IR Thermography May Help Diagnose Joint Inflammation

Noninvasive, low-cost IR thermography may be effective for imaging joint inflammation and also shows promise for assessing ergonomic problems caused by office work.

A study at the University of Eastern Finland evaluated the capability of IR thermography to detect inflammation in the knee and ankle joints of 58 children suffering from conditions such as juvenile idiopathic arthritis or autoimmune disease with arthritis, such as systemic lupus erythematosus.

Human skin emits IR radiation almost like a perfect blackbody — that is, one that absorbs all incoming light and reflects none. IR thermography is thus well suited for the measurement of skin temperature. Although the human core temperature may be indicative of several bodily dysfunctions, there is a lack of scientific evidence about which musculoskeletal diseases or conditions can be diagnosed by evaluating skin surface temperature.

An example case of ankle joint inflammation showing that the maximum skin temperature around the inflamed joint is higher than in the noninflamed joint. Courtesy of Roope Lasanen.

The researchers found that skin surface temperatures were significantly elevated in inflamed ankle joints, but not in inflamed knee joints. No significant difference was found between the skin surface temperatures of two aspects of ankle joints: the medial, or central area, and the lateral, or side area. In knee joints, the mean temperatures of medial and lateral aspects differed significantly.

The researchers concluded that thermal imaging may have potential for detecting joint inflammation in ankle joints of children, while for knee joints, the results were inconclusive and warrant further research.

The study also analyzed skin temperature in relation to various musculoskeletal conditions. Work ergonomics was evaluated by means of IR thermography and surface electromyography, combined with a subjective assessment conducted by a neck disability index. The study found that IR thermography demonstrated potential for evaluating office ergonomics and that spatial variation of upper-back skin temperature was a promising measure in ergonomic assessments.

Another aspect of the study used IR thermography to evaluate the effect on skin temperature of the menthol concentration in cold gels commonly used for the treatment of muscle injuries. While such products are widely used, little is known about how the menthol concentration affects skin temperature. The study found that changes in the menthol concentration did not seem to have any significant effect on skin cooling. Furthermore, cold gels did not have a significant effect on skin temperature in skin areas adjacent to the gel application site.

The study was published in Physiological Measurement (doi: http://dx.doi.org/10.1088/0967-3334/36/2/273).