The effect of subjective postural vertical on forward flexed posture in Parkinson's disease

Background: We developed a novel method to measure the angle of subjective postural vertical (SPV) and showed that the SPV may be related to the exacerbation of the forward flexed posture. Objectives: The present study prospectively tested the effects of the subjective postural vertical on the exacerbation of the forward flexion of trunk (FFT) through long-term observation of Parkinson's disease patients. Methods: Evaluation of the posture included measuring FFT, the angle of lateral flexion of trunk, and the angle at the position that the patient subjectively perceived as the vertical position at a stationary upright position immediately after standing up at the time of initial observation, 6 months later, and 1 year later. Results: The SPV angles worsened significantly at 6 months and 1 year compared to the first measurements (9.3 ± 6.7° vs. 10.8 ± 8.2° and 10.6 ± 7.8°, P < 0.05), and the FFT angles worsened significantly at one year compared to the first measurements (11.1 ± 8.1° vs. 12.2 ± 8.8°, P = 0.004). Furthermore, using a hierarchical multiple regression model, the difference in SPV from the first visit to the first half year was considered a factor contributing to annual FFT change (P = 0.002). Conclusions: This longitudinal study of a large number of cases suggested that changes in SPV may precede changes in FFT.