Carbon-fibre-reinforced PEEK: An alternative material for flexion bushings of rotating hinged knee joints?

Abstract

For prosthetic knee joints of the hinged type, typically polyethylene (PE) flexion bushings are used between axis and femoral component to prevent metallic wear. Nevertheless, PE-wear can lead to periprosthetic osteolysis followed by aseptic loosening of the implant. Based on high creep and wear resistance carbon-fibre-reinforced polyether ether ketones (CFR-PEEKs) could provide an alternative material to ultra-high-molecular-weight polyethylene (UHMWPE) for this bearing type. Flexion bushings of four different materials were investigated (CFR-PEEK pitch fibres, CFR-PEEK PAN fibres, virgin PEEK without carbon fibres and UHMWPE) using a bushing tester. For determination of the polymeric and metallic wear, gravimetric measurements and particle analyses were performed. The polymeric wear rates of CFR-PEEK PAN (6.657 ± 0.714 mg/10⁶ cycles) and CFR-PEEK pitch (32.085 ± 2.748 mg/10⁶ cycles) were significantly higher compared to the polymeric wear rates of virgin PEEK (0.764 ± 0.283 mg/10⁶ cycles) or UHMWPE (-0.015 ± 0.011 mg/10⁶ cycles) (p < .001). In addition, the metallic wear rates were significantly higher when using bushings made of CFR-PEEK PAN (3.373 ± 0.214 mg/10⁶ cycles) and CFR-PEEK pitch (3.604 ± 0.355 mg/10⁶ cycles), than when using bushings made of virgin PEEK (0.177 ± 0.049 mg/10⁶ cycles) or UHMWPE (0.031 ± 0.011 mg/10⁶ cycles) (p < .001). The mean particle size of the two CFR-PEEK groups was significantly smaller compared to the virgin PEEK and UHMWPE group (p < .001). According to these results, the clinical use of CFR-PEEK in combination with CoCr could lead to higher wear rates and this should be avoided. Virgin PEEK may still be considered as an alternative to UHMWPE to use it for flexion bushings in a hinged knee joint.