Validity and repeatability of three in-shoe pressure measurement systems

- We compared three commercially available in-shoe pressure measurement systems.
- Variables were repeatability and validity for whole insole and regional held loads.
- All systems compared displayed high between day repeatability for all variables.
- Pedar displayed the highest validity for pressure and Medilogic for contact area.
- When evaluating clinical risk from in-shoe pressure the Pedar system is recommended.

In-shoe pressure measurement devices are used in research and clinic to quantify plantar foot pressures. Various devices are available, differing in size, sensor number and type; therefore accuracy and repeatability. Three devices (Medilogic, Tekscan and Pedar) were examined in a 2 day × 3 trial design, quantifying insole response to regional and whole insole loading. The whole insole protocol applied an even pressure (50-600 kPa) to the insole surface for 0-30 s in the Novel TruBlue™ device. The regional protocol utilised cylinders with contact surfaces of 3.14 and 15.9 cm2 to apply pressures of 50 and 200 kPa. The validity (% difference and Root Mean Square Error: RMSE) and repeatability (Intra-Class Correlation Coefficient: ICC) of the applied pressures (whole insole) and contact area (regional) were outcome variables. Validity of the Pedar system was highest (RMSE 2.6 kPa; difference 3.9%), with the Medilogic (RMSE 27.0 kPa; difference 13.4%) and Tekscan (RMSE 27.0 kPa; difference 5.9%) systems displaying reduced validity. The average and peak pressures demonstrated high between-day repeatability for all three systems and each insole size (ICC ≥ 0.859). The regional contact area % difference ranged from −97 to +249%, but the ICC demonstrated medium to high between-day repeatability (ICC ≥ 0.797). Due to the varying responses of the systems, the choice of an appropriate pressure measurement device must be based on the loading characteristics and the outcome variables sought. Medilogic and Tekscan were most effective between 200 and 300 kPa; Pedar performed well across all pressures. Contact area was less precise, but relatively repeatable for all systems.