Morphological assessment of in vivo wear of orthopaedic implants using multiscalar wavelets

The properties of the femoral counterface are recognised as very significant in the study of the tribological design of artificial joints and the wear of ultra-high molecular polyethylene (UHMWPE). Research has shown that morphological features of femoral counterfaces heavily interfere with the wear of UHMWPE. It has been reported that if 1–2 μm defects or deep scratches are presented in a diamond like carbon (DLC) coated head, the third-body damage can cause a 7–15-fold increase in a UHMWPE wear rate, and in a metallic surface. The typical third-body damage can be up to a 30–70-fold compared with smooth roughness surface. Therefore, the identification of morphology of counterface surfaces has become an important requirement in the field of wear and tribology of the hip joint system. This paper proposes a methodology for a multiscalar wavelet for addressing morphological surfaces in order to extract the significant elements of 3D bearing surfaces of orthopaedic implants. The multiscalar wavelet is used to decompose a surface signal into the scalar domain. In wavelet analysis, the Cartesian space-based information is transferred into scale-based information, which provides not only the frequency events of the original signal but also keeps their location properties; as a result, morphological features can be identified. A series of ceramic, metallic and DLC femoral heads in vivo wear have been used to demonstrate the applicability of using the multiscalar wavelet model in the assessment of the morphology of these surfaces.