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Saturday, March 13, 2004

Metal-on-metal hip replacement risk factors identified

By Mary Ann Porucznik

Researchers for Scientific Exhibit SE021, "Metal-on-metal hybrid surface arthoplasty of the hip: Clinical results and risk factors for failure," report that tribology, biocompatibility studies, improvement of design and surgical technique combine to achieve successful medium-term results for metal-on-metal surface arthroplasty (MMSA) of the hip.

The study reviewed 400 hips in 355 patients who received a hybrid MMSA at a single institution. The average age of patients was 48 years; 73 percent of the study group were male. Investigators analyzed data such as femoral head cysts, activity, patient weight, previous hip surgery and femoral component sizes. Failed components were retrieved, sectioned and analyzed histologically. A surface arthroplasty risk index (SARI) was developed for patient selection.

The study group had a mean follow-up of 4.6 years (range: 3.2 to 7.2 years) with excellent clinical results. There were 15 revisions: three neck fractures, nine femoral loosenings and one case each of postoperative acetabular component protrusio, sepsis and recurrent subluxation. The four-year survivorship was 94.4 percent.

The most important risk factors for femoral loosening were large cyst formation (p = 0.029), height (p = 0.032), female gender (p = 0.005) and smaller component size in male patients (p = 0.005). Patients with a SARI greater than 3.0 were 4.2 times more at risk of early failure than those who had a SARI less than 3.0. Implant survival among the higher-risk patients was 89 percent, compared to a 97 percent survivorship among lower-risk patients. No metallosis was observed in retrieved specimens and wear was not measurable by Coordinate Measurement Machine (CMM).

Investigators note that bone preparation and fixation are paramount to prevent femoral failures. Cementing the metaphyseal stem and reducting impact activities improves the outlook for young patients with risk factors.

The research team was headed by Harlan C. Amstutz, MD, and included Paul E. Beaule, MD, Frederick Dorey, PhD, Harry McKellop, PhD, and Patricia A. Campbell, all of Los Angeles; Michael J. Le Duff, MA, of Glendale, Calif., and Thomas A. Gruen, MS, of Wesley Chapel, Fla. Research funding was provided by Wright Medical Technology and the Los Angeles Orthopaedic Hospital Foundation.

  Preoperative anteroposterior view of a 60-year-old former professional tennis player with osteoarthritis.
  Intraoperative photograph showing the femoral head after preparation. There is excellent cancellous trabecular bone for acrylic fixation and additional fixation holes were not utilized in this early surgery.
  This section of the surface arthroplasty in a 53-year-old man with DDH that failed after five months shows a 6-mm to 8-mm layer of bone cement in the done superior area and uncovered reamed bone inferiorly at the component edge. Note the fracture through this area.
  Example of a femoral radiolucency in all three zones around the metaphyseal stem in a 28-year-old man, 3.5 years after metal-on-metal surface arthroplasty. The patient denies having any pain at last follow-up and remains very active (UCLA activity score 10).
  Graph showing wear over time of 12 44-mm ConservePlus prostheses in a hip simulator. Note the wear-in period during the first half-million cycles and the extremely low wear of the subsequent steady state phase.

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Last modified 20/February/2004