Accuracy and repeatability of a semi-quantitative barefoot pressure measurement method for clinical use: The Derks...

This study was designed to assess the accuracy and repeatability of the Derks Calculation Method in the normal foot during walking.

Measurements were taken from 25 healthy subjects (age 32.0 ± 12.4), 23 females and 2 males, on five separate occasions at seven days, three weeks, three months, and nine months apart by means of a mid-gait method. Values were calculated for internal rotation (IR) and external rotation of the heel (ER), heel valgus/varus (HV), heel length (HL), heel width (HW), width of the midfoot (WM) and the forefoot (WF), and the length of the foot (LF).

For all five separate occasions and in 87.5% of the parameters investigated, the coefficient of repeatability (CR, expressed as a percentage of the mean) was less than 5%. One parameter showed a high CR - heel valgus/varus (HV) was extremely high (>800%). The maximum 95% Confidence Interval (CI) for the five different occasions was no higher than 0.2 cm for IR, ER and HV with a standard error (SE) of 0.01 and >0.01 respectively. The maximum 95% CI for WF was 0.4 cm (SE 0.1), and for HW, WM and LF the maximum 95% CI was 0.7 cm (SE 0.1 or 0.2). HL showed the highest 95% CI (0.9 cm) with an SE of 0.2.

The Derks Calculation Method was found to be accurate and repeatable if HV was excluded, which renders this method a viable clinical tool in settings where sophisticated computerised systems are still unavailable.