セラミック製LFA人工膝関節の有用性と将来性

抄録

Ceramic total knee arthroplasty was introduced as a new-generation knee prosthesis in clinical practice; it was expected to reduce polyethylene wear due to its resistance to abrasion and good lubrication characteristics. We developed a posterior cruciate ligament (PCL)-retaining total knee system (LFA-I, Kyocera, Japan) composed of an alumina ceramic femoral component and a titanium-alloy tibial component in 1992. Wear testing using a knee joint simulator revealed that the maximum depth of wear was about one-fifth of that of a knee prosthesis made of cobalt-chromium alloy after 1 million simulated gait cycles. Advances in ceramics technology allowed us to use zirconia, which is a tougher ceramic material than alumina, and we developed the zirconia-ceramic LFA-III total knee system in 1999. The thickness of the zirconia ceramic femoral component is almost the same as that of the commonly used metal component. Subsequently, we developed the PCL-substituting zirconia-ceramic LFA-III total knee system in 2002. The mid- to long-term clinical results of these prostheses have been encouraging. The possibility of failure of a ceramic component is a valid concern; however, this phenomenon has yet to be reported. In addition to their wear advantages, these prostheses have other superior features over cobalt-chromium prostheses. Allergic reactions to the metal ions released by metallic components have been reported, and this phenomenon is an emerging issue; however, ceramic is totally inert and thus can avoid the potential allergy problems of metal ions. In addition, an alumina ceramic femoral component makes it possible to precisely analyze the periprosthetic tissue with computed tomography scans without encountering beam-hardening artifacts. Furthermore, magnetic resonance imaging scans can be safely carried out to evaluate bone and soft tissue around a knee with a ceramic component. The superiority of the ceramic prosthesis with respect to in vivo wear has not been proven; however, no long-term failure associated with wear has been reported in patients with the LFA total knee system. This article reviews clinical outcomes with the LFA total knee system and evaluates the role of ceramic implants in total knee arthroplasty.