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.