Abstract
Aim
Debridement, Antibiotics, Irrigation, and implant Retention (DAIR) is a surgical treatment protocol suitable for some patients with fracture related infection (FRI). Clinically relevant pre-clinical models of DAIR are scarce and none have been developed in large animals. Therefore, this project aimed to develop a large animal model for FRI including a DAIR approach and compare outcomes after 2 or 5 weeks of infection.
Method
Swiss Alpine sheep (n=8), (2–6 years, 50–80 kg) were included in this study. This study was approved by cantonal Ethical authorities in Chur, Switzerland. A 2 mm osteotomy was created in the tibia and fixed with a 10-hole 5.5 mm steel plate. Subsequently, 2.5 mL of saline solution containing 106 CFU/mL of Staphylococcus aureus MSSA (ATCC 25923) was added over the plate. Sheep were observed for 2 (n=3) or 5 weeks (n=5) until revision surgery, during which visibly infected or necrotic tissues were removed, and the wound flushed with saline. All samples were collected for bacterial quantification. After revision surgery, the sheep were treated systemically for 2 weeks with flucloxacillin and for 4 weeks with rifampicin and cotrimoxazole. After 2 further weeks off antibiotics, the animals were euthanized. Bacteriological culture was performed at the end of the study. Bone cores were isolated from the osteotomy site and processed for Giemsa & Eosin and Brown and Brenn staining. A radiographical examination was performed every second week.
Results
Bacteriological evaluation of the retrieved samples during revision surgery showed no significant difference between the 2 vs 5 weeks infection periods in term of total CFU counts. At the end of the study, radiographical examination showed callus formation over the osteotomy site in both groups, although the osteotomy was not completely healed in either group. At euthanasia, the 2 weeks infection group showed a higher soft tissue burden compared to the 5 weeks group, whereby the infection in the 5 weeks group was primarily located in the bone and bone marrow.
Conclusions
The large animal model of FRI and DAIR was successfully established. Bacteriological outcomes highlight that the increasing duration of the infection does not change the outcome but the location of the infection from a predominantly soft tissue infection to a deeper bone and intramedullary (IM) channel infection. The debridement of the IM channel could potentially reduce the infection burden by eliminating those bacteria not easily reached by systemic antibiotics, though is not practical using conventional techniques.
