# The Thermo-Pressure Concept: A New Model in Diabetic Foot Risk Stratification
## 1 Introduction  
Hospitalisation of a patient with diabetes is more likely to occur as a consequence of foot disease than any other complication [1]. The resulting health care costs in western health systems may account for up to 20% of the total diabetes expenditure [2]. Foot ulceration is a common diabetic foot complication, which most often is a precursor to lower limb amputation. Even though over 80% of diabetic foot ulcers are preventable, 1% of people living with diabetes are still at risk of ulcerating [3]. The prognosis of diabetic foot ulceration (DFU) is poor, with three-year mortality rates after primary amputations thought to be as high as 20-50% [4] and five-year mortality rates after a major amputation are second only to lung cancer [5]. While high plantar pressure is a proposed predictor of diabetic foot ulceration, and different pressure thresholds have been proposed, no fixed and consistent pressure value has been given to quantify this effect [6, 7]. A previous study considered 6 kg/cm\({}^{2}\) (588.6 kPa) as the pressure threshold that can cause soft tissue damage in high-risk patients living with Type 2 Diabetes Mellitus during walking [7]. Indeed, pressures ranging from 200 kPa to 1000 kPa [8] have been proposed as predictive thresholds for ulceration in persons living with DM; specific values include 588 kPa [9] and 335 kPa [10]. It was also suggested that plantar pressure greater than 700 kPa is thethreshold in screening patients who are at risk of developing diabetic foot ulceration [11]; it was also suggested that in the presence of a pre-ulcerative lesion, lack of in-shoe peak pressure below 200 kPa and \"high barefoot dynamic peak plantar pressure\" are risk factors for a pressure-related plantar ulcer [12]. On the other hand, a study [13] reports a peak plantar pressure of 348 kPa in participants living with diabetes for over 10 years and no known complications. Whilst this value exceeds some of the thresholds listed in the literature, none of the participants exhibited any trends towards ulceration. This demonstrates that, on its own, the pressure might not be an ideal model to actually \"predict\" foot ulceration, although it may be the only quantifiable value available to date. The data from a study by [PERSON] et al. support the belief that elevated foot pressure is an important risk factor for foot complications. However, the authors suggest that foot pressure by itself is a poor tool to predict foot ulcers [14]. The current prognostic models rely either solely on measuring temperature, pressure, or some form of shear assessment; these parameters, however, rarely reach 50% specificity in relation to DFU. There is currently very limited evidence that supports the use of single clinical parameters in predicting the risk of DFU [15]. One possible consequence of prolonged plantar pressure on a region of the foot is local ischemia in this region that may precede tissue breakdown. Thermography, the measurement of cutaneous temperature, may be a method of actually detecting these temperature changes since pressure may either reduce cutaneous blood flow, perhaps reducing the local temperature, or indeed raise this temperature if inflammatory changes occur. A study that categorized patients into healthy, healthy diabetic, ischaemic, neuropathic and neuroischaemic groups reported significant foot temperature differences between two groups: a healthy group (comprising healthy and healthy diabetic participants) compared to a complications groups (peripheral arterial disease, neuropathy and neuroischaemic) [16]. These authors hypothesize that through their predictive model, these two groups--healthy and complications--can be identified through thermal imaging. This raises a query that those patients with peripheral arterial disease, where one would predict colder feet, actually exhibited higher temperatures which, however, has been evidenced through two different studies [16; 17].