[Animal models of osteomyelitis]

Establishment of a reliable in-vivo model of implant-associated infection to investigate innovative treatment options

The increasing number of implant-associated infections and of multiresistant pathogens is a major problem in the daily routine. In the field of osteomyelitis, it is difficult to manage a valid clinical study because of multiple influencing factors. Therefore, models of osteomyelitis with a simulation of the pathophysiology to evaluate treatment options for implant-associated infections are necessary. The aim of this study is to develop a standardized and reproducible osteomyelitis model in-vivo to improve treatment options. This study analyses the influence of a post-infectious implant exchange one week after infection and the infection progress afterward in combination with a systemic versus a local antibiotic treatment in-vivo. Therefore, the implant exchange, the exchange to a local drug-delivery system with gentamicin, and the implant removal are examined. Furthermore, the influence of an additional systemic antibiotic therapy is evaluated. An in-vivo model concerning the implant exchange is established that analyzes clinic, radiologic, microbiologic, histologic, and immunohistochemical diagnostics to obtain detailed evaluation and clinical reproducibility. Our study shows a clear advantage of the combined local and systemic antibiotic treatment in contrast to the implant removal and to a non-combined antibiotic therapy. Group genta/syst. showed the lowest infection rate with a percentage of 62.5% concerning microbiologic analysis, which is in accordance with the immunohistochemical, cytochemical, histologic, and radiologic analysis. Our in-vivo rat model has shown valid and reproducible results, which will lead to further investigations regarding treatment options and influencing factors concerning the therapy of osteomyelitis and implant-associated infections.

A new animal model for delayed osseous union secondary to osteitis

Background

The treatment of infection-related delayed bone unions is still very challenging for the orthopedic surgeon. The prevalence of such infection-related types of osteitis is high in complex fractures, particularly in open fractures with extensive soft-tissue damage. The aim of this study was to develop a new animal model for delayed union due to osteitis.

Methods

After randomization to infected or non-infected groups 20 Sprague–Dawley rats underwent a transverse fracture of the midshaft tibia. After intramedullary inoculation with staphylococcus aureus (10³ CFU) fracture stabilization was done by intramedullary titanium K-wires. After 5 weeks all rats were euthanized and underwent biomechanical testing to evaluate bone consolidation or delayed union, respectively. Micro-CT scans were additionally used to quantitatively evaluate the callus formation by the score of Lane and Sandhu. Blood samples were taken to analyze infectious disease markers (day 1, 14 and 35).

Results

Biomechanical testing showed a significant higher maximum torque in the non-infected group 5 weeks postoperatively compared with the infected group (p < 0.001). According to the Lane and Sandhu score a significantly higher callus formation was found in the non-infected group (p < 0.001). Similarly, the leucocyte count in the infected group was significantly higher than in the non-infected group (p < 0.05).

Conclusions

Here we have established a new animal model for delayed osseous union secondary to osteitis. The animal model appears to be appropriate for future experimental studies to test new therapeutic strategies in these difficult to treat bone healing complications.

A model of implant-associated infection in the tibial metaphysis of rats

OBJECTIVE

Implant-associated infections remain serious complications in orthopaedic and trauma surgery. A main scientific focus has thus been drawn to the development of anti-infective implant coatings. Animal models of implant-associated infections are considered helpful in the in vivo testing of new anti-infective implant coatings. The aim of the present study was to evaluate a novel animal model for generation of implant-associated infections in the tibial metaphysis of rats.

MATERIALS AND METHODS

A custom-made conical implant made of Ti6Al4V was inserted bilaterally at the medial proximal tibia of 26 female Sprague-Dawley rats. Staphylococcus aureus in amounts spanning four orders of magnitude and each suspended in 15  μ l phosphate buffered saline (PBS) was inoculated into the inner cavity of the implant after the implantation into the defined position. Controls were treated accordingly with PBS alone. Animals were then followed for six weeks until sacrifice. Implant-associated infection was evaluated by microbiological investigation using swabs and determination of viable bacteria in the bone around the implant and the biofilm on the implants after sonification.

RESULTS

Irrespective of the initial inoculum, all animals in the various groups harbored viable bacteria in the intraoperative swabs as well as the sonication fluid of the implant and the bone samples. No correlation could be established between initially inoculated CFU and population sizes on implant surfaces at sacrifice. However, a significantly higher viable count was observed from peri-implant bone samples for animals inoculated with 10(6) CFU. Macroscopic signs of animal infection (pus and abscess formation) were only observed for implants inoculated with at least 10(5) CFU S. aureus.

DISCUSSION/CONCLUSION

The results demonstrate the feasibility of this novel animal model to induce an implant-associated infection in the metaphysis of rats, even with comparatively low bacterial inocula. The specific design of the implant allows an application of bacteria in reproducible numbers at well-defined contact sites to the animal bone.

[Multistep surgery for spondylosyndesis. Treatment concept of destructive spondylodiscitis in patients with reduced general condition]

OBJECTIVE

Retrospective assessment of multistage surgery in the treatment of progressive spondylodiscitis in patients with critical physical status.

PATIENTS

A total of 34 patients (mean age 58.6 years) with 37 progressive spondylodiscitis foci and destruction of one to three vertebral segments (1.9 mean) were recorded within an 8-year period. Time between first complaints and operative treatment was 3 months (mean). Preoperative health status was critically reduced in 11 patients (ASA IV) and poor general condition (ASA III) was seen in 23 patients when vital indication was seen preoperatively. Considerable systemic disease (n=31), further infection focus (n=18), and nosocomial trauma (n=5) were causally related. Spondylodiscitis was seen more frequently in the lumbar (n=20) and thoracolumbar than in the thoracic (n=10) and cervical spine (n=1). Staphylococcus aureus was detectable from operative specimens and hemoculture in 15 cases, MRSA in 6 of these.

METHODS

In cases of monosegmentary involvement (n=7) ventral debridement, biopsy, and application of antibiotic chains were followed by autologous interbody bone grafting in a second stage operation. In 29 cases with destruction of two (n=27) and three (n=3) segments, posterior instrumentation including laminectomy in 4 patients was completed by anterior debridement and application of antibiotic chains during a first surgical intervention. After stabilization of physical condition and having reached a macroscopically indisputable implant bed, the ventral fusion with autologous interbody bone grafting or cage in combination with a plate or internal fixation system was performed as the last of several surgical steps.

RESULTS

No case of perioperative mortality was observed. Intensive care continued 9.1 days and hospitalization 49.5 days (mean). During a 37.6-month follow-up two late recurrences were observed.

CONCLUSION

A multistep surgical procedure under protection of dorsal instrumentation can limit perioperative mortality in patients in critical general condition by avoiding an extended one stage dorsoventral spondylodesis. After eradication of further infection foci and stabilization of physical condition, ventral instrumentation is completed under elective conditions.