Total hip arthroplasty with use of the Metasul metal-on-metal articulation. Four to seven-year results.

BACKGROUND: Total hip replacements with a metal-on-metal articulation were commonly used until the mid-1970s; most were then abandoned in favor of hip replacement with a metal-on-polyethylene articulation. The reason for this change was primarily early cup loosening, which was more prevalent with these metal-on-metal designs than it was with metal-on-polyethylene designs. In the late 1980s, a metal-on-metal design with improved clearance (adequate space between the femoral head and the acetabular articulation surface to allow fluid film lubrication and clearance of any debris from within this joint), metal hardness, and reproducible surfaces was introduced by Sulzer Orthopedics in Switzerland. Orthopaedic surgeons were interested in this Metasul articulation because the contribution of polyethylene wear particles to the failure of total hip replacements had become evident. This study was undertaken to review the clinical performance of this implant and to determine if early acetabular loosening or revision and wear and osteolysis were prevalent.

METHODS: Between 1991 and 1994, seventy patients (seventy hips) had a total hip replacement with the Metasul metal-on-metal articulation and a cemented Weber cup. Nine patients died less than four years after the replacement; none of these deaths were related to the operation. Five patients were not available for radiographic evaluation, but they were contacted and it was known that the hip was not painful and had not been revised. Fifty-six patients (fifty-six hips) had complete clinical and radiographic data four to 6.8 years after the operation, and they made up the study group. The patients were evaluated with use of the Harris hip score, a patient-self-assessment form, and radiographs.

RESULTS: At an average of 5.2 years (range, four to 6.8 years) after the operation, the average total Harris hip score for the fifty-three patients who did not have a revision was 89.6 points (range, 62 to 100 points). The average Harris pain score was 41.0 points (range, 30 to 44 points), and the average Harris limp score was 9.4 points (range, 5 to 11 points). One patient had revision of a loose cup, but there were no other loose acetabular components in the series. Two patients had revision of the acetabular component because of dislocation. No patient had a loose or revised femoral component. Therefore, the mechanical failure rate was one (2 percent) of fifty-six patients. Thirty-six of forty-seven patients who completed the patient-self-assessment form rated their result as excellent; seven, as very good; two, as good; one, as fair; and one, as poor. Wear could not be measured on radiographs because of the metal-on-metal articulation. No hip had radiographic evidence of acetabular osteolysis and two hips had calcar resorption, but there was no other radiographic evidence of focal osteolysis.

CONCLUSIONS: Our four to seven-year experience with this articulation surface indicates that the clinical results are similar to those of total hip replacements with a metal-on-polyethylene articulation. We believe that the Metasul articulation may have a role in reducing the wear that occurs with total hip replacement. The Metasul articulation appears to be particularly indicated for more active patients. A historical comparison with the reports in the literature of which we are aware indicated that the hips in our study had a lower rate of acetabular revision and loosening than did those with previous metal-on-metal designs and that they had no more acetabular loosening or osteolysis than did those with metal-on-polyethylene articulations followed for an average of five years.