The mechanical response of a polyetheretherketone femoral knee implant under a deep squatting loading condition

Abstract

The current study was designed to investigate the mechanical response of a polyetheretherketone-on-polyethylene total knee replacement device during a deep squat. Application of this high-demand loading condition can identify weaknesses of the polyetheretherketone relative to cobalt-chromium. This study investigated whether the implant is strong enough for this type of loading, whether cement stresses are considerably changed and whether a polyetheretherketone femoral component is likely to lead to reduced periprosthetic bone loss as compared to a cobalt-chromium component. A finite element model of a total knee arthroplasty subjected to a deep squat loading condition, which was previously published, was adapted with an alternative total knee arthroplasty design made of either polyetheretherketone or cobalt-chromium. The maximum tensile and compressive stresses within the implant and cement mantle were analysed against their yield and fatigue stress levels. The amount of stress shielding within the bone was compared between the polyetheretherketone and cobalt-chromium cases. Relative to its material strength, tensile peak stresses were higher in the cobalt-chromium implant; compressive peak stresses were higher in the polyetheretherketone implant. The stress patterns differed substantially between polyetheretherketone and cobalt-chromium. The tensile stresses in the cement mantle supporting the polyetheretherketone implant were up to 33% lower than with the cobalt-chromium component, but twice as high for compression. Stress shielding was reduced to a median of 1% for the polyetheretherketone implant versus 56% for the cobalt-chromium implant. Both the polyetheretherketone implant and the underlying cement mantle should be able to cope with the stress levels present during a deep squat. Relative to the cobalt-chromium component, stress shielding of the periprosthetic femur was substantially less with a polyetheretherketone femoral component.

The Effects of Cyclic Loading and Motion on the Implant–Cement Interface and Cement Mantle of PEEK and Cobalt–Chromium Femoral Total Knee Arthroplasty Implants: A Preliminary Study

“…It is postulated that the higher stiffness of CoCr compared to PEEK also gives the potential for higher local stresses in the cement–CoCr implant interface as the femoral component is less compliant. Previous studies have shown the stiff CoCr component to generate high stress peaks in the cement underneath the proximal anterior flange [ 24 , 25 , 26 , 37 ]. Many small cracks were visible in this region.…”

“…Many small cracks were visible in this region. Analysis of these small cracks was beyond the scope of this study but there is potential for these small cracks to grow, which may further increase cement damage in the anterior flange [ 20 , 24 , 25 ]. The numbers of cracks in cement at the anterior flange and posterior chamfer areas of the cement mantle were similar in both implants; however, there was a greater number of cracks in the PEEK–cement interface in the anterior chamfer and the posterior flange compared to the CoCr–cement interface.…”

“…In addition, the simulator included only tibiofemoral contact. When both the tibiofemoral and patellofemoral joints are considered, in vivo forces are higher, since patellofemoral contact is a major contributor to the total loads on the femoral component particularly at higher flexion angles [ 24 ]. However, the increased forces due to patellofemoral contact do not necessarily lead to an increased risk of debonding.…”

“…An increasing interest in the investigation of different materials and manufacturing techniques for joint replacements however brings about the potential for different failure modes of the implant. PEEK-OPTIMA™, for example, has been considered as an alternative to CoCr in the femoral component of a TKA to give a metal-free implant [ 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. The lower modulus of a PEEK implant compared to CoCr may help to reduce stress shielding but may also change the distribution of forces at the cement–implant interface, which may influence implant fixation.…”

Statistical Modeling of Lower Limb Kinetics During Deep Squat and Forward Lunge

“…For the purpose of implant wear testing, implant fixation, and joint stability analysis, there are other more challenging activities commonly performed in daily living that might be of particular interest (Hartmann et al, 2013). Clinical, experimental, and computational studies have clearly reported increased complication risk and wear rate under high contact stress conditions (Kang et al, 2008;O'Brien et al, 2015;de Ruiter et al, 2017).…”