Abstract
ABSTRACT
The friction and lubrication behaviour of four Biomet ReCap components with a nominal diameter of 52 mm and diametral clearance ranging from 167-178 μm were investigated using a friction hip simulator. Friction testing was carried out using pure bovine serum and aqueous solutions of bovine serum (BS), with and without carboxymethyl cellulose (CMC), adjusted to a range of viscosities (0.001-0.236 Pas). The Stribeck analyses suggested mixed lubrication as the dominant mode with the lowest friction factor of 0.07 at a viscosity of 0.04 Pas.
INTRODUCTION
The femoral resurfacing systems provide an alternative to hemi and total hip arthroplasty and offer several unique advantages including large resurfacing heads (>35–60 mm diameter) allowing increased range of motion (and stability) over the traditional 28 mm artificial hip joints, with excellent tolerances and surface finish leading to a reduction in wear, as well as preserving primary bone with the femoral canal remaining untouched. This work has investigated the friction and lubrication behaviour of four 52 mm metal-on-metal Biomet ReCap components with a clearance of 167-178 μm using serum-based lubricants.
MATERIALS AND METHODS
Four as-cast, high carbon, cobalt-chrome resurfacing systems (supplied by Biomet UK Healthcare Ltd, Swindon) with a nominal diameter of 52 mm each and diametral clearance of 167-178 μm were used in this study. Frictional measurements of all the joints were carried out at University of Bradford, Medical Engineering Department, using a Prosim Hip Joint Friction Simulator (Simulation Solutions Ltd, Stockport, UK). For the friction factors, an average of three independent tests was taken and each test was run using; 100% bovine serum (BS) and then aqueous solutions of 25% v/v BS in distilled water with varying quantities of CMC to obtain viscosities of; 0.0015 Pas (pure BS), 0.0013 Pas (25% BS), 0.00612 Pas (25% BS, 1 g CMC), 0.01274 Pas (25% BS, 2 g CMC) and 0.236 Pas (25% BS, 5 g CMC) at a shear rate of 3000 s-1. All viscosities were measured using a RHEOPLUS/32 V3.40.
RESULTS AND DISCUSSION
The Stribeck curves for all four ReCap components showed a very similar trend, i.e. the friction factors decreased from ∼0.11 to ∼0.07 as the Sommerfeld number increased (i.e. as viscosity increased from 0.0015 to 0.0127 Pas) indicating a mixed lubrication regime up to a viscosity of 0.0127 Pas; above which the friction factor increased to ∼ 0.13 at a viscosity of 0.236 Pas. These results clearly suggest that the Biomet ReCap components showed low friction (at the physiological viscosities ∼0.01 Pas) with mixed lubrication as the dominant mode.
