Local temperature elevation as a marker of spinal implant infection in an animal model

BACKGROUND: Temperature elevation, a classic marker of infection and local temperature elevation, might be a useful predictor of early infection. However temperature measurement around the spine is not readily accessible. The purpose of this study was to explore whether a temperature sensing implant might reproducibly detect local temperature change associated with peri-implant wound infection, in a rabbit model. METHODS: Twelve adult rabbits were implanted with a spinal screw-rod construct. Temperature probes were placed at the implantation site as well as at a separate scapular site away from the surgical site to serve as control. Animals were inoculated with S. aureus: group 1 (saline control), group 2 (low dose 1 × 10(2) CFU/site), group 3 (medium dose 1 × 10(4) CFU/site), and group 4 (high dose 1 × 10(6) CFU/site) and monitored for 7 days prior to euthanasia. RESULTS: The scapular control temperature and implant site temperature in the non-infected animals remained similar throughout the study period. Both the scapular control and implant site temperatures were elevated in the infected animals compared to the non-infected animals. There was a statistically significant difference in the scapular control temperature and implant site temperature in all infected animals but not in the non-infected animals. Difference in temperature elevation between implant site and control scapular site were greatest for the animals with worst clinical appearance during the post-mortem evaluation. CONCLUSIONS: This rabbit model demonstrates that local temperature measured in proximity to a spinal implant is elevated in the presence of infection with greater elevations associated with worse infections. Availability of an implantable temperature sensor may yield valuable information for the assessment and treatment of suspected spinal wound infection in the clinical setting.