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 th ese metal-on-metal designs than it was with metal-on-polyethylene designs. In the late 1980s, a metal-on-metal design,vith improved clearance (adequat e 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 Me tasul 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 deter mine 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 cemente d 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 pati ents (fifty-six hips) had complete clinical and radiographic data four to 6 .8 Sears after the operation, and they made up the study group. The patient s were evaluated with use of the Harris hip score, a patient-self-assessmen t form, and radiographs. Results: At an average of 5.2 years (range, four to 6.8 years) after the op eration, the average total Harris hip score for the fifty-three patients wh o did not have a revision was 89.6 points (range, 62 to 100 points). The av erage Harris pain score was 41.0 points (range, 30 to 44 points), and the a verage Harris limp score was 9.4 points (range, 5 to 11 points). One patien t had revision of a loose cup, but there were no other loose acetabular com ponents in the series. Two patients had revision of the acetabular componen t because of dislocation. No patient had a loose or revised femoral compone nt. Therefore, the mechanical failure rate was one (2 percent) of fifty-six patients. Thirty-six of forty-seven patients who completed the patient-sel f-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 ra diographs because of the metal-on-metal articulation. No hip had radiograph ic evidence of acetabular osteolysis and two hips had calcar resorption, bu t there was no other radiographic evidence of focal osteolysis. Conclusions: Our four to seven-year experience,vith this articulation surfa ce indicates that the clinical results are similar to those of total hip re placements with a metal-on-polyethylene articulation. We believe that the M etasul articulation may have a role in reducing the wear that occurs,vith t otal hip replacement. The Metasul articulation appears to be particularly i ndicated for more active patients. A historical comparison with the reports in the literature of which we are aware indicated that the hips in our stu dy had a lower rate of acetabular revision and loosening than did those wit h previous metal-on-metal designs and that they had no more acetabular loos ening or osteolysis than did those,vith metal-on-polyethylene articulations followed for an average of five Sears.