钉板系统分别固定骨折（两种方法先选其一固定，而后拆除后再使用另一种方法固定）；取股骨干中段截断，股骨干与水平面成750置于包埋模具内并固定在材料试验平台上，在股骨颈骨折线两边安装光学传感器；分别加载垂直、侧方及旋转载荷各三次，其中垂直及侧方设定最大载荷为400N，旋转载荷为2．5N·m，记录第三次垂直、侧方及旋转三种载荷下骨折断端间的滑动位移或相对角位移，计算两种内固定物对抗不同方式载荷的刚度值并进行对比。另外，将一名25岁健康男性志愿者的左侧股骨cT数据导入相应软件并制作PauwelsⅢ型股骨颈骨折模型，同时将空心拉力螺钉及股骨颈动力加压锁定钉板系统材料属性进行赋值后最终制成骨折固定后的有限元模型，在静力载荷加载下进行有限元分析，测量兴趣部位应力值及骨折断端间移位值并进行对比。结果尸体标本测试在垂直、侧方及旋转载荷加载测试中，股骨颈动力加压锁定钉板系统组相应的刚度值分别为（3904±1148）N／mm，（4324±1234）N／mm和（11．45±4．95）N·m／°，而空心拉力螺钉组分别为（3020±1150）N／mm，（3020±854）N／mm和（6．53±4．83）N·m／°；两组比较，差异均有统计学意义（t=2．7194，4．7694和2．9424；P=0．0347，0．0050和0．0423）。有限元分析显示在垂直静力载荷为600N的作用下，股骨颈动力加压锁定钉板系统固定时，股骨及螺钉上的最大应力值分别为：40．1MPa和126．4MPa，空心拉力螺钉固定时相应的应力值为：98．1MPa和145．5MPa，前者均小于后者；而骨折断端间的最大压应力值，股骨颈动力加压锁定钉板系统固定时为14．37MPa，空心拉力螺钉固定时为9．39MPa，前者远大于后者。骨折断端间移位裂隙大小对比显示股骨颈动力加压锁定钉板系统固定明显小于空心拉力螺钉固定。结论股骨颈动力加压锁定钉板系统能为Pauwelsm型股骨颈骨折提供更为坚强的固定，生物力学性能更好，股骨及螺钉断裂的风险更低，更有利于骨折的愈合。

Objective To compare the biomechanical performance of Kangli hollow screws with sliding compression locking plate system （KHS） and conventional cannulated lag screws for fixation of type Pauwels III femoral neck fracture. Meth- ods 7 cadaveric femurs were selected, vertical fractures （Pauwels III fracture, at 70° to the horizontal） were artificially conducted in these cadaveric proximal femurs by an orthopaedic surgeon and fixed by KHS screws with plate system or conventional cannulat- ed lag screws. Samples were positioned at 75° of the femoral shaft to the horizontal, embedded in the mould and fixed in the experi- mental console. Optical sensors were set at the femoral neck around the osteotomy line. Then the loading were input in the vertical, horizontal lateral direction and rotating direction around the femoral neck axis, the maximal and minimal values between the frac- tured fragments and the corresponding values of the loading were recorded. The values of stiffness in three directions were calculat- ed and compared. The CT data of the left femur of a 25 year-old healthy male volunteer was input into the corresponding softwareand vertical femoral neck fracture model was generated. Two finite element analysis models were obtained after the fracture being fixed using these two different implants, and the Von Mises stress distribution on the femur, implants and the interface between the fractured fragments and the relative motion between the fractured fragments were compared. Results In the vertical, horizontal lateral direction and rotating direction around the femoral neck axis, the stiffness of the KHS were 3 904± 1 148 N/mm, 4 324± 1 234 N/mm and 11.45±4.95N·m/° respectively, higher than those of the CSs method with the values of 3 020±1 150 N/ram, 3 020±854 N/ram and 6.53±4.83N·m/° respectively. The differences between the two groups were statistically significant （t=2.7194, 4.7694 and 2.9424;P=0.0347, 0.0050 and 0.0423）. In the finite element analysis test, the maximal Von Mises stress values distrib- uting on the femur and the screws in the KHS group were 40.1 MPa and 126.4 MPa, and those in the CSs group were 98.1 MPa and 145.5 MPa respectively, and both values of the former were lower than the latter. But the Von Mises stress value on the inter- face between the fractured fragments in the KHS group was 14.37 MPa, which was much higher than that in the CSs groupwhich was 9.39 MPa. The gap at the fracture site of the CSs fixation model was dramatically larger than that of KHS fixation model. Con- elusion The KHS screws and plate system could provide better immobilization effect for vertical femoral neck fracture compared to the cannulated lag screws. The risk of the screws failure was lower and the fracture union would be easier to obtained by the fixa- tion of KHS screws with olate system.