Differential effects of semi-rigid and soft orthoses on postural control between affected and unaffected leg in patients with functional ankle instability in compared with healthy subjects

Postural control deficits after lateral ankle sprain have been shown in patients with functional ankle instability (FAI). Numerous researchers have shown different effects of orthosis on postural control in FAI patients. It seems that the condition of chosen control group might explain the different results obtained from those studies. To the author's knowledge, no study has compared the effect of orthosis on postural control against different control conditions. Twenty patients with functional instability of ankle and twenty were matched healthy subjects participated in the study. Postural control in single limb stance was assessed for both affected and unaffected foot while using soft and semi-rigid orthosis. Standing without using orthosis was considered as the baseline condition. Balance control was evaluated by force platform. Our results showed that interaction between group and orthosis was significant for all of the parameters extracted from center of pressure (COP) data, meaning that orthosis has a differential effect on postural control between the two groups. Also, interaction between foot side and orthosis was not significant for all of the COP parameters. In another words, orthosis has the same effect on involved and uninvolved foot side. Although orthosis improved postural stability in patients with FAI, it showed no such an effect in healthy subjects. As the other finding, it was demonstrated that orthosis has no differential effect on postural control between involved and uninvolved foot side in both groups. Therefore, the positive effects of orthosis on postural control in FAI patients may be revealed when healthy subjects are involved as control group in research design.