2.3. Surface Roughness Measurements

The surface roughness of all 12 ceramic femoral heads was measured using a contact profilometer (Hommel Tester T8000, Hommel Werke, Koeln, Germany) equipped with a diamond stylus (tip radius 0.020 mm). Scanning operations were performed at ten points for each femoral head—one point on the pole and three random points on three different planes identified according to a standardized protocol [23]. Sampling lengths were taken using a cut-off of 0.08 mm and tracing length of 0.48 mm. Three main indicators were used to characterize the roughness of the femoral heads, namely R_a, R_t, and R_sk. R_a represents the arithmetical mean height of the roughness irregularities (i.e., peaks and valleys) from the mean line. R_t is defined as the height difference between the highest peak and lowest valley in the tracing length for the entire analyzed area. R_sk is the skewness and represents the degree of symmetry of the surface heights about the mean plane; the best surface has R_sk equal to 0.