Thermal Imaging as a Noninvasive Diagnostic Tool for Anterior Knee Pain Following Implantation of Artificial Knee Joints

The variety of radiographic diagnostics used to diagnose pain localised close to metal implants is still limited. Especially magnetic resonance results can not be analysed because of artefacts. In this article we present for the first time a direct correlation between an increase in skin temperature and existent frontal (anterior) knee pain after implantation of artificial knee joints measured with thermography. In a standardised way 26 knees were analysed. Thermographic photos were taken from frontal, inner (medial) and outer (lateral) directions with a computer-assisted infrared thermograph. Temperatures in locations with pain were significantly higher compared to the reference field in inner location (median 0.95 degrees C, p=0.0043), as well as in outer location (median 0.5 degrees C, p=0.032). Median temperature difference between pain localization and localizations without pain was 0.7 degrees C and ranged from 0.1 degrees C to 1.7 degrees C. In the receiver operating characteristic (ROC) analysis the sensitivity of this method was 1.0 and specificity was 0.917. The evidence of a significant increase in skin temperature on the painful sites opens up the possibility to localize and assess pain more precisely in patients with joint prosthesis. We consider this novel, rapid, inexpensive and non-invasive technology to posses the potential to become a useful and objective tool for diagnosis of pain and inflammation and to generate digital data that can be stored and analysed in clinical practice.