Abstract
Introduction
Recent studies on large diameter femoral head hip replacements have implicated the modular taper junction as one of the significant sources of wear and corrosion products and this has been attributed to increased torque and bending on the taper interface. The aim of this study was to assess the effect of frictional torque and bending moment on fretting corrosion at the taper junction and to investigate whether different material combinations also had an effect.
Patients/Materials & Methods
We examined 1) Cobalt Chromium (CoCr) heads on CoCr stems 2) CoCr heads on Titanium alloy (Ti) stems and 3) Ceramic heads on CoCr stems. In test 1 increasing torque was imposed by offsetting the femoral stem in the anterior posterior plane in increments of 0 mm, 4 mm, 6 mm and 8 mm where the force generated was equivalent to 0Nm, 9Nm, 14Nm and 18Nm. In Test 2 we investigated the effect of increasing bending moment by offsetting the application of axial load from the midline in the medial-lateral (ML). Offset increments equivalent to +0, +7 and +14 heads were used. For each test we used n=3 for each different material combination.
Results
Significantly higher currents and amplitudes were seen with increasing frictional torque for all material combinations, however titanium alloy stems showed the highest corrosion. Increasing bending moments associated with using larger off-set heads produced more corrosion; with titanium alloy stems generally performing worse than cobalt chrome stems. Using ceramic heads did not prevent corrosion, but this was significantly reduced in all loading configurations.
Discussion & Conclusion
This is the first study to quantify corrosion associated with different material combinations and loading conditions. Increasing frictional torque and bending, together with the material combination have a significant effect on the fretting corrosion at the taper modular junction. The best performing material combination was ceramic on CoCr.
