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.


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.
Rovinsky
D
D
Department of Orthopaedic Surgery, University of California, San Francisco, USA.
Haskell
A
A
Liu
Q
Q
Paiement
G D
GD
Robinovitch
S
S
D001863:Bone Screws / Q000592:standards*; D001864:Bone Wires / Q000592:standards*; D019245:Compressive Strength; D004867:Equipment Design; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D008422:Materials Testing / Q000295:instrumentation / Q000379:methods; D013718:Tensile Strength; D013978:Tibial Fractures / Q000601:surgery*; D013997:Time Factors; D016474:Weight-Bearing