Mobile-bearing knee replacements have been implanted for more than 20 years. The Oxford unicompartmental replacement and the LCS (low contact stress) total knee system have been studied extensively. Ninety-five to 97% 10-year survivorship rates of the Oxford unicompartmental replacement have been reported. Low contact stress meniscal-bearing survivorship rates of 98% at 6 years and 94.6% at 8 years have been reported. Ninety-five to 100% survivorship rates at the 11-and 12-year followup have been reported for low contact stress rotating platform knee replacements. Complications with the Oxford unicompartmental replacement include an increase in bearing dislocation and an increase in loosening rate when the components were placed in knees that had anterior cruciate ligament deficiency. Complications with the low contact stress total knee system include bearing dislocation (meniscal, rotating platform, and patellar), bearing breakage, and polyethylene wear. If mobile-bearing knee replacements are inserted with the same precision as fixedbearing knee replacements, the results should at least be comparable. There may be some potential for an increase in durability, compared with fixed-bearing knee replacements, especially those of a modular design.