The rationale for metal-on-metal total hip arthroplasty

Metal-on-metal total hip arthroplasty has the longest clinical history of any of the currently used articular couples. Longterm followup of what are now considered suboptimal designs (eg, McKee Farrar, Ring, Sivash) has produced a wealth of knowledge regarding the safety and efficacy of this articular combination. Retrieval analysis of metal-on-metal total hip arthroplasty articular couples has shown wear between 1 and 5 microns per year after initial wear-in, in comparison with 100 to 200 microns per year associated with metal-on-polyethylene wear. The constituent metal ions released through wear of the metal-on-metal total hip arthroplasty are excreted primarily in the urine; serum levels have been 3 to 5 times higher in patients who have had metal-on-metal total hip arthroplasties than in control subjects. No adverse physiologic effects have been identified in the long-term followup of patients exposed to cobalt-chromium implants. The clinical results of metal-on-metal total hip arthroplasties equal or exceed those of conventional articular couples and rarely are associated with osteolysis compared with conventional couples. Additional advantages of the metal-on-metal combination are the ability to use larger-diameter femoral heads for enhanced stability and the absence of concern over possible fracture of the articular components. The long-term experiences with metal-on-metal total hip arthroplasty make this combination of implant material the conservative choice for success.