Objectives: To study potential differences between sway of the paretic and of the nonparetic pelvis and leg in standing hemiparetic patients by comparing measurements of corresponding bilateral waist and leg sites, and by comparing the results to those of healthy control subjects.
Design and setting: Anterior-posterior and mediolateral sway of 15 hemiparetic patients and 13 healthy control subjects was measured with the eyes open and closed during quiet stance. Data were collected via an ultrasonic-based system that continuously monitored the position of four transducers mounted bilaterally on the anterior aspect of the pelvis and on each tibial tuberosity. Sway of each transducer marker was calculated by the standard deviation around its mean position and by its mean speed. Descriptive statistics, analysis of variance, and cross-correlation analysis were used for comparing hemiparetic patients with healthy subjects, as well as for determining the effects of body level, body side, and vision on postural sway.
Results: For all four measurement sites and in both the anterior-posterior and mediolateral axes, the hemiparetic patients had larger sways than the control subjects. Patients' sway on the paretic side was larger than on the nonparetic side, whereas no side differences were detected in the control subjects. For both groups, waist sway was larger than legs' sway. Cross-correlation values between sway of the ipsilateral waist and leg on each body side, as well as between the two legs, were substantially lower in the patients than in healthy subjects.
Conclusions: Postural sway of standing hemiparetic patients is characterized by an asymmetrical profile that is expressed both in larger sway values of the paretic than of the nonparetic side, and in low temporal synchronization between sway of the legs and of the pelvis as well as between the two legs. Impairment in the ability to stabilize the distal segments of the lower extremity on the paretic side, rather than in stabilization of the pelvis, appears to underlie the enhanced postural sway of hemiparetic patients during stance.