Abstract
Bacterial resistance in joint replacement surgery is an emerging problem. A review of the bacteriology from infected revisions performed at Wrightington over the past 5 years has shown that the most common organism is coagulase negative staphylococcus (59%), followed by staphylococcus aureus (17%).
The sensitivity profiles are shown below.
| Antibiotic | Sensitive | Resistant |
|---|---|---|
| Methicillin | 62 | 38 |
| Fucidic acid | 90.7 | 9.3 |
| Gentamicin | 68 | 32 |
| Erythromycin | 69 | 31 |
| Clindamycin | 90.7 | 9.3 |
| Vancomycin | 99.25 | 0.75 |
| Teicoplanin | 96.4 | 3.6 |
Gentamicin is the most commonly pre formulated antibiotic added to acrylic bone cement. The above data clearly demonstrates that for 32% of infected cases gentamicin alone is inadequate prophylaxis. As a consequence of this the use of additional antibiotics for resistant cases is becoming commonplace.
The aim of this study was to investigate the mechanical properties of additional antibiotics in acrylic bone cement.
The 7 antibiotics listed above were selected on the basis of sensitivity to organisms isolated at revision for deep infection. Each was added at a loading of 1g active to CMW1 RO (plain) and CMW1 G (gentamicin). The antibiotics were mixed with the polymer by hand. The cement was then mixed as per manufacturer’s instructions.
Dough and setting times were noted. Standard samples were produced using ISO approved moulds. Each antibiotic/cement combination was tested for compression strength, impact strength and flexural strength.
All antibiotic/cement combinations performed as well as the control mix when tested for compression and impact strength. The flexural strength results for fusidic acid and erythromycin when added to acrylic cement were comparable to the control mix. Flucloxacillin, clindamycin and teicoplanin did lower the flexural strength to just below acceptable limits. However Vancomycin when added at 1g active reduced the flexural strength of acrylic bone cement significantly.
Although vancomycin may remain one of the last bastions of antibiotic therapy our study suggests that’s its addition to acrylic bone cement significantly weakens its mechanical properties. We would advise caution in its use as this may reduce the chances of long term success when undertaking revision for deep infection.
The abstracts were prepared by Peter Kay. Correspondence should be addressed to him at Centre for Hip Surgery, Wrightington Hospital, Appley Bridge, Wigan WN6 9EP.
