An indentation apparatus for evaluating discomfort and pain thresholds in conjunction with mechanical properties of foot tissue in vivo

Abstract

Abstract-The mechanical properties of human foot tissue in vivo as well as discomfort and pain thresholds are important for various applications. In this study, an apparatus for measuring the discomfort and pain thresholds and the mechanical properties of human tissues is presented. The apparatus employs a stepper motor that controls the indentation speed, as well as a load cell and potentiometer that determine the corresponding reaction force and tissue deformation (displacement), respectively. A LabVIEW program (LabVIEW 8, National Instruments Corporation; Austin, Texas) was developed to control the indentation via a data acquisition card. The apparatus can accommodate indentor displacements up to 35 mm and can impart forces up to 150 N at a controlled indentation speed in the range of 0 to 10 mm/s. Tests showed that the displacement measurement error is 0.17 mm in the nominal range (0.5% in the full scale) and the measurement error of force is 1.6 N in the nominal range (1.1% in the full scale). Experimental results indicate that the apparatus is reliable and flexible for measuring the mechanical properties of foot tissue in vivo in conjunction with pain and discomfort thresholds.

Pressure thresholds and stiffness on the plantar surface of the human foot

“…However, previous studies reported a PPT of about 1100 kPa at the heel of young Chinese adults (Rodrigo et al, 2013;Xiong et al, 2010). Again, such a difference may be a reflection of the higher thresholds in the population tested.…”

“…Even though we evaluated the thresholds at 95 points, the clustering indicates that testing five points can reveal the behavior of the plantar foot surface due to similarities across locations. Thus, the points chosen by Rodrigo et al, (2013) and Xiong et al, (2010) are justified.…”

“…However, these offer very little control in terms of the speed and orientation of application. Hence, the Automatic Tissue Tester (ATT) (Rodrigo et al, 2013;Xiong et al, 2010) was used at an indentation speed of 1 mm/s with a 0.5 cm 2 cylindrical, rounded-edge probe. The grid spacing on the template was about 1 cm and the 0.5 cm 2 (or 7.9 mm diameter) probe avoided any interaction between testing points due to their distance from each other.…”

“…The grid spacing on the template was about 1 cm and the 0.5 cm 2 (or 7.9 mm diameter) probe avoided any interaction between testing points due to their distance from each other. A speed of 1 mm/s was used so that the results could be compared to other studies such as Xiong et al, (2010) and Rodrigo et al, (2013). The participants were requested to indicate the PDT and PPT by pressing the appropriate button on the hand-held control panel.…”

“…Researchers have evaluated various objective and subjective properties on the plantar surface of the foot (Aerts and De Clercq, 1993;Cavanagh et al, 1984;Challis et al, 2008;Gonzalez et al, 1999;Hurn et al, 2014;Kinoshita et al, 1992;Rodrigo et al, 2013;Xiong et al, 2010). Unfortunately, there is no way to compare the results of these studies except at the common anatomical landmarks that the researchers have used.…”