Mobile- vs. fixed-bearing total knee replacement: A randomized radiostereometric and bone mineral density study

BACKGROUND AND PURPOSE: It is unclear whether mobile-bearing (MB) total knee arthroplasties reduce the risk of tibial component loosening compared to fixed-bearing (FB) designs. This randomized study investigated implant migration, periprosthetic bone mineral density (BMD), and patient-reported outcomes (Oxford knee score)—all at 2 years—for the P.F.C. Sigma Cruciate Retaining total knee arthroplasty. PATIENTS AND METHODS: 50 osteoarthritis patients were allocated to either FB or MB tibial articulation. RESULTSAND INTERPRETATION: At 2 years, the mean total translation (implant migration) was higher for the FB implant (0.30 mm, SD 0.22) than for the MB implant (0.17 mm, SD 0.09) (p = 0.04). BMD decreased between baseline and 1-year follow-up. At 2-year follow-up, BMD was close to the baseline level. The knee scores of both groups improved equally well. The FB tibial implant migrated more than the MB, but this was not clinically significant. The mobile polyethylene presumably partly absorbs the force transmitted to the metal tibial tray, thereby reducing micromotion.