Identification of a voluntary overcontrol of postural sway from static stabilometric assessment.

OBJECTIVE: When subjects present medically unexplained postural instability, a voluntary overcontrol of postural sway is often suspected. Aphysiologic postural imbalance may be detected in dynamic conditions on a servo-controlled platform (Equitest), but it remains difficult to objectify from static stabilometric evaluation. Our objective was to identify the key stabilometric parameters that allow to discriminate subjects with voluntary postural instability, control subjects and neurological patients with organic postural instability.

MATERIAL/PATIENTS AND METHODS: Stabilometric data from 41 control subjects, 21 voluntarily simulating postural instability, were compared with those from 173 neurological patients with postural instability (stroke, spinal cord injury, Parkinson's disease, cerebellar syndrome) and with data from 3 patients suspected to simulate postural instability. Data were obtained in static condition of bipodal support, with open and closed eyes. The studied parameters were: velocity of center of pressure (velocity-CP), area of the 90% confidence ellipse of statokinesigram (area-SKG) and number of peaks greater than 0.2 (NP2) on the curve of cross-correlations between anteroposterior and mediolateral displacements of CP.

RESULTS: Eyes open, high values of the velocity-CP (72.3±36.3mm·s(-1)), NP2 (4.9±2.4) and area-SKG (13 015±10 667mm(2)) were observed in controls simulating instability, comparable to those of 3 patients suspected to simulate postural instability (velocity-CP: 15-131mm·s(-1), NP2: 3-9, area-SKG: 1117-6675mm(2)) and higher than those of neurological patients (velocity-CP: 16.8±10.1mm·s(-1), NP2: 1.3±1.1, surface-SKG: 385.7±436.9mm(2); P<0.05). Similar results were obtained with eyes closed.

DISCUSSION-CONCLUSION: Several stabilometric parameters obtained in static conditions seem relevant to identify aphysiologic postural instability related to a voluntary overcontrol of postural sway, while allowing to distinguish such subjects from patients with postural instability of neurological origin.