The balance control effects on sitting posture induced by lumbosacral orthosis wear vary depending on the level of stability.

This study aimed to assess the differential impacts of lumbosacral orthosis (LO) wear in different sitting conditions through posturographic measurements. Twelve healthy subjects sat on a force platform with three variable stability levels (stable and on seesaws with a long and short radius, inferring slightly and highly unstable sitting, respectively) and three orthosis conditions (no LO, neutral LO, lordotic LO). Using fractional Brownian motion modelling of the centre of pressure (CoP) displacements, it appears that a stable sitting position did not highlight any particular differences between the LO models. With the lordotic LO, a slightly unstable sitting position decreased the mean time by 72% (p < 0.002) before postural corrective mechanisms took over. In contrast, in highly unstable sitting conditions, the lordotic LO induced larger CoP displacements (increasing variance by 162%, p < 0.038). Thus, depending on the amount of perturbation and the device design, wearing an LO may have a neutral, positive or negative impact on postural control in the sitting position.