Observations on the F-Scan in-shoe pressure measuring system

BACKGROUND:: F-Scan (Tekscan Inc.) is a commercial in-shoe force/pressure measurement system. The system has been used in a number of useful clinical studies focused mainly on the evaluation of various therapeutic measures including footwear and in-shoe orthoses. More recently, the accuracy and reliability of the system has come under closer scrutiny, highlighting the need for further debate supported by experimental studies. We have critically evaluated the performance of the F-Scan sensor and report here on bench test findings examining calibration error, hysteresis and creep, and the accuracy and repeatability of output force measurements. METHOD:: The F-Scan system was used to measure output mass following calibration using the standard protocol across a range of subject determined input masses. A small jig-mounted force meter was used to test groups of individual sensing units (4 @ cm(2)) for within and between sensor accuracy in full size and adjusted sensors. An Instron servohydraulic materials testing unit was used to evaluate creep, hysteresis and the repeatability of output forces over repeated loading cycles for full size and cut sensors. RESULTS:: Average calibration error: 4% Creep: 19% Hysteresis: 21% [Table: see text] CONCLUSION:: 1. The F-Scan calibration protocol is inaccurate. 2. Significant within and between sensor variability in output forces can be expected. 3. The creep and hysteresis properties of the sensor are poor. 4. The F-Scan sensor does not yield repeatable measurements. 5. When the sensor is adjusted to a smaller size output is adversely affected. The F-Scan system has a limited capability for absolute accuracy but may be used for quantitative studies provided its limitations are noted.