Abstract
The visco-elastic behaviour of acrylic bone cement is a key feature of cement-implant performance. The ability of the cement to creep in conjunction with a force-closed design of stem (collarless polished taper) affords protection of the vital bone-cement interface. Most surgeons in the UK use antibiotic-laden PMMA in primary total joint arthroplasty. In revision surgery the use of bespoke antibiotic-cement combinations is common.
The aim of this study was to elicit the effect of antibiotics upon the physical properties of bone cement.
Methods: The static properties of the cements were assessed following protocols described in ISO 5833: 2002, while the viscoelastic properties of the cement were measured with in-house developed apparatus in quasi-static conditions. Creep tests were performed in four point bending configuration over a 72 hour period in physiological conditions. Porosity was measured on the mid cross section of the creep samples using a digital image technique.
The cements used were Palacos R40 and Palacos R with gentamicin. The antibiotics added included fucidin, erythromycin, teicoplanin and vancomycin in 500mg powder aliquots up to a maximum of 1g per 40 g mix.
All data were analysed using ANOVA with Bonfer-roni post-hoc test. Pearson’s correlation coefficient was used to investigate the association between physical factors (SPSS).
Results: The static and working properties did not vary significantly with antibiotic additions. The mean creep of the cement increased in line with the amount of antibiotic added. The specific antibiotic was not relevant. The differences were statistically significant. Mean porosity also increased with antibiotic mass. There was a linear relationship between cement porosity and creep!
Conclusions: Despite modern mixing techniques the porosity of bone cement increases with antibiotic additions. This increased porosity is related to the greater creep seen in the cement. Surgeons should apply these findings when planning revision hip surgery.
Correspondence should be addressed to Mr Carlos Wigderowitz, Senior Lecturer, University Department of Orthopaedic and Trauma Surgery, Ninewells Hospital and Medical School, Dundee DD1 9SY.
