Evaluation of a new method of small fragment fixation in a medial malleolus fracture model

Objective: To evaluate a new method of small fragment fixation in a medial malleolus fracture model. Design/Methods: The authors measured the pullout strength, resistance to sh ear stress, and speed of insertion of 4.0-millimeter partially threaded can cellous screws, 2.4-millimeter smooth K-wires, and a small fragment fixatio n system with 2.2-millimeter threaded K-wires. Pullout strength was tested in eighty-one synthetic foam blocks and resistance to shear stress in thirt y synthetic tibias by use of a servohydraulic testing machine. Six randomiz ed time trials with the threaded K-wires and cancellous screws were also co nducted. Results: Pullout strength increased with increasing foam density, increasin g insertion depth, and varied with fixation method (p < 0.05). Maximum pull out strengths were as follows: partially threaded cancellous screws, 730 +/ - 4 Newtons; threaded K-wires, 316 +/- 12 Newtons; and smooth K-wires, 172 +/- 5 Newtons. Percent difference in pullout strength between the partially threaded cancellous screw and threaded K-wire diminished with increased de pth of insertion and increased foam density. Offset axial load to initiate fracture displacement in a synthetic tibia model averaged 1540 +/- 138 Newt ons for the partially threaded cancellous screws, 1,318 +/- 117 Newtons for the threaded K-wires, and 1.287 +/- 121 Newtons for the smooth K-wires (p > 0.05). Average time of fixation of a medial malleolar fragment by orthope dic surgeons with a variety of experience levels in a synthetic tibia with two threaded K-wires (114 +/- 8 seconds) was significantly faster (p < 0.05 ) than with two partially threaded cancellous screws (207 +/- 20 seconds). Conclusions: Threaded K-wires show substantial pullout strength and similar resistance to offset axial load when compared with partially threaded canc ellous screws. These threaded K-wires offer an alternative for the internal fixation of medial malleolus fractures.