INTRODUCTION: Articulating metallic implants have a detrimental influence on medical imaging. Polyetheretherketone (PEEK) is already used as a structural implant material in the spine, has the stiffness to provide a stable implant-bone interface and is suitably radiolucent. The purpose of the present study is to further examine the pin-on-plate wear of various PEEK-PEEK pairings and the effects of varied lubricant properties, reinforcement orientation, and pin contact radii. METHODS: Wear testing of self mating unfilled PEEK Optima (OPT) and carbon fiber reinforced (CFR) PEEK provided by Invibio Ltd. was performed using a six station OrthoPOD™ pin on disc apparatus (AMTI). A crossing path motion was achieved with a pin rotation of 87° and oscillation of the plate resulting in a stroke length of 17 mm applied at a frequency of 1 Hz. Two lubricant protein concentrations were used; 12 g/L, and 6 g/L. RESULTS: From 0.25–1.0 Mc OPT exhibited a steady state wear rate of 0.094 mm3Mc-1, compared to 0.170 mm3Mc-1 for CFR. When the protein concentration of the lubricant was reduced from 12 to 6 gL-1, the wear rate of OPT increased significantly while the wear rate of CFR increased slightly to 0.254 mm3Mc-1. DISCUSSION: The present study seems to show a weak correlation between protein concentration and wear for the CFR specimens. Parallel fiber orientation at the contact area and/or reduced contact radius appeared to increase to run-in wear in CFR. The effects of protein concentration is important as different implant applications will observe varying lubrication properties with a lower protein concentration expected in the spinal disc space compared to a synovial joint.

A knee testing rig is a biomechanical testing device specifically designed for investigating the kinematics and kinetics of cadaveric human knee-joint specimens during knee-flex stance simulations. Current in-vivo measurements of patients can provide assessments of displacement and rotation but do not permit quantification of internal forces and movement of internal structures. More importantly, the detailed study of the effects of surgical reconstruction methodologies, implant designs and knee pathologies on lower extremity mechanical is only possible using knee testing rigs in the laboratory. We proposed the design of a knee rig with aims to measure these parameters under a full body weight knee simulation. The knee rig may potentially be used to investigate the effect of ligament injury, post-surgical ligament reconstruction, and evaluating implant designs in terms of its resulting knee kinematics and load distribution. A CAD model of the rig was designed and evaluated using SolidWorks and then machined. The constructed rig consists of ‘hip’ and ‘ankle’ assemblies, which combine to allow a natural six degrees of freedom of movement. These include three rotations: flexion/extension, abduction/adduction, internal/external tibia rotation and three translations: anterior/posterior, medial/lateral, proximal/distal. Knee simulation is performed by pulling the quadriceps tendon of a cadaveric knee specimen to produce a realistic muscle action. A 6-axis load cell (AMTI MC3A–6-1000) is used to collect force/moment data. A motion capture system is used to measure the resulting knee kinematics during flexion.