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Cup inclination linked to early increases in metal ion levels for metal resurfacing cases

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COPENHAGEN — A randomized controlled trial conducted in Denmark analyzing metal ion levels and lymphocyte counts relative to metal-on-metal hip resurfacing vs. ceramic-polyethylene total hip arthroplasty revealed increased metal ion concentrations in the metal resurfaced group during the first 8 postoperative weeks.

“We found that a small head was associated to an increased cobalt chromium ion level, and we also found the cup placement and inclination angle of 45° also had an increased ion level,” said Jeannette Penny, PhD, who presented her findings during Tribology Day at the 12th EFORT Congress 2011 here. “Actually, at this time, we could not find any difference between a regular hip replacement and a resurfacing component for any of the lymphocyte counts by themselves or their totals.”

By comparison, levels of metal ions such as as chromium (Cr) and cobalt (Co), which may be present when hip articulations are considered “worn in,” remained below 0.2 ppb in the total hip arthroplasty group. Penny and colleagues followed both groups from baseline to 1 year postoperatively. Each group consisted of 19 patients aged about 55 years to 57 years old.

In the resurfacing arthroplasty group, Co and Cr concentrations increased substantially in the first 8 weeks, followed by a slower subsequent increase through the 1-year follow-up.

Penny said that her team now has the 2-year results and longer follow-up is needed

Reference:

• Penny J, Varmarken J, Ovesen O, et al. Metal ions and lymphocyte counts in the running-in period. An RCT between resurfacing hip arthroplasty (RHA) and ceramic on poly total hip arthroplasty (THA). Paper #3442. Presented at the 12th EFORT Congress 2011. June 1-4. Copenhagen.
• Disclosure: Penny and colleagues have received government support, and institutional support from DePuy and Biomet.

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