While island flaps such as the V-Y advancement island flap, the Bezier flap and the Keystone Design Island flap are often mentioned in the context of perforator-based island flaps of the lower limb, one issue with conventional island flaps is that when tissue is advanced or transposed, a twist of the tissue occurs and this increases the external pressure on the venous supply. It is a well-known plastic surgical dictum that fascio-cutaneous flaps, once ‘islanded,’ are solely reliant on the venae comitantes for venous drainage. Therefore, it is important to know where reliable venous perforator drainage exists as this can help plan the location of such islands. We therefore set out to study lower limbs using a thermal imaging camera to see we could find reliable perforator locations in the lower limbs that could help design perforator-based fascio-cutaneous flaps.
Innovation
For this study we used a thermal imaging camera (FLIROne for iPhone, manufactured by Flir Systems Inc., Wilsonville, OR, USA) to take images of lower limbs prior to cutaneous surgery. This device contains a non-contact spot temperature measurement with automatic shuttering, and has been designed to capture a thermal reading of photographic images—and therefore in the past, has been primarily used in detecting leaks in buildings.
The technique for using the FLIROne Camera to venous perforators has already been defined. Suphachokauychai et al. [
4] have already provided guidelines for the use of these cameras to obtain accurate results. They noted that firstly the camera should be used on a dry surface. Ideally the measuring distance should be 100 cm and the thermal range should be locked at 25℃–30℃. These authors note that this technique has become their favored one for identifying vascular perforators, allowing them the freedom to design a free-style perforator flap [
4]. We decided to follow these parameters for our measurements.
The protocol for this study and informed consent were approved by an institutional review board, in our case the health and disability ethics committees (HDECS) Ethics Approval Committee, and all subjects gave informed consent: all ethics approvals for any studies have been approved by the relevant authorities: New Zealand Health and Disability Ethics Committees (HDEC Reference number 15/CEN/113); Australia: Queensland Institutional Human Ethics (Approval No. 2015001550).
We know from the manufacturers of FLIR one that the palette of colors exhibits the following pattern: the coldest areas are displayed in blue, the hottest areas in white, with red and yellow in between [
5]. We also know from previous studies that the venous temperature is usually higher than the temperature in the artery [
6]. And when it comes to tumors and heat conduction through the surrounding tissue, the tumor heat reaches the skin surface or it is transported indirectly with the venous blood flow to the skin [
6]. Therefore venous perforators are hotter than arteries in the legs, we would expect the veins to display a whitish palette and this was what we noted.
A total of 23 cases formed part of this study—most of the lesions, 16 were pretibial lesions, 4 were located closer to the ankle and 3 were located on the calf. We found the use of thermal imaging camera technically easy and with insignificant user-variation. It was easy to identify thermal patterns for venous perfusion (whiteness) and arterial suffusion (redness) as noted in a case where a fasciotomy had been performed (
Fig. 1). What was immediately apparent was the remarkable consistency of venous perforator ‘islands’ on the lower limb—we noted them in three particular locations that corresponded with previously noted locations of perforator clusters in the lower limb.
We marked out the regions proximally from the inter-malleolar line and venous perforators were shown to be concentrated in certain segments (
Fig. 2). The first cluster was at 5–10 cm from the inter-malleolar line that corresponded with known locations of anterior tibial artery perforators that originate between the tibia and tibialis anterior muscle. Anteriorly, the main larger cluster was at 20–25 cm proximal to this inter-malleolar line, and this corresponds with perforators that originate via the anterior peroneal septum, between the extensor digitorum longus and the peroneus longus muscles (
Fig. 2). Posteriorly on the calf, there was a cluster at 13–18 cm—corresponding with known perforators from the peroneal artery that course through the posterior peroneal septum and these are indicated in the image (
Fig. 3).
We must note that in using this technique, like the use of handheld Dopplers or ultrasound, there is a degree of operator experience required, knowing the optimum imaging distance; however, parameters are easier to define here in this case, and the results were both consistent and reproducible. We set out of mark out ‘perforator islands’ as a guide for cutaneous surgeons. We essentially have mapped locations of blocks of tissue with adequate venous perfusion that could be utilized for island flaps.
We did not set out to identify specific perforators, which we believe is not achievable consistently. However, as noted in the image (
Fig. 4) operators have successfully used this to raise island flaps such as the Bezier Island Flap incorporating venous perforators. In the image (
Fig. 4) the red dot is the tumor and the white islands are the perforators of the flap from the donor side of the Bezier flap.
In studying vascular disorders, many authors have noted the equivalence between thermography and hand-held Dopplers [
7].