Influence of Podal Sensory Information on Static and Locomotion, Using Foam and Orthopaedic Insoles

The foot is a fundamental area of interaction with the environment. To understand and quantify the importance of plantar information for balance control, researchers characterized plantar sensors and evaluated the motor adaptations induced by disrupting the sensory feedback of this information via different techniques: electrostimulation, vibration, anesthesia, mechanical stimulation (Bent, 2015). Mechanical stimulation is non-invasive and uses material of different characteristics. In most cases, it is a foam plate or an orthopedic insole (composed of predefined reliefs).

In clinical practice, the foam is used to assess the foot ability to adapt to the correction of the orthopedic insoles. A patient stands still on a force plate which records Center of Pressure (CoP) position. The CoP oscillations with and without the foam are compared using the Plantar Quotient (PQ). PQ is the ratio between the oscillation surface of the CoP on the foam and the oscillation surface of the CoP without foam. A podal postural inefficiency is then defined by a PQ >100% meaning that their balance is improved with the interposition of a foam. However, there is no consensual characteristics about the height or the density of the foam.

In addition, postural evaluation with mechanical stimulation was previously done exclusively in this static mode, which does not represent an ecological reality of daily life activities. The effect of thin orthopedic elements has never been quantified during a locomotor task.

In this context, our project has two objectives, that will be addressed through two experimental studies. The first objective is to relate the effect of foam characteristics and postural stability. Understanding the standard postural response will allow to identify patients with a podal postural inefficiency. The second objective is to evaluate the effect of a sole element on the statics and locomotion of healthy participants compared to ineffective podal postural participants (determined via the calculation of the PQ detailed previously with the foams analyzed in the first study).

We will perform clinical tests carried out in a daily podiatry practice adding motion capture to consider dynamic situations more precisely. The study is interventional (non-invasive) and non-permanent due to the interposition of thin foam plate (less than 1 cm thick) and sole elements (3 mm thick) under the feet.