BACKGROUND

Infrared thermal imaging is a non-invasive technique capable of detecting changes in temperature that could ultimately signify changes in blood supply. Flir One is a smartphone-based thermal camera, working by a downloadable application, capable of detecting the limb temperature through a non-contact method using infrared thermography technology. Using the Flir One camera, we will assess the lower limb reperfusion profile following the tourniquet release post total knee arthroplasty (TKA).

METHODS

A prospective study included 46 patients who underwent primary TKA. We used the (Flir One Gen 3) thermographic camera to capture images at ankle joint preoperatively, and at 1, 10, and 20 minutes post tourniquet release on operation side. The contralateral ankle stands as control.

RESULTS

The mean preoperative temperature (in Celsius) of ankle control side and operated side were 33.03 (SD=1.65) and 33.26 (SD=1.42), respectively. The mean ankle temperature on operation side was 19.73 (SD=2.85), 30.49 (SD=2), and 32.43 (SD=1.31) at 1, 10, and 20 minutes post tourniquet release, respectively, while the control side showed a mean temperature of 32.85 (SD=1.42), 32.84 (SD=0.91), and 33.15 (SD=0.95) at the same time intervals. There was a significant statistical difference between both ankle temperatures at 1 and 10 minutes (P=0.00 for each time). At 20 minutes, 37 ankles (80.4%) at operation side reached a temperature level similar but below the level of control side; however, the difference was not significant (P=0.692).

CONCLUSION

Infrared thermography using the smartphone-connected camera is a simple, non-invasive, feasible, and reliable technology. It provides an objective measure to assess the perfusion status of the limbs. In TKA, the distal limb will reach full reperfusion status after approximately 20 minutes of tourniquet release.