Use of Plantar Pressure Sensors to Take Weight-Bearing Foot Casts

Abstract

Techniques of taking casts mainly rely not on the objectivity of the procedure, but on the experience and skill of the technician. The aim of this study was to demonstrate the efficiency of a technique of taking standing foot casts controlled via pressure sensors. In this way, we mean to objectivize the degree of correction. The study was carried out through 150 procedures on 50 feet of 29 patients. The value of the "Heel Symmetry Index" was calculated on three casts in three different situations of the same foot: A first cast in which the subject did not control the position of his/her foot; a second cast where manipulations corrected the foot's pronator position; and a third cast with pressure sensors placed in the subject's heel. This enabled the control and quantification of the pressure during the manipulation when taking the cast. The comparison of the "Heel Symmetry Index" in the different groups showed significant p-values of 0.05. Conclusion: The technique of taking casts controlled by pressure sensors achieved more equilibrated casts with a better symmetry index of the heel's outline.

Keywords: foot cast; foot mold; foot orthosis; heel symmetry; insole.

Figure 1

Placing the sensors in the places chosen.

Figure 2

Taking the standing cast with pressure sensors.

Figure 3

Cast taking moment with sensors and pressure reading, observing on the graph the reading of a single line when the pressures equalize (in that moment, the pressure registered by 3, 5 and 7 sensors are the same).

Figure 4

Cut of the cast in the zone of the heel.

Figure 5

Processing for the measurements of the distinct points of the curve and to determine its symmetry index. 10 coordinates were estimated in each half heel from −10 to +10, beside symmetry “Y” axis (yellow line). For example: (X10, Y10) coordinates were determined measuring the distance of X10 on X axis, and the high of Y10 (h(X10)) on Y axis. For each foot, 20 coordinates were determined, 10 in each half of the heel. The sum of this coordinates is included in the equation.

Figure 6

Box plot of the “Symmetry heel” values according to the three variables of the study.