The influence of femoral head surface roughness on the wear of ultrahigh molecular weight polyethylene sockets in cementless total hip replacement

A theoretical relationship was recently proposed relating the wear behavior of polymetric bearing materials articulating against hard counterfaces.(1) This model attempts to predict the influence of surface roughness on wear. Laboratory-based studies have been used to establish the validity of these relationships, but their application to the clinical situation has not bee n investigated fully, Forty-two retrieved PCA hip joints have been assessed . The total wear volume was calculated from the penetration measured using the shadowgraph method, and roughness of the articulating surfaces was reco rded using noncontacting profilometry. The roughness of the explanted femor al heads was observed to increase (median S-a - 10.35 nm worn region, 3.05 nm peripheral region), while that of the acetabular liner fell dramatically (median S-a - 41 nn worn region, 212 nm unworn region). No evidence of a r elationship between the topography of the worn regions of the femoral head and that of the acetabular liner could be found. Similarly, the strength of the association between the surface roughness and the clinical wear factor was considerably poorer than that achieved in laboratory experiments. A nu mber of reasons for this observation are proposed, Most deleterious was con sidered to be the inability of the roughness parameters to describe the dam aging features of the surface adequately. Uncertainty as to when the surfac e of the component degrades during its life serves to introduce further dou bt as to the application of the wear models in the clinical environment. In conclusion, this study fails to provide clinical evidence to substantiate the relationship between surface finish and wear rate, The adoption of stan dardized measurement parameters and techniques would facilitate the direct comparison of joint types and the selection of the most advantageous materi als. (C) 1999 John Wiley & Sons, Inc.