## 4 Discussion  
The aim of this study was to determine the association between PTFJ morphology and knee alignment. Abnormal knee alignment may induce OA symptoms [20]. Therefore, investigating association the between PTFJ morphology and knee alignment is important. The most important findings from the present study were as follows: (1) There were significant differences between the varus FTA group, the normal FTA group, and the valgus FTA group in terms of shape type, inclination of the PTFJ, declination of the PTFJ, and relative articular height. (2) The valgus group was associated with a higher relative articular height and a smaller declination angle of the PTFJ in comparison to the varus FTA group. The varus FTA group had a significantly higher ratio of trochoid types, higher inclination angle, and higher relative articular height than both the valgus group and normal group. However, a study by [PERSON] et al. [8] reported no significant difference in relative articular height between varus knees and valgus knees. This difference could be due to the use of the hip-knee angle (HKA) to represent knee alignment in [PERSON]'s study, thus having different criteria for determining varus and valgus knees. In this study, knee alignment (varus, neutral, or valgus) was related to PTFJ morphology in declination angle and relative articular height in the logistic regression model. However, the results were inconsistent with [PERSON] et al. [8], in which no significant correlation was found between the relative articular height and knee alignment. This inconsistency may be explained by differences in the regression methods. In our study, a multinomial logistic regression analysis was used, while [PERSON] et al. used linear regression. The different group criterion mentioned previously may also have contributed. Figure 3 shows the relative position of a fibula to a tibia. This construct is used to explain the biomechanical relationship between these bones and their importance to knee alignment. The weight-bearing force on the fibula (\(F_{f}\)) generates a valgus moment (M) on the knee joint which, depending on the magnitude of the moment, could induce a valgus deformation. The more proximally a fibula is positioned (higher relative articular height), the larger the moment arm of the fibula (\(l\)) is. This can increase the valgus moment, subsequently leading to valgus deformation. However, if the fibula is located posteriorly relative to the tibia (larger declination angle), the moment arm of the fibula is shorter, as \begin{table}
\begin{tabular}{c c c c c c c c} \hline \multirow{2}{*}{**Groups**} & \multirow{2}{*}{**Variables**} & \multicolumn{3}{c}{**Unadjusted Model**} & \multicolumn{3}{c}{**Adjusted Model \({}^{*}\)**} \\ \cline{3-8}  & & **OR** & **95\% CI** & \(p\)**-Value** & **OR** & **95\% CI** & \(p\)**-Value** \\ \hline \multirow{4}{*}{Normal FTA Group} & Shape Type & 1.327 & (0.592, 1.402) & 0.336 & 1.620 & (1.509, 1.902) & 0.226 \\  & Articular Surface Area & 1.832 & (1.781, 1.923) & 0.782 & 1.891 & (1.892, 1.923) & 0.382 \\  & Inclination of PTFJ & 0.317 & (0.245, 0.423) & 0.019 & 0.463 & (0.124, 0.582) & 0.092 \\  & Relative Articular Height & 0.828 & (0.681, 0.952) & 0.092 & 0.305 & (0.102, 0.491) & 0.107 \\  & Declination of PTFJ & 1.506 & (1.362, 1.759) & 0.083 & 1.487 & (1.273, 1.717) & 0.061 \\ \hline \multirow{4}{*}{Valgus FTA Group} & Shape Type & 1.201 & (0.231, 1.927) & 0.398 & 1.293 & (1.018, 1.632) & 0.527 \\  & Articular Surface Area & 1.832 & (1.781, 1.923) & 0.109 & 1.891 & (1.892,1.923) & 0.194 \\ \cline{1-1}  & Inclination of PTFJ & 0.572 & (0.230, 0.981) & 0.820 & 0.326 & (0.108, 0.796) & 0.719 \\ \cline{1-1}  & Relative Articular Height & 0.547 & (0.129, 0.831) & 0.034 & 0.608 & (0.205,0.998) & 0.017 \({}^{*}\) \\ \cline{1-1}  & Declination of PTFJ & 0.307 & (0.095, 0.759) & 0.020 & 0.632 & (0.601,0.887) & 0.019 \({}^{*}\) \\ \hline \end{tabular} \({}^{*}\) Adjustment for age, gender, and BMI.  
\end{table}