Abstract
Introduction and Aims: Official governmental data indicates that infection rates for hip and knee replacement vary between zero and eight percent between institutions with and average rate of between one and two percent. Despite an apparent increase in our understanding of infection and increased use of antibiotics, decontamination and surgical technology infection remains a major problem, accounting for up to 10% of all revision procedures. The aim of this paper is to review where infection comes from, what turns a contamination into an infection and how infection can be avoided.
Method: The organisms causing contamination of 125 primary joint replacements have been studied prospectively and compared to the organisms found at 334 revisions for deep infection. The antibiotic sensitivities, virulence and genetic ability to produce biofilms have been studied. The use of pre-operative screening for MRSA in 9000 patients undergoing elective surgery is compared to 2500 microbiological specimens taken for possible infection during the same time period to assess the importance of MRSA in prosthetic infection. The genetic susceptibility to infection, relationship between post-operative pyrexia and deep prosthetic infection and the use of blood transfusion and infection is investigated.
Results: At least 70% of all primary joint replacements are contaminated with bacteria. The commonest contaminant is Staph. epidermidis, which is the commonest organism causing deep infection. The Staph. epidermidis causing deep infection is genetically a much stronger producer of biofilms than other strains of Staph. epidermidis. Five percent of the contaminating Staph. epidermidis is multi-resistant to antibiotics and is not susceptible to routine antibiotic prophylaxis. In our institution all elective patients are screened for MRSA. One percent of patients are carriers. Deep infection with MRSA is uncommon, with MRSA accounting for less than 2% of cases, however infection with Staph. epidermidis is the most common accounting for 60% of all infection, but of concern is that 55% of all infecting Staph. epidermidis is methicillin-resistant. The organism of concern is therefore MRSE not MRSA. Post-operative pyrexia actually protects against infection. The temperature charts of 40 patients who subsequently developed deep infection when compared to the charts of 200 patients without deep infection indicates that a low post-operative temperature is associated with an increased risk of infection, possibly indicating depressed immunity. Post-operative blood transfusion in 100 patients is shown to decrease immunity and increase nosocomial infection and wound healing problems, indicating that the immune modulation at the time of surgery is probably a major factor in post-operative infection. Finally, comprehensive genetic studies in patients undergoing long-term follow-up at Wrightington indicate definite genetic susceptibility to deep infection in certain patient groups.
Conclusion: We do not understand prosthetic infection. We screen and worry about the wrong organisms, we wrongly worry about post-operative pyrexia, we increase the susceptibility of our patients to infection by blood transfusion and give the wrong antibiotics. We may be able to completely avoid infection if we redirect our efforts and stop relying on powerful broad spectrum antibiotics alone.
These abstracts were prepared by Editorial Secretary, George Sikorski. Correspondence should be addressed to Australian Orthopaedic Association, Ground Floor, The William Bland Centre, 229 Macquarie Street, Sydney, NSW 2000, Australia.
At least one of the authors is receiving or has received material benefits or support from a commercial source.
