## 3 Results
### Inter-Group (Healthy vs. PD Groups) Postural Differences in Upright Standing  
The comparison between the PD and healthy groups showed a significant decrease in the PD group for the following sagittal parameters in upright posture: HSO (t = 2.46; \(p\) = 0.024), HSN (t = 3.29; \(p\) = 0.004), and HSC (U = 23.0; \(p\) = 0.045) (Figure 3(a), Table 2). Instead, a significant increase was found for CNA (t = \(-\)4.20; \(p\) \(\leq\) 0.001) and for CT (t= \(-\)2.46 \(p\)= 0.025) in the PD group compared to the healthy one (Figure 3(a), Table 2). Figure 4: Graphical representation of sagittal whole-body parameters resulted in significant differences in various comparisons: (**a**) healthy versus PD group in upright standing; (**b**) PD group without K1 versus with K1 during upright standing and walking at T0 and T1 (* the asterisk indicates a significant difference only during walking). T0 (before treatment), T1 (after treatment with K1 Posture Keeper). Figure Notes: the black dashed line indicates the vertical axis; the greydashed lines represent head and thoracic planes with their corresponding perpendicular lines. The down and up arrows indicate a significant decrease and increase in parameters, respectively. Nasion (Ns), occupit (O), cervical (C), frontozygomatic suture (FZs), acromioclavicular joint (ACj), sacrum (S), heel (He); C7-nasion (CNA), cervical tilt (CT), S2-C7-occiput (SCO), heel-sacrum-occipit (HSO), heel-sacrum-nasion (HSN), and heel-sacrum-C7 (HSC) angles. Intragroup (PD Patients) Postural Differences in Upright Standing Before and After Treatment with K1 Posture Keeper  
The multiple comparison across four conditions [T0 without (A) and with (B) orthosis and T1 without (C) and with (D) orthosis] in upright standing showed for the PD group a significant effect of the K1 Posture Keeper orthosis on the following sagittal parameters in upright posture: CNA (F = 4.57; \(p\) = 0.011) and SCO (\(\chi^{2}\) = 5.96; \(p\) = 0.049). In particular, a significant decrease in CNA (\(p\) = 0.033) and increase in SCO (\(p\) = 0.045) angles was found in T1 with K1 compared to T0 without K1 (Table 3, Figures 4b and 5). \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Sagittal**} & \multicolumn{1}{c}{**Healthy Group**} & \multicolumn{1}{c}{**Parkinson’s Disease Group**} \\
**Parameter** & **Mean \(\pm\) SD (min, max) or Median (Percentiles 25\%; 75\%)** & \(p\)**-Value** \\ \hline CNA [Deg] & \(52.6\pm 2.77\) (\({}^{49,0,56.3}\)) & 61.2 \(\pm\) 5.80 (\({}^{52.6,68.4}\)) & **\textless{0.001 ***}** \\ \hline CT [Deg] & \(45.6\pm 7.10\) (\({}^{37.6,56.1}\)) & 60.7 \(\pm\) 16.75 (\({}^{37.0,89.8}\)) & **0.025 \({}^{*}\)** \\ \hline DA [Deg] & \(152\pm 5.79\) (\({}^{141,163}\)) & 146 \(\pm\) 6.26 (\({}^{137,160}\)) & 0.078 \\ \hline LA [Deg] & \(196\) (\(195\); \(203\)) & 194 (\(191\); \(197\)) & 0.130 \\ \hline TT [Deg] & \(18.4\pm 7.80\) (\({}^{2.80,25.4}\)) & 24.2 \(\pm\) 6.10 (\({}^{14.20,37.4}\)) & 0.082 \\ \hline STA [Deg] & \(-4.92\pm 3.21\) (\({}^{-9.10,0.00}\)) & \(-7.93\pm 4.77\) (\({}^{-14.50,2.50}\)) & 0.115 \\ \hline SCA [Deg] & \(3.98\pm 2.07\) (\({}^{0.80,7.90}\)) & 5.09 \(\pm\) 2.45 (\({}^{1.60,9.10}\)) & 0.289 \\ \hline SCO [Deg] & \(172\pm 11.0\) (\({}^{152,187}\)) & 163 \(\pm\) 12.3 (\({}^{144,177}\)) & 0.110 \\ \hline HSO [Deg] & \(176\pm 3.17\) (\({}^{172,181}\)) & 171 \(\pm\) 5.91 (\({}^{159,181}\)) & **0.024 \({}^{*}\)** \\ \hline HSN [Deg] & \(161\pm 2.91\) (\({}^{156,166}\)) & 157 \(\pm\) 3.46 (\({}^{152,165}\)) & **0.004 \({}^{**}\)** \\ \hline HSC [Deg] & \(177\) (\(176\); \(179\)) & 175 (\(174\); \(176\)) & **0.045 \({}^{*}\)** \\ \hline HST [Deg] & \(186\pm 3.42\) (\({}^{181,190}\)) & 189 \(\pm\) 4.39 (\({}^{183,198}\)) & 0.165 \\ \hline SVA [mm] & \(31.3\pm 16.2\) (\({}^{6.20,61.5}\)) & 41.6 \(\pm\) 20.9 (\({}^{12.80,70.3}\)) & 0.235 \\ \hline \hline \end{tabular}
\end{table}