3D linear and volumetric wear measurement on artificial hip joints—Validation of a new methodology

Artificial hip replacement joints have been in use to treat osteoarthritis and rheumatoid arthritis for decades. These devices consist of a metallic/ceramic ball articulating against a polyethylene or metallic/ceramic hemispherical cup. However, these artificial joints do wear and their clinical performance starts declining after 10–20 years of successful use. In the case of hard-on-hard bearings, the wear depth and volume remain very small and their measurement has remained a challenge to current technologies.A novel device, the non-contact RedLux Artificial Hip Profiler, which is based on the chromatically encoded confocal measurement method, has been developed so that these joints can be measured accurately, reproducibly and in a short timescale. The system outputs the component radius for the unworn part, the linear depth of wear and also provides the wear volume.The design principles are presented and the capability of the equipment to measure worn parts, with linear wear between a few microns and tens of microns is hereby characterised, and correlated with laser micrometer diameter measurements, roundness measurements of linear wear and gravimetric wear assessment.The Artificial Hip Profiler is capable of measuring spherical bearing surfaces with a resolution of 20 nm. The correlation to benchmark methods for the three parameters considered is very high, with correlation coefficients of 1.02 and 0.95 for the linear and volumetric wear, respectively. The R values were 0.988 and 0.996, respectively.