Abstract
Introduction
Since the introduction of modular hip taper junctions, corrosion has been studied yet the clinical effect remains unclear. Mechanically assisted corrosion and crevice corrosion are thought to be the primary clinical processes driving taper corrosion. Like all corrosion reactions, these processes require the taper junction to be in contact with an electrolyte. This study investigates the effect of sealing the taper junction from the environment on the mechanically-induced corrosion of a modular hip taper junction.
Methods
A short-term corrosion fatigue test was conducted with Ti6Al4V 12/14 taper coupons coupled with CoCrMo 12/14 taper 28mm+12 heads (DePuy Synthes, Warsaw, IN). Ten specimens were assembled with a 1.1 kN press load and sealed with silicone sealant (Dow-Corning 732 Multi-Purpose Sealant). Prior to assembly five of these specimens were assembled with the taper junction having been wetted with phosphate buffered saline before assembly; the rest were assembled dry. Specimens were then immersed in phosphate buffered saline and a potentiostat was used to maintain the potential of the specimen at −50mV vs. Ag/AgCl. Incrementally larger loads were applied to the head of the specimen until a 4000N maximum load was reached. The average currents generated during this test was used to assess the corrosion performance of the specimens. The data from the sealed specimens was compared to a control group, which were wetted before assembly but not sealed.
Results
In all cases the corrosion of the sealed specimens did not appear to increase in response to the cyclic load; throughout the test, the corrosion did not increase over the baseline anodic current of roughly 0.25 μA. In contrast, the unsealed controls experienced average corrosion currents of around 5 μA at the maximum load, and an average current of 2.0±0.93 µA over the entire test. The wet and dry sealed assembly specimens both resulted in significantly lower average currents of 0.24±0.09 µA and 0.25±0.09 µA, respectively.
Discussion
Test specimens with sealed taper junctions to prevent fluid and ion ingress and egress resulted in no measurably increased corrosion currents compared to the baseline currents in the ambient fluid. The wetted sealed specimens might possibly be subject to corrosion; however the corrosion process and effects in this case may be isolated within the taper junction. This test indicates mechanically assisted corrosion does not occur if the taper junction is not exposed to an electrolyte.
Significance
This study demonstrates that mechanically induced corrosion can be greatly reduced or prevented by sealing the taper junction to prevent the ingress of electrolyte.
