Forward flexion of trunk in Parkinson's disease patients is affected by subjective vertical position

No method has been established to evaluate the dissociation between subjective and objective vertical positions with respect to the self-awareness of postural deformity in patients with Parkinson's disease (PD). The purpose of this study was to demonstrate, from the relationship between an assessment of the dissociation of subjective and objective vertical positions of PD patients and an assessment based on established PD clinical evaluation scales, that the dissociation regarding vertical position is a factor in the severity of the forward flexion of trunk (FFT).

Subjects were 39 PD patients and 15 age-matched healthy individuals (control group). Posture was evaluated with measurement of FFT angle during static standing and the subjective vertical position (SV) of the patient. For evaluation of motor function, the Modified Hoehn & Yahr scale, Unified Parkinson's Disease Rating Scale (UPDRS), 3-m Timed Up and Go Test (TUG), and Functional Reach Test (FRT) were used.

In PD patients, FFT angle in the 3rd tertile of patients was 13.8±9.7°, significantly greater than those in the control group and the 1st and 2nd tertiles of PD patients (control group vs 3rd tertile, p = 0.008; 1st tertile vs 3rd tertile, p<0.001; 2nd vs 3rd tertile, p = 0.008). In multiple regression analysis for factors in the FFT angle, significant factors were SV, disease duration, and the standard deviation of each SV angle measurement.

The dissociation between SV and objective vertical position affects the FFT of PD patients, suggesting an involvement of non-basal ganglia pathologies.