ASSOCIATION BETWEEN PLANTAR TEMPERATURE INCREASE AND PLANTAR SHEAR STRESSES IN HEALTHY SUBJECTS

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. 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): Sites of increased plantar temperature have been suggested to indicate plantar loading in previous investigations. However, this idea has not been successfully validated. The purpose of this study was to determine if a linear relationship existed between walking-induced increases in plantar temperature and measured plantar stresses. Significant relationships between the two variables would suggest thermographs to be an effective tool used to assess plantar tri-axial and/or shear loading, potentially leading to significant advancements in the study of biomechanical factors related to the diabetic amputations. Methods (b): Thirteen healthy participants were recruited, and informed consent was obtained prior to the study. Pre-exercise baseline plantar temperature profiles were measured with the use of an infrared thermal camera. Participants were then asked to walk on a custom-built platform that was used to measure tri-axial plantar stress distributions. Subjects then walked barefoot on a treadmill for 10 minutes. Post-exercise temperature distribution was measured and recorded. After all data were collected, sites of increased peak temperature and peak stress for each foot were documented. The frequency in which the two different sites matched was determined. In addition, increased peak temperature values were correlated against plantar stress magnitudes. Results (c): Peak temperature increase site matched the location of peak shear in 23% of participants. Peak temperature increase site also occurred at the peak resultant stress site in 39% of participants. A significant correlation was found between the magnitudes of temperature increase and peak shear (R = 0.78, p = 0.02). Conclusions (d): A moderate linear relationship was established between peak plantar temperature increase and the horizontal component of plantar stresses. It may be useful to explore a potential non-linear association between these two variables. If a non-linear relationship can be modeled, predicting plantar shear may be possible. The ability to predict plantar shear could allow for assistance in assessing the risk of ulcer development in the diabetic foot and subsequent amputation. Thermographs are still not a reliable source for the prediction of shear, but our initial results warrant further investigation.