Abstract
Introduction
Wear debris induced osteolysis and loosening continue to cause clinical failure in total knee replacement (TKR). To improve longevity and reduce wear alternative materials have been examined. Carbon-fibre-reinforced poly–ether-ether-ketone (CFR-PEEK) has shown promising results in wear studies [1–2].
The aim of this study was to explore the use of CFR-PEEK and PEEK as alternative bearing materials for polyethylene in TKR through experimental knee joint wear simulation.
Methods
Two novel materials were studied as an alternative to polyethylene as the tibial bearing surface in a TKR configuration using a Cobalt chrome femoral bearing in current clinical use. Six right Sigma CR fixed bearing TKRs (DePuy Synthes, UK) were paired with either PEEK or CFR-PEEK custom-made flat inserts (Invibio, UK) in a Prosim knee simulator (Simulator Solutions, UK). The tibial inserts were 14mm thick, to give an equivalent thickness to existing insert designs. A flat geometry was selected as this has previously been shown to yield low wear in polyethylene bearings [3]. The tests were conducted under High Kinematics, with anterior-posterior and internal-external displacement control [4]. Tests were conducted for three million cycles, lubricated with 25% bovine serum, with wear assessed gravimetrically at 1 and 3Mc.
Images of the wear scars were recorded at completion of the study. Visual inspection of the tibial inserts was used to identify regions of wear damage for SEM analysis (EVO MA15-Smart SEM, Zeiss, Germany)
Results
Extremely large material loss and wear was observed for both PEEK and CFR-PEEK inserts at 3Mc (Figure 1). The PEEK material showed higher volumetric loss than the CFR-PEEK. Wear rates of >200mm3/Mc compare with less than 4 mm3/Mc for polyethylene under the same conditions. [3]. Large, deep wear scars were observed on all plates (Figure 2a and b).
Evidence of mechanical material failure was observed through SEM including material cracking, deformation and fibre pull-out (Figure 3a and b).
Discussion
Wear simulator testing of flat PEEK and CFR-PEEK as potential replacements for polyethylene materials in a TKR configuration produced high material loss after 3Mc. This is in contrast to promising data reported in another study of the knee [5]. The present study examined a low-conformity condition. Previous studies have included hip and highly-conforming TKR designs; therefore the contact pressures would be lower than the current study. This study highlights these new materials may undergo mechanical failure at higher contact stress conditions.
