Evaluation of a New Method of Small Fragment Fixation in a Medial Malleolus Fracture Model

Abstract

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 shear stress, and speed of insertion of 4.0-millimeter partially threaded cancellous screws, 2.4-millimeter smooth K-wires, and a small fragment fixation system with 2.2-millimeter threaded K-wires. Pullout strength was tested in eighty-one synthetic foam blocks and resistance to shear stress in thirty synthetic tibias by use of a servohydraulic testing machine. Six randomized time trials with the threaded K-wires and cancellous screws were also conducted.

Results: 

Pullout strength increased with increasing foam density, increasing insertion depth, and varied with fixation method (p < 0.05). Maximum pullout 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 depth of insertion and increased foam density. Offset axial load to initiate fracture displacement in a synthetic tibia model averaged 1540 ± 138 Newtons 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 orthopedic 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 cancellous screws. These threaded K-wires offer an alternative for the internal fixation of medial malleolus fractures.