Abstract
Background
The purpose of this study was to investigate the stability of dual-taper modular hip implants following impaction forces delivered in varying directions as measured by the distraction forces required to disassemble the components.
Methods
Distraction of the head-neck and neck-stem tapers of dual-taper modular implants with 0°, 8°, and 15° neck angles were measured utilizing a custom-made distraction fixture attached to a servohydraulic materials test machine. Distraction was measured after hand-pressing the components as well as following a simulated firm hammer blow impaction. Impacts to the 0°, 8°, 15° necks were directed axially in-line with the neck, 10° anterior, and 10° proximal to the axis of the neck, respectively.
Results
Distraction forces required to disassemble the neck-stem taper were significantly higher following impaction (1125- 1743 N) when compared to hand pressed assembly (248–302 N). Off-axis impacts resulted in significantly reduced mean (±95% CI) distraction forces (8° neck = 1125 ±117 N; 15° neck = 1212 ±73 N), which were up to 35% lower than the mean distraction force for axial impacts to the 0° neck (1743 ±138 N).
Conclusion
The direction of impaction has a significant effect on the stability of dual taper modular implants, measured by the component distraction force. Greatest stability at the modular interface was achieved with impaction directed in line with the longitudinal axis of the taper junction. Off axis impaction of the 8° and 15° neck led to significantly reduced stability at the neck-stem junction.
