数字散斑法测量加载100N与500N肱骨干骨折钢板固定下的位移

Displacement of steel plate for humeral fractures under the load of 100N and 500N measured using digital speckle method

背景:目前国际上还没有统一骨组织力学性能测试的试验标准。以往将传统传感器引入骨折位移的研究,存在精度低、高消耗成本等问题。目的:采用数字散斑法测量肱骨骨折内固定后钢板螺钉的位移特点。方法:取8根肱骨,于其中点横断,制造肱骨中段骨折模型。将标本用8孔钢板固定,骨折线两端各使用4枚螺钉。将实验模型设计成5种状态进行对比分析:状态a是骨折后加压钢板坚强内固定组(未锯断,模拟骨折愈合),状态b是在状态a锯断后基础上近端去1枚螺钉,状态c是在状态b的基础上远端去1枚螺钉,状态d是在状态c的基础上近端去1枚螺钉,状态e是在状态d的基础上远端去1枚螺钉。螺钉编号顺序从上到下依次为1-8号,即骨折线上位螺钉为1-4号,骨折线下位螺钉为5-8号。用电子万能试验机进行加载100 N与500 N测量,通过相关软件计算位移。结果与结论:在不同载荷间的总位移比较,差异有显著性意义(F=49.155,P<0.001),即随着加载力的增大,5种模拟状态下第4钉、第5钉的总位移值均呈逐渐增大趋势。提示骨折线两端的2枚螺钉是承受较多应力的部位(应力集中),易于发生断裂,应选用比现有螺钉直径增大1-2.5 mm的螺钉,增加骨折线旁固定螺钉的稳定性以避免断钉等后遗症。

BACKGROUND：There is no unified measure of bone tissue mechanical property test at present. The study concerning traditional sensor for fracture displacement had some problems such as low precision, and high consumption cost. OBJECTIVE：To measure the displacement of plate and screw after internal fixation for fracture of humerus using digital speckle method. METHODS：A total of eight humeral specimens were taken. The steel plate fixation model in the humerus 1/2 was made. The specimens were fixed using eight-hole steel plate, and four screws were fixed on each end of fracture line. Five conditions of experimental model were designed for comparative analysis. Condition a：compression plate fixation group （not saw off, to simulate fracture healing）. Condition b：on the basis of sawing off in condition a, one screw was removed on the proximal end. Condition c：on the basis of condition b, one screw was removed on the distal end. Condition d：on the basis of condition c, one screw was removed on the distal end. Condition e：on the basis of d, one screw was removed on the distal end. The screws were numbered No. 1-8 from top to bottom. That is, the screws on upper fracture line were numbered No. 1-4, and those on the lower fracture line were numbered No. 5-8. The specimens were instal ed on electronic universal testing machine, and loaded 100 N and 500 N. The displacement was calculated using the related software. RESULTS AND ONCLUSION：Significant differences in total displacement were detected under different loads （F=49.155, P〈0.001）. With increased load, the total displacement of the fourth and fifth screws gradual y increased under five kinds of conditions. These indicated that the two screws on the two ends of the fracture line endured more stresses （stress concentration）, and easily broke. It would be better to choose the screw with the screw diameter of 1-2.5 mm bigger than the present one in order to increase its stability to avoid the breakage of screws.