The effect of socket design, materials and liner thickness on the wear of the porous coated anatomic total hip replacement

The wear of joint replacement prostheses represents the greatest challenge to their continued development. Parameters such as polyethylene quality, liner thickness and metal backing have all been implicated as potential detractors in the search for the lowest-wearing socket. This study examined the effect of these parameters through an extensive study of the two versions of the porous coated anatomic (PCA) hip prosthesis (one-piece socket and snaplock socket). For the whole cohort the wear rate was found to be 88 (SE 10) mm³/year and the clinical wear factor was 2.00 (SE 0.28) × 10^-6 mm³/N m. When the two socket types were investigated individually, the wear factors found were 2.39 (SE 0.44) × 10^-6 mm³/N m and 0.99 (SE 0.25) × 10^-6 mm³/N m for the one-piece and snaplock, respectively. This illustrates that the metal backing per se does not predispose these sockets to rapid wear. The good wear performance of the snaplock liner may be attributed to the high quality of the ultra-high molecular weight polyethylene (UHMWPE) used and the shorter implantation period compared to that for the one-piece design. No correlation was found between the thickness of the liner and the clinical wear factor. Within the range of thicknesses tested here, UHMWPE thickness is not an influential parameter for the hip prosthesis and this is confirmed by theory.