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 subjects. Methods Evaluation of the posture included measuring FFT, the angle of lateral flexion of trunk, and the angle at the position that the subject 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.