LONG-DURATION METAL-ON-METAL TOTAL HIP ARTHROPLASTIES WITH LOW WEAR OF THE ARTICULATING SURFACES

The 20-year performance of metal-on-metal hip articulations has not be en reported. Five McKee-Farrar total hip prostheses and one Sivash pro sthesis were obtained at revision surgery after a mean implantation ti me of 21.3 years. A radiographic, histologic, implant, and wear analys is was performed on these total hip implants with cobalt-chrome metal- on-metal articulations. All cases were associated with femoral compone nt loosening, but the bearing surfaces performed remarkably well. The worst case estimate of combined femoral and acetabular linear wear was 4.2 mu m per year, about 25 times less than that typically seen with polyethylene. Metal particles and foreign-body inflammation were seen in all cases, but the volume of reactive tissue was small compared wit h what is generally seen at revision of hips with a polyethylene aceta bular bearing. This may be due to a reduced particle burden or a decre ased inflammatory reaction to particulate metal, or both. In addition to articular wear, other sources of metal particles included femoral n eck impingement on the acetabular rim, stem burnishing, and corrosion. Prosthetic hip reconstructions can fail for many reasons, including s uboptimal femoral stem and/or acetabular cup design and/or fixation. B y today's standards, the McKee-Farrar and Sivash stem and acetabular c omponent designs are suboptimal; however, after more than 20 years of use, the metal-on-metal bearing surfaces in these cases demonstrated l ow wear and do not appear to be the cause of failure. Recent advances in total hip arthroplasty, which include improved implant design, mate rials, manufacturing, and fixation, combined with a better understandi ng of the mechanisms of implant loosening and failure, suggest that th e cobalt-chrome metal-on-metal bearing be reexamined as an alternative to polyethylene when exceptional durability is required.