An animal model for open femur fracture and osteomyelitis: Part I.

Infection is an everyday problem in orthopaedics and is quite common in open fracture management. To study this process and provide a basis to prevent infection, we developed a model that includes trauma (blunt fracture in the fashion of Bonnarens and Einhorn), surgical stabilization (standardized intramedullary K-wire fixation), and infection (Staphylococcus aureus inoculum). In this two-part study, we found that 10(2) colony-forming units of inoculum produced an optimal infection rate of 90-100%, which substantially challenged the immune system without overwhelming sepsis. We hypothesized that, in traumatic fractures, there is a specific immunological response that may lead to an increased rate of infection. In Part 2, we demonstrated immunosuppression (decreased Interleukin-12 levels) at days 6, 10, and 12 after fracture fixation versus nonfractured control groups (p < 0.05). This study describes a rat model of femur factures with osteomyelitis that allows investigation of posttraumatic immunosuppression.