Experimental studies of lateral stress to transverse fractured femora treated with external fixation

As part of a postmortem research project 9 beagle femora were dynamically tested by means of three-point bending. The test device was a spring driven impactor with an impact velocity of 3 m/s. Maximum bending force, deflection and force-deflection history were documented. After the impact transverse fractures were observed in 6 specimens, while another 3 specimens showed short oblique fractures. The fractured femora were treated realistically with external fixation (triax monotube) and again loaded on the impactor. After this treatment of the specimens and dynamic loading comminuted fractures occurred. In 7 cases all 4 pins were distorted. While there was only a small difference between the mean bending force of 751.01 N before and 729.54 N after treatment, a significant difference in terms of deflection and bending stiffness showed with p = 0.0039 for both parameters. This experimental result means that in cases of transverse fractures caused by ventral force only 9.6 % of the initial bending stiffness is obtained after stabilization with external fixation. Considering the fact that the use of external fixation protracts the time to bone consolidation of transverse fractures, this method cannot be designed as the therapy of choice.