Evaluation of Strength at the Acrylic–Pin Interface for Variably Treated External Skeletal Fixator Pins

Abstract

To report pullout force to failure at the acrylic-pin interface for variably treated 3.2 mm external skeletal fixator pins. In vitro biomechanical evaluation. 3.2 mm external skeletal fixator pins in polymethylmethacrylate bars. 3.2 mm external skeletal fixator pins were used for each of 5 treatment groups: polished, unpolished, 3 notched, 5 notched, and machine knurled. Each pin was seated into a 2-cm-diameter acrylic connecting bar and tested in pullout force to failure. Each group consisted of 6 pins. The force required to remove the pins from the acrylic bar was measured and compared between groups. Significant differences between treatment groups were determined (P<.05). Within a construct group failure mode was consistent. Fracture of the acrylic bar was only seen with knurled pin ends. When using 2 cm acrylic bars in external skeletal fixation (ESF), a knurled pin shaft or a pin surface with 5 notches should be considered to improve the overall stability of the ESF construct.