[Biomechanical research of different types of femoral fracture fixed by bridge system with mixed-rod and double-rod].

Objective: To determinate the effective axial compression yield loads of different types of femoral fracture fixed by bridge system with mixed-rod and double-rod to select the internal fixation method. Methods: A total of 32 polyformaldehyde mixed-rod and double-rod models of long oblique, long spiral, wedge-shaped with large fragment and supracondylar fractures were made. Among them, there were 4 mixed-rod models and 4 double-rod models for each type of fractures. Axial compression test was conducted on all fracture models using the microcomputer-controlled electronic universal testing machine. When the compression displacement was 2.0 mm, the axial compression yield loads, which were the maximum effective loads, and the average load was calculated and compared with the reference value of 2 475 N. When the compression displacement was less than 2.0 mm, if there was an obvious break point in the load-displacement curve, the maximum load was invalid. Results: The average loads of models for different types of femoral fractures were as follows: the load of long oblique fracture with mixed-rod and double-rod models was (7 603.5±471.7) N and (4 117.5±29.2) N, respectively; the load of long spiral fractures was (2 890.1±139.4) N and(2 500.6±74.5)N, respectively; the load of wedge-shaped fracture with larger fragment was (5 110.2±489.0) N and(4 234.3±256.0)N, respectively; and the load of supracondylar fracture was (9 071.3±1 444.3) N and(9 403.1±1 649.6)N, respectively. The average loads of all the mixed-rod and double-rod models of femoral fractures were greater than the reference value. Conclusion: For long oblique, long spiral, wedge-shaped with large fragment and supracondylar fractures of the femur, the double-rod of bridge system can meet the fixation requirements, and it is recommended to use the double-rod of bridge system in terms of open reduction and internal fixation.