The Value of Thermal Imaging for Knee Arthritis: A Single-Center Observational Study

To compare (non-contact) thermal imaging with power Doppler (PD) for the evaluation of knee arthritis with joint effusion.

We enrolled patients with knee arthritis who were scheduled to undergo an arthrocentesis of the knee from April to December 2020 at a single tertiary hospital. A thermography camera, FLIR ONE Pro, was used to obtain both thermographic and digital images on subjects. For each subject, thermography, ultrasonography, arthrocentesis, and blood tests were conducted at the same study visit. Thermal imaging findings and clinical characteristics were compared by dividing the subjects into PD-positive and PD-negative groups on ultrasound. The receiver operating characteristic (ROC) curve analysis was used to determine the accuracy of PD positivity.

A total of 30 knee arthritis patients were enrolled in this study. Knee temperature was significantly higher in PD-positive group compared to PD-negative group [maximum temperature (T max): 33.2℃ vs. 30.5℃, p=0.025; minimum temperature (T min): 30.7℃ vs. 27.0℃, p=0.015; average temperature (T ave): 32.1℃ vs. 29.1℃, p=0.016]. Also, the joint fluid white blood cell count was considerably higher in PD-positive group than in PD-negative group (24556 cells/mm³ vs. 7840 cells/mm³, p=0.010). The area under the ROC curve of the point measurement of T max, T min, and T ave ranged between 0.764 and 0.790.

In this study, we found that high thermographic temperatures of the knee suggest a positive PD signal. Thus, thermography might be used as an adjuvant tool of PD for non-invasive evaluation of knee arthritis.