[Effects of rigid-ankle and ankle-foot orthoses in the control of asymetrical undisturbed upright stance].

Objective: To limit sensorimotor impairment associated with various diseases, devices aimed at easing such impairment are usually prescribed. A better knowledge of the specific effects of these devices in healthy subjects should help to assess the prescription.

Materials And Methods: Sixteen young healthy individuals were required to stand still on a double-force platform with an asymmetrical body weight distribution over the 2 legs and to reduce as much as possible their motions. Four conditions (1 used as reference without any orthosis and 3 with an ankle orthosis and 2 soft [ORP-S] and rigid [ORP-R] ankle-foot orthoses) were performed randomly. For each condition, 6 repetitions lasting 32 s were recorded. The centre-of-pressure trajectories from the loaded (CP(Cha)) and unloaded (CP(Déc)) feet and the resulting displacements (CP(Res)) were then computed along both the mediolateral (ML) and anteroposterior (AP) axes. Finally, these trajectories were analysed by their mean positions and parameters (Root Mean Square and Median Frequency) aimed at characterising their frequency spectra.

Results: Wearing the ORP-R model resulted in a backward shift of the mean position of the CP(Déc) trajectories, which had repercussions on CP(Res) values. In addition, frequency analysis showed decreased RMS for only the CP(Déc).

Discussion-conclusion: We found effects linked to the physical features of various ankle orthoses tested. These effects can be observed because of the separate measure of the unloaded support. This data should improve the prescription of ankle-foot orthoses according to patient needs. These results should be viewed as a first step before their extension to study of patients with hemiparalysis, to improve their prescription in accordance with such patients' needs.