Functional Reach and touch: how sense of movement disorders can influence Anticipatory Postural Adjustment?

Background: Sense of movement disorders (SMDs), as result of the failure of a complex multisensorial process involving the proprioceptive, visual, somaesthetic, and vestibular systems (A Berthoz 1997), are very frequent in children with cerebral palsy (CP) and negatively influence motor function- ing and postural control. The most frequent signs are: exaggerated and low threshold startle reaction, freezing posture, blinking or closing eyes, visual attention shifting, and facial grimaces. Diplegic children with SMDs show panic reactions to mild postural perturbations and are therefore unable to execute common tasks successfully, such as reaching and touching an object. Postural adjustments depend on motor reactions as well as on perception but perception has a leading role in anticipation. Objectives: We wanted to investigate how SMDs negatively influence anticipatory postural adjustments (APA). Method: A group of 14 children with diplegia were selected according to the following criteria: aged 6–15 years, acquired walking, no major differences at GMFCS, and no major sensorial or cognitive deficit. Eight were diagnosed positive for SMDs (according to the mentioned clinical signs), six did not have SMDs, and five normal participants matched for age were selected for the control group. The experimental setting consisted of a functional reach and touch task in the sitting position on an adjustable stool, a force platform registered the centre of pressure. A small ball target was placed at a distance of 120% of arms’ length and at 45˚ of abduction. The child sat with feet on a foot rest. The stool was set at two levels: ground and raised. Results: APAs are indicated by a backward shifting of centre of pressure with respect to the reaching direction before the start of the gesture. The presence of APAs according to group were: SMD, ground 42%, raised 36%; non-SMD ground 83%, raised 78%; controls, ground 93%, raised 93%. Discussion: The diplegic group with SMD has significantly fewer APAs than both the controls and non-SMD group. The height of the stool seems to influence APAs within the same group but we did not have enough statistical evidence (ttest). Data seem to support the hypothesis that SMDs influence negatively anticipatory postural control and this can reduce autonomy levels in action.