This review paper by Gioe and Maheshwari focuses on the all-polyethylene tibial component in total knee arthroplasty. The history of the all-polyethylene tibial component design starts with the earliest total knee replacement devices and extends to the present day. Evaluation of the all-polyethylene component remains very important, as it has the potential to deliver equal or superior quality in implant performance at a lower cost to the health care system. Thus, the importance of this topic in knee arthroplasty cannot be overstated. The relative effectiveness of the all-polyethylene device compared with modular components is a function of design optimization, polyethylene structural and wear properties, and the unique challenges associated with modular components.
The reader should take note in the section on the historical aspects of knee implant design that failure of the early polyethylene tibial components led ultimately to the development of metal-backed tibial components. The duo-condylar prosthesis, for example, had an all-polyethylene tibial component that offered only two sizes when introduced into the marketplace. In retrospect, one must conclude that the failures in the initial attempts to use polyethylene stem as much from the lack of material thickness, tibial surface coverage, and instrumentation as from any intrinsic problem related to the substrate polyethylene material. Indeed, some of the earliest all-polyethylene tibial components performed quite well when compression molded, implanted in proper alignment, and used with adequate material thickness to withstand joint-loading.
Like many innovations in orthopaedic surgery, the initial enthusiasm for metal backing and modularity in relation to the modeling of stresses and strains at interfaces becomes tempered by clinical experience with unanticipated failure mechanisms. The adoption of modular metal-backed tibial components was driven by the potential for more uniform load transfer and intraoperative flexibility with regard to exchanging liners. The unanticipated outcome was that surgeons would rarely take advantage of the modular feature, and movement of the modular polyethylene insert upon the metal tibial tray created an increased burden of polyethylene debris. Likewise, as improvements in the congruity and wear properties of the polyethylene for both cruciate-sparing and cruciate-substituting designs have been made available in the form of modular components, the all-polyethylene tibial component has kept pace with all of the changes.
The authors point out that cementless fixation may limit the long-term applicability of the all-polyethylene tibial component. However, until a monoblock metal-backed tibial insert demonstrates equal performance, there is little reason not to use cement and polyethylene without metal backing. Cemented fixation has proven to be quite durable, predictable, and cost-effective in total knee replacement. In particular, the economic analysis presented in the manuscript is quite compelling. With margins for arthroplasty operations being quite thin for hospitals under the best of circumstances, a savings of more than $600.00 per case could certainly help to tip the balance toward the all-polyethylene choice as long as a high-quality outcome does not have to be sacrificed. In fact, the authors make the case that the largest and longest clinical reports on the all-polyethylene tibial component are just as favorable as those reported for any other design.
In summary, the authors make a compelling case for use of the all-polyethylene tibial component under most clinical circumstances. Only new technology or new data from the third decade of use could possibly detract from the observation that the all-polyethylene tibial component performs as well as any component available for primary joint replacement and at a lesser cost than that of a modular device.
*The author did not receive any outside funding or grants in support of his research for or preparation of this work. The author, or a member of his immediate family, received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (DePuy)