A practical model of osteomyelitis-induced bone pain by intra-tibial injection of Staphylococcus aureus in rats.

Osteomyelitis is an acute or chronic inflammatory process of bone accompanied with mild to severe pain. Generally, mild to moderate pain induced by osteomyelitis can be relieved, yet severe pain cannot. Therefore, a further investigation into the mechanism of severe pain induced by osteomyelitis is needed. In this study, a traditional rat model of osteomyelitis was induced by intra-tibial injection of Staphylococcus aureus. Then, a series of tests including bone histology, blood analysis, mechanical allodynia, thermal hyperalgesia, and immunohistochemistry were performed. Four days after an intra-tibial bacterial injection, acute inflammation was observed in the bone marrow, which developed into chronic inflammation 12 days after the procedure. The results from the blood analysis confirmed the existence of bone inflammation. Significant mechanical allodynia and thermal hyperalgesia developed shortly after the injection. This osteomyelitis-induced pain behavior was reversed by Celecoxib, a selective COX-2 inhibitor. Furthermore, significant increase of both microglia and astrocytes was observed in the spinal cord. Our results suggest that osteomyelitis-induced rats display pain related behaviors and associated neurochemical changes. This study thus provides a novel practical rat model of bone inflammation induced pain.