METAL ION LEVELS FOLLOWING METAL-ON-METAL TOTAL HIP REPLACEMENTS – A THIRTY YEAR FOLLOW UP STUDY

Abstract

As a result of the increased popularity of metal-on-metal bearings for total hip arthroplasty, concerns have been expressed about patient exposure to increased serum metal ion levels.

We therefore performed a retrospective review of patients with metal-on-metal, uncemented Ring total hip replacements with a minimum follow up of thirty years.

After allowing for prosthesis revision and patient mortality, 6 hips in 5 patients were reviewed and serum ion levels measured. Similar cohorts of patients with other combinations of bearings were compared with an age-matched osteoarthritic control group.

Serum cobalt and chromium levels in the metal-on-metal hip arthroplasty group were significantly higher than in all other groups and approximately five and three times greater respectively than in the group with no implants. Unlike the stainless steel-on-plastic group, the cobalt/chrome-on-plastic group showed significantly raised serum cobalt levels compared with the control group. It is of interest that patients who have had their metal-on-metal hip replacements revised to metal-on-plastic, have metal ion levels that are not statistically different to those of the osteoarthritic control group.

Though we acknowledge the small numbers of patients studied, no identifiable harmful effects were found.

We conclude that serum metal ions remain elevated throughout the life of the metal-on-metal articulation. Metal bearing hip arthroplasty is being used in ever younger patients and together with increased life expectancy we are exposing our patients to potentially harmful levels of metal ions throughout the life of the implant.