Reproducibility of plantar pressure measurements in patients with chronic arthritis: a comparison of one-step, two-step, and three-step protocols and an estimate of the number of measurements required.

BACKGROUND: Plantar pressure measurement may be a helpful evaluation tool in patients with foot complaints. Determination of dynamic pressure distribution under the foot may give information regarding gait, progress of disorders, and the effect of treatment. However, for these measurements to have clinical application, reproducibility, consistency, and accuracy must be ascertained. We compared the reproducibility of measurements among one-step, two-step, and three-step protocols for data collection in patients with arthritis. In addition, the number of measurements needed for a consistent average was determined for the protocol that was found to be the most reproducible.
METHODS: Twenty patients with foot complaints secondary to arthritis participated in the study. Each patient was tested with a pressure platform system using two of the three testing protocols. Reproducibility of contact time and maximal peak pressure were assessed. Intraclass Correlation Coefficients (ICC) were calculated for measurement results among protocols. In stage two of the study, the number of measurements needed for a consistent average was determined by calculating the first three measurements, the first five measurements, and then all seven measurements for both feet. ICC of three, five, and seven measurements were compared. The two-step protocol (13 patients), which was found in stage one of the study to be the most reproducible, was used for this determination.
RESULTS: Reproducibility was found to be reasonable or good for all three measurement protocols. The mean values of contact time for the one-step protocol were found to be higher than the mean values of contact time for the two-step or three-step protocols in both feet. The differences between the one-step and three-step protocols were statistically significant for the left foot only. The mean peak pressure did not show statistically-significant differences among the three protocols. The one-step and three-step protocols were not used for stage two of the study. Using the two-step protocol, three measurements were found to be sufficient for obtaining a consistent average.
CONCLUSIONS: The results of our study indicated that the one-step, two-step, and three-step protocols of collecting plantar pressure measurements in patients with foot complaints secondary to chronic arthritis were all similar. However, the use of the two-step protocol is recommended over the one-step and three-step protocols; the one-step protocol produced a longer stance phase that did not resemble normal walking and when comparing the two-step and three-step protocols, the two-step protocol was less time consuming and less strenuous for patients with painful feet.