Abstract
Injections of hyaluronic acid solutions, often known as visco-supplements, into the joints of patients suffering from osteoarthritis are an accepted therapy. In most replacement joints, wear of the biomaterials used in them is a critical concern. For in vitro wear tests of such materials the recommended lubricant is one based on bovine serum. However, unlike synovial fluid, bovine serum does not contain hyaluronic acid. The aim of the work reported here was to take a clinically used hyaluronic acid solution, Ostenil, and to investigate its influence on the wear of two orthopaedic biopolymers
Ultra high molecular weight polyethylene (UHMWPE) and poly tetra fluoro ethylene (PTFE) were tested in turn using a four-station, multi-directional, pin-on-plate wear test rig which had previously been shown to reproduce clinical wear factors for UHMWPE, PTFE and polyacetal. For each biopolymer three lubricants were employed: 33% bovine serum (2 stations); 33% bovine serum + Ostenil (1 station); and distilled water + Ostenil (1 station). Polymeric test pins were subject to a load of 40N and articulated against polished stainless steel plates. Wear factors were determined by dividing the volume lost by the product of the load and the sliding distance (units × 10-6mm3/Nm).
The UHMWPE wear tests ran to 66.3km sliding distance. The addition of Ostenil to dilute bovine serum resulted in a wear factor of 1.4 × 10-6mm3/Nm for UHMWPE. The wear factor was 1.6 × 10-6mm3/Nm when dilute bovine serum alone was used as the lubricant. This shows good agreement with a wear factor of 2.1 × 10-6mm3/Nm reported for failed UHMWPE acetabular cups. PTFE provides an accelerated wear test with clinical validity. In the presence of 33% bovine serum a mean wear factor for PTFE of 40 × 10-6mm3/Nm was measured. The wear factor was 59 × 10-6mm3/Nm for dilute bovine serum plus Ostenil. For explanted PTFE acetabular cups a wear factor of 37 × 10-6mm3/Nm has been calculated. For both polymers wear was least when the lubricant was distilled water plus Ostenil. However a transfer film was found and such films are not clinically valid.
Correspondence should be addressed to Dr Roger Bayston, Division of Orthopaedic and Accident Surgery, Queen’s Medical Centre, Nottingham, NG7 2UH, England.
