In vitro simulation of contact fatigue damage found in ultra-high molecular weight polyethylene components of knee prostheses

Abstract

An in vitro simulation of fatigue loading of ultra-high molecular weight polyethylene (UHMWPE) knee components was carried out on a knee simulator and on a rolling and sliding wear tester. Tibial components for the knee simulator were gamma-sterilized, implantable components taken from manufacturing inventory. The rolling/sliding UHMWPE discs were machined from bar stock and either gamma sterilized in air and accelerated aged, or left as non-sterilized (controls). Cracking and delamination of samples that had been gamma sterilized in air and aged were observed in both types of tests. Contact fatigue damage was visible in as few as 150,000 cycles using the knee simulator at loads of 122 N (275 1b). The rolling/sliding samples showed signs of damage in as few as 130,000 cycles with an estimated stress of 15 MPa and 25 per cent sliding. However, cracking and delamination were not generated in the never-sterilized or recently sterilized controls. UHMWPE that has been gamma sterilized in air and aged is shown to be susceptible to contact fatigue damage. These results are important to the interpretation of in vitro total knee replacement simulations used to assess the performance of tibial bearings.

Analysis of wear asymmetry in a series of 94 retrieved polyethylene tibial bearings

“…Cracking within the bulk of the bearing material was frequently associated with areas of edge loading. This cracking, even if initially confined within the material, would be expected to result in rapid delamination under continued loading (Currier et al, 1998;Kennedy et al, 2000). In considering the frequency of edge loading in the anterior zones (1 and 2), the higher incidence of forward edge loading on the medial margin (9% versus 3%) indicates that internal rotation of the tibia is more predominant than exterior rotation of the tibia.…”

“…Laboratory investigations have measured the stress distribution across the bearing surface (Andriacchi, 1994;Morrison, 1970;Postak et al, 1997;Schipplein and Andriacchi, 1991) and have modeled of the stresses within polyethylene knee bearings (Bartel et al, 1986;Collier et al, 1991;Wright et al, 1989). Wear simulators have been used to study the mechanisms of polyethylene wear in tibial bearing inserts, and have focused on the contact fatigue failure mechanism that is critical in the rolling and sliding articulation of the knee (Blunn et al, 1991;Currier et al, 1998;Feehan, 1990;Kennedy et al, 2000;Walker et al, 1996). A number of recent investigations have quantified the surface area of wear and the volume of wear in knee bearings under various gait pattern inputs in knee simulators (Bell et al, 2003;Conditt et al, 2003;Harman et al, 2001;Laurent et al, 2003;Muratoglu et al, 2003).…”

Experimental analysis of tribological behavior of UHMWPE against AISI420C and against TiAl6V4 alloy under dry and lubricated conditions

“…It is acknowledged that the total knee joint replacements (TKRs) are very complex in their design; they could be designed to resist mechanical stress and fatigue effect due to the normal load applied in a large number of cycles during the gait and during the other activities in the common life. Ultra high molecular weight polyethylene (UHMWPE) tibial bearings articulating against metal or femoral condylar components remain the materials of choice in TKR [8][9][10][11]. Due to the functionality of the knee joint, the femoral component must rub against the surface of the tibial insert thus creating friction and wear.…”

In Vivo Oxidation Contributes to Delamination but not Pitting in Polyethylene Components for Total Knee Arthroplasty

“…In the knee, fatigue wear mechanisms are thought to predominate because of the lower conformity and higher contact stresses between the femoral and tibial components [7–8]. Thus, the consensus is that the delamination and pitting damage often observed in retrieved polyethylene tibial inserts are due to fatigue wear [8–11]. Although factors such as poor consolidation, fusion defects, and implant thickness are known to exacerbate fatigue wear in tibial inserts [7–8, 12–16], post-irradiation oxidation during shelf storage in air was ultimately recognized as probably the most important contributor to premature delamination in gamma radiation air sterilized tibial components [17–23].…”