Abstract
Introduction
In this study, we aimed to investigate the effect of the topography of the female taper surface on taper wear.
Patients/Materials & Methods
We measured volumetric material loss at the female taper surface of the first consecutive 36mm MoM hips received at our centre. The MoM hips were from a single manufacturer and possessed matching: head size (36mm); taper geometry (5.65 degree 12 14 tapers); and metallurgy (cobalt chrome female taper mated with a titanium stem). Volume loss was measured with a coordinate measuring machine using validated methods. Surface roughness was measured using a Surftest SJ400. There were 111 head tapers available for analysis. The majority had been revised secondary to ARMD, and a minority for loosening. The mean duration of implantation was 56 months. Volumetric wear values were log normalised in order to construct a multiple regression model to investigate the interaction of head offset, the head taper angle and the Rp value of the female taper surface. Rp is a roughness parameter, which is a measure of the peaks above the plateau of a surface.
Results
The median (range) volumetric loss from the female taper surfaces was 0.132mm3 (0.008–2.149). Median Rp value was 1.94 microns (0.50 to 6.01). Multiple regression model returned an R2 value of 0.43 (p < 0.001) meaning that the Rp value of the female surface, the head offset, duration of implantation and the taper angle explained 43% of the variation in volumetric wear rates. Rp was the dominant variable.
Discussion & Conclusion
The topography of the female taper surface appears to be an important factor in material loss from the taper junction in MoM hips. There was an unexpectedly wide variation in surface finishes in our sample set despite the fact that a single product from a single manufacturer was analysed.
