Displacement of steel plate for humeral fractures under the load of 100 N and 500 N measured using digital speckle method / 中国组织工程研究

ABSTRACT

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 acompression plate fixation group (not saw off, to simulate fracture healing). Condition bon the basis of sawing off in condition a, one screw was removed on the proximal end. Condition con the basis of condition b, one screw was removed on the distal end. Condition don the basis of condition c, one screw was removed on the distal end. Condition eon 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 CONCLUSION: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.