In-shoe pressure measurements with a viscoelastic heel orthosis

Abstract

Objective: To detect the mechanical effect of a viscoelastic heel orthosis. Design: Two-factor analysis of variance with interactions between the orthosis and the subjects. The number of subjects was determined by presuming the effect of the orthosis to be twice as large as the error-free standard deviation (SD) of the interactions, the step-to-step SD four times as large as the error-free SD of the interactions, type 1 error probability equal to .05, and type 2 error probability equal to .20. Setting: A gait laboratory in a university hospital. Subjects: Twenty-two consecutive patients with treated heel pain. Main Outcome Measures: Peak pressure (PP), pressure-time integral (PTI), and foot-to-sensor contact time (CoT) measured for five steps at 24 discrete sensors of predetermined positions in the foot with treated heel pain. Results: The orthosis reduced PPs, PTIs, and CoT ( p < .05) in the median midfoot and lateral midfoot; reduced PPs and PTIs ( p < .05) in the posterior heel and medial midfoot; increased PP and PTI ( p < .05) in the anterior part of the first metatarsal head; and increased PTI ( p < .05) in the lateral part of the hallux. The ratios of the estimated step-to-step SDs to the estimated error-free SDs of the interactions of PPs, PTIs, and CoT were less than four at all the sensors. Conclusion: Proper design and estimation of the variations ensured that there was sufficient power to detect the effect of an a priori specified size as statistically significant: the orthosis reduced the mechanical loads in the posterior heel and the midfoot and increased the mechanical loads in the anterior part of the first metatarsal head and the lateral part of the hallux during walking.