Tribological property of the cobalt-chromium femoral head with different regions of wear in total hip arthroplasty

The tribological properties of engineering and biological materials have been investigated at microscale levels through the calculation of the surface roughness and frictional coefficient using atomic force microscopy (AFM). Although a number of previous studies have reported the frictional coefficients of diverse bearing materials in total hip arthroplasty (THA), the relationship between the surface roughness and frictional coefficient of bearing materials of THA have not been reported, and furthermore, the tribological properties for different wear regions of a cobalt-chromium (Co-Cr) femoral head have not been well identified. Therefore, the objective of this study is to investigate the relationships between the surface roughness, frictional coefficient, and hardness for both the main-wear and the least-wear regions of a Co-Cr femoral head 10 years after THA. The average Vickers hardness of the Co-Cr femoral head was 380.7 +/- 11.3 HV. With the scanned area of 25 mu m x 25 mu m through AFM, the frictional coefficients of the main-wear and the least-wear regions were 0.229 +/- 0.054 and 0.243 +/- 0.059, respectively, and showed no statistical differences between these two regions (p = 0.449). However, differences in the surface roughness (R-q) between the main-wear region (R-q = 96.5 +/- 26.2 nm) and the least-wear region (R-q = 17.7 +/- 4.2 nm) were statistically significant (p < 0.0001). The results of the current study suggest that the frictional property of the Co-Cr femoral head is not significantly correlated with its surface roughness, and also provide guidelines for improving the surface characteristics of metallic implant materials.