A randomized comparison of all-polyethylene and metal-backed tibial components

Clinical failures of all-polyethylene tibial components in total knee arthroplasty generally have been failures of design, not materials. The current study was designed to compare a modern congruent all-polyethylene tibial component with a metal-backed tibial component with the same articular design and geometry. All patients older than 60 years of age requiring total knee arthroplasty were randomized prospectively to receive either a cemented posterior cruciate ligament-retaining all-polyethylene component or a metal-backed tibial component with identical articular surfaces. All patients received identical cemented femoral and all-polyethylene patellar implants. The mean age of the patients was 69 years, and the mean American Society of Anesthesiology score was 3. The diagnosis was osteoarthritis in 92% of this population. Three hundred twenty-four total knee arthroplasties in 296 patients were performed; 213 joints (111 all-polyethylene tibias and 102 metal-backed tibias) with a minimum of 3 years followup (mean, 49 months) are reported. The preoperative Knee Society knee score in the group of patients who received an all-polyethylene tibial component was 38 points, improving to 84 points at latest followup, whereas in the group of patients who received a metal-backed tibial component, the score improved from 35 to 85 points. Functional scores increased from preoperative values of 56 to 74 points in the patients who received all-polyethylene tibial components, and 57 to 72 points in the patients who received metal-backed tibial components. Range of motion measured at latest followup averaged 106 degrees in patients who received an all-polyethylene tibial component and 107 degrees in the patients who received a metal-backed component, and postoperative tibiofemoral alignment averaged 6 degrees valgus for both groups. There were 13 reoperations for instability, patellofemoral problems, or deep infection, but none for aseptic loosening or wear in either group. These differences were not statistically significant, nor were any measures of patient satisfaction or clinical outcome between the two groups in this period. Total knee arthroplasty with a well-designed, contemporary congruent all-polyethylene tibial component functions equivalently to its metal-backed tibial counterpart at 3- to 5-year followup in this patient population, and is less costly ($675).