METAL ION RELEASE FOLLOWING FORGED, HIGH CARBON CONTENT, METAL-ON-METAL HIP SURFACE REPLACEMENT ARTHROPLASTY

Abstract

INTRODUCTION: Improved factors influencing component wear with regards to bearing surfaces, metallurgy, tribology, and manufacturing technology allowed reintroduction of metal-on-metal (MOM) articulation in total hip arthroplasty (THA) and surface replacement arthroplasty (SRA).

MATERIALS AND METHODS: Sixty three patients were implanted with a forged, high carbon content, chrome-cobalt, MOM SRA component (Durom, Zimmer, USA). Samples of whole blood and serum were collected pre-operatively and, post-operatively at three months, six months one year and two years. Chromium and cobalt concentrations were measured using a a high-resolution, sector-field, inductively-coupled plasma mass spectrophotometer (HR-SF-ICP-MS).

RESULTS: At two years, whole blood levels were Cr 1.25 umol/L (SD 0.55), Co 0.62 umol/L (SD 0.26). In comparison to the pre-operative levels, the levels increased significantly for both elements Cr 1.3X, Co 5.0 X. Component size was inversely proportional to the chromium and cobalt ion levels at one year post operatively (ANOVA regression analysis, p = 0.0404, for Co and p = 0.0156 for Cr). Other factors such as age and activity level did not correlate with the metal ions levels.

DISCUSSION AND CONCLUSION: Chromium and cobalt metal ions measured in patients following implantation of the high carbon content, forged, metal on metal SRA implants used in this study are very low in comparison to other published results with different SRA implants. We believe that these encouraging results found with the SRA components used are resultant of favourable manufacturing and tribologic factors such as low surface roughness, high carbon content, forged chromium and cobalt material, component clearance, and optimum component sphericity. The results of this study are also in accordance with the concepts of reduced wear with larger diameter MOM articulations.