[Biomechanical study of bridge-link type combined internal fixation system with mixed-rod in the treatment of long segmental comminuted fracture of femoral shaft].

Objective To observe the biomechanical characteristics of bridge-link type combined internal fixation system (BCFS) with mixed-rod in the treatment of long segmental comminuted fracture of femoral shaft. Methods A total of 16 models of long comminuted segment fracture of femoral shaft with mixed-rod and double-rod were made (8 each structure), and divided into the mixed-rod group and the double-rod group. The axial compression experiment and the radial torsion experiment were carried out on each of the mixed rod group and the double rod group. Four models were randomly selected from the two groups for axial compression experiment and radial torsion experiment, respectively. The changes of axial compression yield load and displacement, and also radial torsional yield load and angle were observed in two groups. At the same time, the maximum load was recorded when the curve had a break point or in a horizontal state, and then calculated the yield load. The data of normal distribution were compared with one-sample t test. Results When the two groups were compressed axially at the same speed, as the axial compression yield load increased gradually, the longitudinal compression displacement of the mixed-rod group was obviously smaller than that in the double-rod group; and the maximum axial compression yield load of the mixed-rod group was greater than that in the double-rod group ((7 517±4)N vs (2 290±4) N, t=1 848.071, P=0.000). When the two groups were twisted radially at the same speed,as radial torsional yield load increased gradually, the radial torsion angle of the mixed-rod group was smaller than that in the double-rod group; and the maximum radial torsional yield load of the mixed-rod group was greater than that in the double-rod group ((61.3±2.0) Nm vs (24.4±2.2)Nm, t=25.201, P=0.000). Conclusions For the long segment comminuted fracture of femoral shaft, the mixed-rod of BCFS can fix fracture more strongly than double-rod in longitudinal direction and maintain the stability of fracture end. The transverse torsion resistance is better than that of the double-rod, and the fatigue resistance is strong. Key words: Bridge-link type combined internal fixation system; Fracture of femoral shaft; Long segment; Comminuted; Biomechanics