Histological score for degrees of severity in an implant-associated infection model in mice.

INTRODUCTION: Several scores were introduced to diagnose and to classify osteomyelitis in practice. Mouse models are often used to study the pathophysiology of bone infection and to test therapeutic strategies. Aim of the present study was to design a score to diagnose and quantify implant-associated infection in a murine experimental model. MATERIALS AND METHODS: Four independent parameters were developed: existence of callus, consolidation of the fracture, structural changes of the medullary cavity and number of bacteria. The score was assessed in a standardized implant-associated mouse model with 35 BALB/c-mice. The left femur was osteotomized, fixed by a titanium locking plate and infection was induced by inoculation of Staphylococcus aureus into the fracture gap. For the sham group, the procedure was performed without inoculation of bacteria. The score was assessed on days 7, 14 and 28. Each item of the score showed lower values for the infection group compared to the controls after 4 weeks. RESULTS: Regardless of the assessed time point, the overall total score was significantly higher in the control group compared to the infection group (p < 0.0001). Analysis revealed a sensitivity of 0.85, specificity of 1.0, negative predictive value of 0.67 and positive predictive value of 1.0. CONCLUSION: The proposed score assessing severity of fracture-related infection in an implant-associated murine model was easy to access, feasible to diagnose and estimate bone healing and infection in a murine bone infection with a high sensitivity. Therefore, this score might be a useful tool to quantify infection-related changes after fracture in further future preclinical studies.

Effect of hyperbaric oxygen therapy (HBO) on implant-associated osteitis in a femur fracture model in mice.

Hyperbaric oxygen therapy (HBO) is applied very successfully in treatment of various diseases such as chronic wounds. It has been already suggested as adjunctive treatment option for osteitis by immune- and fracture modulating effects. This study evaluates the importance of HBO in an early implant-associated localized osteitis caused by Staphylococcus aureus (SA) compared to the standard therapy. In a standardized murine model the left femur of 120 BALB/c mice were osteotomized and fixed by a titanium locking plate. Osteitis has been induced with a defined amount of SA into the fracture gap. Debridément and lavages were progressed on day 7, 14, 28 and 56 to determine the local bacterial growth and the immune reaction. Hyperbaric oxygen (2 ATA, 90%) was applied for 90 minutes on day 7 to 21 for those mice allocated to HBO therapy. To evaluate the effect of HBO therapy the following groups were analyzed: Two sham-groups (12 mice / group) with and without HBO therapy, two osteotomy groups (24 mice / group) with plate osteosynthesis of the femur with and without HBO therapy, and two osteotomy SA infection groups (24 mice / group) with and without HBO therapy. Fracture healing was also quantified on day 7, 14, 28 and 56 by a.p. x-ray and bone healing markers from blood samples. Progression of infection was assessed by estimation of colony-forming units (CFU) and immune response was analyzed by determination of polymorphonuclear neutrophils (PMN), Interleukin (IL) - 6, and the circulating free DNA (cfDNA) in lavage samples. Osteitis induced significantly higher IL-6, cfDNA- and PMN-levels in the lavage samples (on day 7 and 14, each p < 0.05). HBO-therapy did not have a significant influence on the CFU and immune response compared to the standard therapy (each p > 0.05). At the same time HBO-therapy was associated with a delayed bone healing assessed by x-ray radiography and a higher rate of non-union until day 28. In conclusion, osteitis led to significantly higher bacterial count and infection parameters. HBO-therapy neither had a beneficial influence on local infection nor on immune response or fracture healing compared to the standard therapy in an osteitis mouse model.