Can pin-site inflammation be detected with thermographic imaging? A cross-sectional study from the USA and Denmark of patients treated with external fixators.

Background and purpose:  Patients with external fixators are at risk of pin-site infection. A tool for objective monitoring of pin sites for evolving signs of infection is warranted. We aimed to investigate the temperature (MaxTp) difference between clean and visually inflamed pin sites using thermography and to establish the optimal cut-off value of MaxTp using thermography as a screening tool for inflammation detection.

Methods:  This was a cross-sectional study performed in the USA and Denmark of patients with circular external fixators. Pin sites were visually judged by a surgeon or a nurse as clean or as showing signs of inflammation. The MaxTp was obtained at the pin site by thermographic imaging using an infrared camera (FLIR T540).

Results:  We included 1,970 pin sites from 83 patients. The mean MaxTp for clean pin sites (n = 1,739) was 33.1°C (95% confidence interval [CI] 32.8-33.4) and the mean MaxTp for visual inflamed pin sites (n = 231) was 34.0°C (CI 33.6-34.3). The mean difference, when adjusted for repeated observations of patients and pin sites, was statistically significant with a difference of 0.9°C (CI 0.7-1.1) (P < 0.001). The area under the receiver operating characteristic curve for MaxTp as a screening tool to detect visual signs of inflammation was 0.71 (CI 0.65-0.76). The empirically optimal cut-off value was 34.1°C with a sensitivity of 65%, a specificity of 72%, a positive predictive value of 23%, and a negative predictive value of 94%.

Conclusion:  We found a statistically significant difference in mean temperature between pin sites with and without visual signs of inflammation. Thermography could be a promising tool for future point of care technology for monitoring inflammation around pin sites.