Degenerative Joint Damage Is Not a Risk Factor for Streptococcal Sepsis and Septic Arthritis in Mice

Septic arthritis (SA) is an aggressive joint disorder causing invalidity and mortality. Although epidemiological studies suggest osteoarthritis (OA) as a risk factor for SA, experimental insights into the relatedness of both diseases are lacking. We therefore sought to investigate whether pre-existing OA indeed promotes SA frequency or severity. We used STR/ort mice that spontaneously develop OA and, in addition, induced OA via anterior cruciate ligament transection (ACLT) in C57BL/6J mice. Mice were infected with Group A Streptococcus (GAS) and then were monitored for clinical signs of sepsis and SA. Sepsis was confirmed via elevated inflammatory cytokines in plasma, while bone morphology was assessed by micro-computed tomography. Cartilage integrity was evaluated histologically. Mice with spontaneous OA developed life-threatening SA, with GAS only moderately affecting the femoral bone structure. Surgically induced OA neither impacted on SA incidence nor on mortality when compared to infected mice without the preceding joint disease. Furthermore, only insignificant differences in bone morphology were detected between both groups. Our data indicate that degenerative joint damage due to ACLT, by itself, does not predispose mice to SA. Hence, we propose that other factors such as prosthetic joint replacement or high age, which frequently coincide with OA, pose a risk for SA development.