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General Orthopaedics

CARBON FIBRE-REINFORCED PEEK AS BIOMATERIAL IN A ROTATING HINGE KNEE DESIGN: BIOTRIBOLOGICAL TESTING IN COMPARISON WITH RETRIEVAL FINDINGS

The New Zealand Orthopaedic Association and the Australian Orthopaedic Association (NZOA AOA) Combined Annual Scientific Meeting, Christchurch, New Zealand, 31 October – 3 November 2022. Part 2 of 2.



Abstract

Total knee arthroplasty with a rotating hinge knee with carbon-fibre-reinforced (CFR)-PEEK as an alternative bushing material with enhanced creep, wear and fatigue behaviour has been clinically established [1-4]. The objective of our study was to compare results from in vitro biotribological characterisation to ex vivo findings on a retrievals.

A modified in vitro wear simulation based on ISO 14243-1 was performed for 5 million cycles on rotating hinge knee (RHK) designs (EnduRo®) out of cobalt-chromium and ZrN-multilayer ceramic coating. The rotational & flexion axles-bushings and the flanges are made of CFR-PEEK with 30% polyacrylonitrile fibre content.

Analysis of 12 retrieved EnduRo® RHK systems in cobalt-chromium and ZrN-multilayer in regard to loosening torques, microscopic surface analysis, distinction between different wear modes and classification with a modified HOOD-score has been performed.

For the RHK design with the polyethylene gliding surface and bushings and flanges made out of CFR-PEEK, a cumulative volumetric wear was measured to be 12.9±3.95 mm3 in articulation to cobalt-chromium and 1.3±0.21 mm3 to ZrN-multilayer coating - a significant 9.9-fold decrease (p=0.0072).

For the CFR-PEEK flexion bushing and flanges the volumetric wear rates were 2.3±0.48 mm3/million cycles (cobalt-chromium) and 0.21±0.02 mm3/million cycles (ZrN-multilayer) (p=0.0016). The 5 million cycles of in vitro wear testing reflect a mean in vivo service life of 2.9 years, which is in accordance to the time in vivo of 12–60 months of the retrieved RHK components [5]. The main wear modes were comparable between retrievals and in vitro specimens, whereby the size of affected area on the retrieved components showed a higher variation.

For the EnduRo® RHK design the findings on retrieved implants demonstrate the high suitability of CFR-PEEK as a biomaterial for highly loaded bearings, such as RHK bushings and flanges in articulation to cobalt-chromium and to a ZrN-multilayer coating.


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