微创内固定系统和动力髁螺钉固定股骨转子下骨折的生物力学研究

目的比较AO微创内固定系统(less invasive stabilization system,LISS)和动力髁螺钉(dynamiccondylar screw,DCS)固定股骨转子下骨折的生物力学性能,为临床选择内固定器治疗股骨转子下骨折提供理论依据。方法选取甲醛固定股骨近端相似的成年(35～50岁)尸体干股骨标本12根,排除畸形、骨折等病变,将标本随机分成LISS固定组(A组)和DCS固定组(B组),每组6根。每个标本小转子下方1 cm处用斜切机锯断,做成1 cm间隙,模拟粉碎性骨折模型,远端用牙托粉与牙托水包埋固定。标本模拟人体单足站立受力状态,固定于Instron-8874液压伺服力学实验测试机上,行轴向压缩试验和动态疲劳试验,测定抗压性能和标本内侧骨折线两端应变分布情况。结果轴向压缩试验显示,A组在2个应变片处的应变值均较B组相应应变值小,差异有统计学意义(P<0.01);相同载荷下,A组股骨头的垂直下沉位移显著小于B组(P<0.01);载荷600 N时,A组的轴向刚度为(209.06±18.63)N/mm,显著高于B组的(65.79±7.26)N/mm(t=3.787,P=0.004)。动态疲劳试验显示,在相同循环加载周期下,A组股骨头的垂直下沉位移小于B组(P<0.01);当股骨头垂直下沉位移达0.5 mm时,A组内固定所承受的力值及所用的循环加载周期次数均远大于B组,差异有统计学意义(P<0.01)。结论 LISS从生物力学和解剖结构上均能满足股骨转子下骨折内固定要求,具有良好的力学稳定性。经过生物力学比较,LISS内固定较DCS内固定牢固。

BIOMECHANICAL RESEARCH OF LESS INVASIVE STABILIZATION SYSTEM AND DYNAMIC CONDYLAR SCREW IN FIXING SUBTROCHANTERIC FRACTURES OF FEMUR

Objective To compare the biomechanical characteristics of the less invasive stabilization system(LISS) and the dynamic condylar screw(DCS) in the fixation of subtrochanteric fractures of the femur so as to provide theoretical basis for choosing internal xator in clinical flapplication.Methods Twelve cadaveric human femurs(35-50 years old) were selected with similar proximal femur,excluding deformities,fractures,and other lesions.The twelve femur specimens were randomly divided into 2 groups,6 specimens per group.An 1 cm gflap of osteotomy model was made in the proximal femur up to 1 cm below the lesser trochanter to simulate a comminuted subtrochanteric fracture of femur,and the distal end was embedded with denture acrylic and liquid for denture acrylic.Fracture was xed by LISS in group A,and was xed by DCS in group B.The specimens were xed on Instron-8874 servo-hydraulic mechanical testing machine in a single-leg standing position,and the axial compression test and dynamic fatigue test were carried out to compare the compressive strength and the strain distribution at both sides of the fracture line.Results Axial compression test: the strain values of the 2 strain gauges in group A were signi cantly smaller than those in group B(P < 0.01);the vertical down displacement of the femoral head in group A was signi cantly smaller than that in group B(P < 0.01) under the same load;when the load was 600 N,the axial rigidity of group A was(209.06 ± 18.63) N/mm,which was signi cantly higher than that of group B (65.79 ± 7.26) N/mm](t=3.787,P=0.004).Dynamic fatigue test: the vertical down displacement of the femoral head in group A was signi cantly smaller than that in group B in the same cyclic loading cycle(P < 0.01);when the vertical down displacement of the femoral head was 0.5 mm,the force and the cyclic loading cycles in group A were signi cantly larger than those in group B(P < 0.01).Conclusion LISS,which has good mechanical stability,can meet the requirements for subtrochanteric fracture of femur fixation in biomechanics and anatomical structures.It can be proven that the LISS internal xator is rmer than the DCS internal xator by biomechanical comparison.