Yet another study is pointing to potential dangers posed by metal-on-metal hip implants. This time, an article published in the Journal of Arthroplasty is reporting corrosion in the head taper junction was more likely to occur in patients with 36-mm diameter metal-on-metal hip replacement, compared to those with the same size metal-on-polyethylene device. Corroded all-metal hip implants were also associated with adverse local tissue reactions, the study found.
Metal-on-Metal Hip Implant Concerns
It is believed that all-metal hip replacements, which consist of a metal acetabular cup and metal femoral head, can shed minute particles of cobalt and chromium into surrounding tissue, and even into a patient’s blood stream. This can result in a condition called metallosis, which causes the death of tissue around the implant, including bone and muscle. Metal ions can also cause irreversible damage to DNA in cells, and have been found in many organs following hip replacements, including marrow, blood, liver, kidneys and bladder.
Metal-on-metal hip implants have been the subject of safety concerns since the August 2010 global recall of DePuy Orthopaedic’s ASR hip implants. In May of last year, the U.S. Food & Drug Administration (FDA) asked 21 makers of metal-on-metal hip implants to conduct safety studies of their devices. In June, the agency will convene a panel of outside advisers to discuss the problems related to metal-on-metal hip replacements. Since then, several studies, including recent reports in The Lancet and the British Medical Journal, have linked metal-on-metal hip implants to premature failure. The authors of The Lancet study went so far as to call for an end to the use of the devices, while the British Medical Journal report warned that hundreds of thousands of people around the world may have been exposed to dangerously high levels of toxic and potentially cancer-causing metals from failing metal-on-metal hip implants.
Journal of Arthroplasty Study
For the new Journal of Arthroplasty Study, researchers evaluated taper corrosion in 36-mm diameter metal-on-metal and metal-on-polyethylene femoral heads from a single manufacturer retrieved for various reasons. The taper corrosion on 19 all-metal heads and 14 metal-on-polyethylene heads was visually graded on a 5-point scale. The grading revealed:
- A total of 8 all-metal heads (42%), compared to only 1 metal-on-polyethylene head (7%), demonstrated corrosion outside of the taper zone.
- Metal-on-metal patients who had undergone revisions secondary to adverse local tissue reactions had greater corrosion scores than patients without reactions.
- Adverse local tissue reactions in metal-on-metal hip replacements were also likely to exhibit corrosion outside of the taper junction.
- The corrosion score increased with implantation time, and at all time intervals, the corrosion score for the all-metal group was greater.
Because corrosion worsens with time, the study authors voiced concern that metal-on-metal hip implant failures due to adverse local tissue reactions will increase with longer follow-up.