Long-term outcome of low contact stress total knee arthroplasty with different mobile bearing designs

Purpose: to evaluate the differences in clinical outcome and survivorship of three different mobile bearings for total knee arthroplasty. Methods: a retrospective study was conducted in 60 patients (53 females, 7 males, mean age: 68 years and 5 months) each submitted to total knee replacement using one of the three different mobile bearings of the LCS system (Depuy Johnson & Johnson, Warsaw, IN). The diagnosis was knee osteoarthritis in 57 cases and rheumatoid arthritis in three cases. Three different groups of 20 cases each were identified: total knee arthroplasties with mobile menisci (group 1); total knee arthroplasties with the rotating platform (group 2); and total knee arthroplasties with the anteroposterior glide platform (group 3). As regards the component fixation, 33 implants were cementless, three were cemented, and in 24 only the tibial component was cemented. The patella was not replaced. Results: although the duration of follow-up differed between the three groups, the clinical and radiological results at final follow-up showed no revision of femoral and/or tibial components for mechanical or septic reasons, and no signs of impending failure. One meniscal bearing, showing polyethylene wear after 17 years, was successfully replaced. Conclusions: the present retrospective study confirmed the long-term effectiveness of knee implants with mobile bearings, in which the congruity of the surfaces makes it possible to overcome the problem of high contact stresses that may result in polyethylene wear and osteolysis; at the same time, these implants eliminate constraint forces thereby reducing the risk of mechanical loosening. Level of evidence: Level III, retrospective comparative study