CLINICAL VALUE OF TEMPERATURE IN ASSESSING FOOT LOADING IN DIABETIC PATIENTS WITH AND WITHOUT NEUROPATHY

Unnoticed repetitive plantar stresses are believed to cause diabetic foot ulcers. In severe cases, the development of these foot ulcers can lead to lower extremity amputations. The measurement of vertical plantar pressure has previously been used to predict where ulcers may develop, but was eventually determined to be a poor predictor of these occurrences. Shear is an additional element of plantar stresses that has not been thoroughly investigated due to the lack of available stress platforms with the capability of measuring the horizontal component stresses. In a limited number of studies higher shear stresses have been found in diabetic patients. Previous investigations have implemented the use of plantar temperature profiles in an attempt to develop an alternative method for determining plantar loading. Increases in temperature were seen and may have been a result of friction from plantar shear forces according to these reports. However, the potential relationship between temperature and shear has not been investigated thoroughly. If significant associations can be determined between the location and magnitude of both peak shear and temperature, researchers and clinicians may develop a better understanding of diabetic foot ulcer formation which could potentially lead to improvements in therapeutic footwear. Purpose (a): Diabetic ulcers lead to an estimated 100,000 amputations every year in the United States. Ulcers are known to have a biomechanical etiology that relates to three dimensional ground reaction forces/stresses. Among these stresses, horizontal shear stress cannot be easily quantified. It was hypothesized that plantar temperatures can estimate shear loading of the foot. The purpose of this study was to explore a site-wise association between peak plantar temperature and peak pressure and shear stresses obtained from diabetic patients using a thermal camera and custom-built pressure-shear plate. If confirmed, thermographs can assist clinicians/researchers in preventing diabetic ulcer related amputations. Methods (b): Two groups, each consisting of 14 diabetic patients with neuropathy (DN) or without neuropathy (DC), were recruited for the study after informed consent was obtained. Resting foot sole temperatures were recorded using an infrared thermal camera. Subjects walked on a 12 ft. walkway that accommodated the stress plate. Stress variables such as peak pressure (PP), peak shear (PS), peak pressure integral time (PTI) and peak shear-time integral (STI) were recorded from five regions of the foot (i.e., hallux, lesser toes, first metatarsal head (1st MTH), central forefoot (2nd and 3rd MTH) and lateral forefoot (4th and 5th MTH)). Results (c): Pearson correlation analysis between each stress variable against temperature were statistically significant (p<0.05) in both groups. The r values ranged between .405 and .511. Despite significant correlation results, peak temperatures could not successfully identify peak stress locations in group DN (14-57%). Success rates were higher for the DC group (50-86%). Conclusions (d): The potential association between plantar stresses and temperature is thought to have a complicated and non-linear relationship. Appropriate modeling schemes can be implemented to explore such relationships. Thus our results warrant further investigation on this topic.