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Local plate infections in a rabbit model
A Johansson1, J U Lindgren, C E Nord
1Department of Surgery, Anaesthesiology, Radiology, and Orthopedics, Karolinska Institutet, Huddinge University Hospital, Sweden.
Abstract:
We used 30 New Zealand white rabbits to compare the susceptibility to bacterial challenge of two different orthopaedic implants: a standard-design stainless steel plate, or a PC-FIX titanium plate applied on the right tibia were compared with sham operated animals. Directly after surgery Staphylococcus aureus (10(8)-10(9) colony forming units) were inoculated close to the plate. The infection rate in the group of plated animals was 11/20 (stainless steel plates 6/10, PC-FIX titanium plates 5/10) and in sham operated animals only 1/10. Thus, a foreign body increased the risk for infection (p = 0.02). However, the implant type did not appear to be of major importance when the bacteria were inoculated locally. In experimental haematogenous infections, by contrast, implant design and material are considered to be important. This may either indicate different pathogenic mechanisms in locally and haematogenously induced infections, or simply that the large number of microorganisms in local inoculation 'overload' the normal defence systems.
Insights
Orthopaedic implants increase infection risk, but the material (stainless steel vs. titanium) did not significantly alter outcomes in this rabbit model with local Staphylococcus aureus inoculation. Implant type may matter more in bloodstream infections.
Area of Science:
- Orthopaedic Surgery
- Infectious Disease
- Biomaterials Science
Background:
- Surgical site infections are a significant complication of orthopaedic implants.
- The role of implant material and design in infection susceptibility requires further elucidation.
- Bacterial inoculation method may influence infection development and implant material relevance.
Purpose of the Study:
- To compare the susceptibility to bacterial challenge of stainless steel and titanium orthopaedic implants.
- To evaluate the impact of local bacterial inoculation on implant-associated infection rates.
- To investigate potential differences in infection mechanisms between local and haematogenous bacterial spread.
Main Methods:
- Thirty New Zealand white rabbits underwent tibial surgery with either a stainless steel plate, a PC-FIX titanium plate, or a sham procedure.
- Staphylococcus aureus (10^8-10^9 CFU) was inoculated locally near the implant immediately after surgery.
- Infection rates were compared between implant groups and the sham-operated control group.
Main Results:
- The overall infection rate in animals with implants was 11/20, compared to 1/10 in sham-operated animals (p = 0.02).
- No significant difference in infection rates was observed between stainless steel (6/10) and PC-FIX titanium (5/10) plates.
- Local inoculation of a high bacterial load appeared to 'overload' host defense mechanisms, potentially masking implant material effects.
Conclusions:
- The presence of an orthopaedic implant significantly increases the risk of local bacterial infection.
- Implant material (stainless steel vs. titanium) did not influence infection rates in this model of local Staphylococcus aureus inoculation.
- Differences in pathogenic mechanisms or bacterial load may explain why implant material is considered important in haematogenous infections but not local ones.