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Debate continues over metal-on-metal vs. metal-on-polyethylene bearings in THA

Matched case-controlled study finds only slight difference in risk of loosening.

Issue: Issue 3 2004

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In a large matched case-controlled investigation, metal-on-metal bearings in total hip arthroplasty prostheses showed a decreased risk of component loosening when compared to metal-on-polyethylene surfaces; however, these differences were not statistically significant.

Douglas Naudie, MD, of the Anderson Orthopaedic Research Institute in Arlington, U.S.A. presented the investigation with the hypothesis that metal-on-metal bearing surfaces would decrease the risk of loosening, to the the American Academy of Orthopaedic Surgeons 71st Annual Meeting. “With this cohort of patients, metal-on-metal bearings demonstrated a lower risk of cup or stem loosening and stem or cup loosening alone than metal-polyethylene bearings. This was in contrast to our hypothesis, for this risk reduction was not statistically significant.”

Large European database

The investigation compared selected cases from the computerized joint registry database of the Maurice E. Müeller Research Center for Orthopaedic Surgery in Berne, Switzerland, which contains data on more than 58,000 total hip arthroplasties (THAs). According to Naudie, the patients had primary hip arthroplasty using a second generation, metal-on-metal or metal-on-polyethylene bearings. Patients were included if they had had a revision or radiographic loosening of the stem acetabular component or both.

These patients were compared with control patients who had undergone THA with similar bearing prostheses but did not experience loosening. Both groups were matched by gender, age, diagnosis, the hospital where the surgery was performed, date of surgery, length of follow-up, femoral head size, femoral stem size and the acetabular design.

Overall, 412 cases and 1268 controls were matched. Metal-on-metal bearings were present in 14.1% of cases and 19.4% of controls. Metal-on-polyethylene surfaces were used in 85.9% of cases and 80.6% of controls.

Using a conditional logistic model, the researchers found a slight decrease in the odds ratio for the metal-to-metal bearings for stem and or cup loosening and individual stem or cup loosening; however, none of the differences were deemed statistically significant.

For more information:

• Naudie D, Roeder CP, Parvizi J, et al. Metal-on-metal vs. metal-on-polyethylene bearings in hip arthroplasty: a matched case-control study. #096. Presented at the American Academy of Orthopaedic Surgeons 71st Annual Meeting. March 10-14, 2004. San Francisco.