A Comparison in Proximal Tibial Strain Between Metal-Backed and All-Polyethylene Anatomic Graduated Component Total Knee Arthroplasty Tibial Components

https://doi.org/10.1016/j.arth.2009.06.018Get rights and content

Abstract

Loading in total knee arthroplasty (TKA) is multifactorial and dependent on alignment, ligament balance, patient, and implant factors. Abnormal loading has been linked to clinical failure; however, the respective contribution of each factor to failure is not well known. This study defined the effect of metal backing on loading patterns in the proximal tibia. Composite tibiae were implanted with metal-backed and all-polyethylene Anatomic Graduated Component TKA tibial components (Biomet, Inc, Warsaw, Ind) and coated with photoelastic material allowing full-field dynamic strain quantification. In simulated varus loading distributions, significant increases in measured strain were observed ranging from 40% to 587% for all-polyethylene vs metal-backed tibial components. Higher observed strains in the proximal tibia observed with all-polyethylene tibial components could possibly explain increased clinical failure rates observed with this TKA design.

Section snippets

Materials and Methods

Metal-backed and all-polyethylene AGC Total Knee Systems were used in this study. Sawbones Third Generation composite tibiae (Pacific Research Laboratories, Inc, Vashon, Wash) designed to replicate the mechanical properties of cadaveric bone were chosen as test specimens to minimize interspecimen sizing and bone density variability [9]. Five left tibiae for each prosthesis type were implanted by a board-certified orthopedic surgeon 5 mm below the joint line with 75-mm-sized AGC tibial

Results

Least square means of shear strain values in each of the 24 measurement regions on the proximal tibia are reported for the 50:50 and 80:20 loading distributions in Table 1, Table 2, respectively. In this study, there were no measurement regions in any experimental group or loading condition that showed statistically significant higher shear strains in the metal-backed implanted tibiae when compared to the all-polyethylene implanted tibiae (Fig. 4, Fig. 5). The highest values of shear strain

Discussion

We have previously reported a 98% fifteen-year survival rate with the nonmodular metal-backed AGC total knee prosthesis, in a study of 4583 knees, whereas we found only a 68% ten-year survival rate in a study 536 knees with AGC all-polyethylene tibial components 4, 5. Taylor et al [13] hypothesized that excessive stresses in the proximal tibia could lead to prosthesis migration and cancellous bone failure, which is the most common failure mechanism observed for AGC all-polyethylene implants. [4]

References (17)

There are more references available in the full text version of this article.

Cited by (19)

  • Unicompartmental Knee Arthroplasty: US and Global Perspectives

    2020, Orthopedic Clinics of North America
    Citation Excerpt :

    In a randomized trial between all-polyethylene and metal-backed tibial trays, the all-polyethylene design had a 37% incidence of aseptic loosening.64 This may be attributed to the more focal tibial loading seen in these designs.65 Surgeons must be cautious of interpreting all radiolucencies as aseptic loosening, which is discussed below.

  • Analysis of an early intervention distal femoral resurfacing implant for medial osteoarthritis

    2016, Journal of Biomechanics
    Citation Excerpt :

    Nevertheless, this has not always applied to total knees where no differences in loosening have been noted between all-plastic and metal-backed in the long term in some series (Doran et al., 2015). Higher stresses have also been measured on the surface of the proximal tibia when comparing all-poly with metal-backed components (Small et al., 2010). It is not easy to reconcile those results with the finite element data however because with all-plastic, the higher interface stresses and strains are restricted to the central region rather than around the periphery.

  • Metal Backing Significantly Decreases Tibial Strains in a Medial Unicompartmental Knee Arthroplasty Model

    2011, Journal of Arthroplasty
    Citation Excerpt :

    The early mean time to failure seems to suggest mechanical factors to be significant contributors in these specific failure mechanisms in both TKA and UKA. Separate studies have correlated the presence of metal backing with improve tibial loading distribution in TKA [18,26]. The current study evaluated the bony loading response of the medial tibial beneath the operative condyle in UKA.

View all citing articles on Scopus

No benefits or funds were received in support of the study.

View full text