Biomechanical assessment of upright stance in parkinson's disease: a single-subject study.

In order to evaluate the usefulness of biomechanical measures in the clinical assessment of Parkinson's disease, we studied the kinematics of upright stance in a patient with evident fluctuations in clinical state (ON-OFF), which allowed us to optimize experimental control. We determined the total amount of movement and the variability of whole body and body segment kinematics in the vertical, anterior-posterior (A-P), and medial-lateral planes. The total excursion parameter (TEX) represented the co-ordinate path over a 20 s period, and the movement variability parameter (VAR) was calculated based on the standard deviation about the quadratic fit to this path. Discriminant analysis was employed to assess the ability of these parameters to discriminate the patient's clinical state, and statistical reduction of the number of measures was accomplished with a stepwise selection procedure. Measures of shoulder A-P movement and the vertical motion of the centre of gravity (COG) were selected for inclusion in both discriminant functions. The VAR function included only four measures (vertical COG and A-P head, shoulder, and hip), while the TEX function required six measures to discriminate the clinical state. Results obtained with the VAR function were superior to those obtained with TEX, and VAR discriminated the OFF state, a common characteristic of Parkinson's disease, especially well. The results are promising, as the measures appear sensitive to the patient's clinical state even though fluctuation of symptoms was reduced in the latter part of the study by various treatments.