Metal transfer and surface roughness in ceramic femoral heads: recent investigations and future research trends

Wear of hip prostheses often occurs in vivo and represents a significant clinical problem. In revision arthroplasty of the hip, metallic deposits are frequently found on femoral heads after dislocation or repositioning in total hip arthroplasties (THA) with metal back acetabular components. The Metal Transfer (MT) phenomenon on femoral heads in THA appears as dark metallic on ceramic femoral heads and, actually, represents a very interesting research topic in the field of the biotribology, since it is strictly connected with lubrication and wear phenomena of the prostheses. Therefore, a great concern was dedicated to the analysis of the surface roughness parameters that can best reveal the tribological behaviour of these bio-bearings. In this work the Authors present the results of their recent researches developed by a cooperation of the Department of Industrial Engineering of the University of Salerno and the Rizzoli Orthopaedic Institute, furthermore discussing on future researches trends. It was investigated whether MT changed the surface roughness of the ceramic/composites femoral heads, validated a new protocol to measure surface roughness on retrieved femoral heads, analysed whether these changes were associated to the zirconia phase transformation and looked for a correlation of MT with the implants follow-up. Metal transfer was observed on all the analysed femoral heads and determined a worsening of all roughness parameters. An increase in surface roughness, as a result of transferred metal debris, could explain the cases of excessive wear.