## 4 Discussion  
The present study aimed to quantitatively assess postural abnormalities on the sagittal plane in Parkinson's disease patients by 3D motion analysis using an accurate whole-body marker set (DB-Total protocol); moreover, the impact of the treatment with the K1 Posture Keeper shirt on the sagittal posture during upright standing and walking was investigated. As reported in previous studies [44, 47], marked anteflexion of the thoracolumbar spine on the sagittal plane causes the forward shift of the center of pressure. This could limit the ability of the individual to respond to balance perturbations and could lead to reduced postural stability and increased risk of falls and back pain [4, 15]. Indeed, sagittal postural alterations, encompassing anterior trunk flexion, camptocormia, and antecollis, have been identified as disabling conditions in PD [15]. However, given the reversibility of PD-associated postural abnormalities, the use of adjustable orthoses might allow the straightening of the trunk, improving the whole-body sagittal alignment with positive effects on postural stability in both static and dynamic conditions in PD patients with anteflexion of the thoracolumbar spine and/or anterior bending of the neck. To the best of our knowledge, this is the first study to quantitively evaluate by 3D motion analysis the effect of treatment with a corrective corset (K1 Posture Keeper) in both static and dynamic conditions in PD patients with sagittal misalignment according to the MDS Task Force Consensus [13]. Figure 6: Boxplot of significant differences (\(p\)-value \(\leq\) 0.05) for average of kinematic parameters in multiple comparisons implemented via repeated measures–ANOVA. Figure Notes: Significant differences are highlighted in bold (“\(\ast\ast\)”\(p\)\(<\) 0.05, \"\(\ast\ast\ast\)\"\(p\)\(<\) 0.01). T0 without K1 (A); T0 with K1 (B); T1 without K1 (C); T1 with K1 (D); (**a**) C7-nasion (CNA), (**b**) S2-C7-occiput (SCO) and (**c**) heel-ascrum-nasion (HSN) angles; degree (Deg). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Score**} & \multicolumn{6}{c}{**QUEST Questionnaire Answer**} \\ \cline{2-9}  & \multirow{2}{*}{**Dimension**} & \multirow{2}{*}{**Weight**} & \begin{tabular}{c} **Facility of** \\ **Regulation** \\ \end{tabular} & \
\begin{tabular}{c} **Stability** \\ **and Safety** \\ \end{tabular} & \multirow{2}{*}{**Durability**} & \multirow{2}{*}{**Easy to Use**} & \multirow{2}{*}{**Comfort**} &
\begin{tabular}{c} **Efficacy of** \\ **the Effect** \\ \end{tabular} \\ \hline Mean & 4.25 & 4.91 & 4.66 & 4.75 & 4 & 5 & 4.41 & 4.83 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Mean value of QUEST questionnaire scores (range from 1 to 5 points) across participants. Demographic data are presented in Table 1, showing a prevalence of male subjects (69,2%) in the PD population and underlining a slightly larger prevalence of anterior trunk flexion with thoracic fulcrum (60%) associated to a larger prevalence of antecedlis (80%) that occurred in the upright standing position. Moreover, 40% of the PD patients presented camptocormia with thoracic fulcrum. These findings, revealed by clinical examination executed via NeuroPostureApp, showed postural abnormalities with anterior sagittal bending at head-cervical region and an anterior trunk flexion at thoracic level. The comparison of 3D-motion analysis parameters between the healthy and PD populations during upright standing (Table 2) showed a significant increase in the C7-nasion-angle (CNA) and a significant decrease in the S2-C7-occipt (SCO) angles in PD patients, confirming the abnormal anterior position of the head with respect to the trunk and, in particular, of the nasion with respect to C7 and of the occipt with respect to C7 and sacrum. Moreover, the significant increase in cervical tilt (CT) angle revealed a flexion of the head with respect to the trunk in PD patients (Table 2; Figure 4a).