## 4 Discussion  
In the present study, the aim was to determine whether clinical leg parameters (leg alignment and femoral parameters) were different in patients with unilateral hip OA and could be correlated to the altered hip and knee adduction moments. These results could help to better understand the initiation and progression of hip OA and the initiation of knee OA in hip OA patients. In the last decade, the EOS system has been proven to be a reliable system for the determination of lower limb length and angle measurements [25], with lower radiation exposure in a weight-bearing position. In the present study, except for FMA, no differences were found in leg parameters between the involved and non-involved legs of hip OA patients and healthy controls. As in the present study, [PERSON] et al. [4] found significant differences in the FMA and other pelvic parameters in OA patients; however, they could not conclude whether these differences were degenerative over time or were inherent differences between the individuals, or whether they contributed to the progression of OA. The orientation of the axis of the femur (FMA) might become important when planning a knee replacement. Although the risk for contralateral knee OA is higher in patients with a unilateral hip replacement for end-stage OA, the ipsilateral knee is not spared [32; 33]. [PERSON] et al. [34] found a reduced NSA in their hip OA patients compared to the healthy controls and suggested that it might be due to the younger age of the healthy controls, as the NSA decreased over time. However, our patients showed a similar NSA to the healthy controls and to the controls of the study of [PERSON], despite the significant age differences. Another study found similar values for the femoral offset and the HKA, but a significantly higher NSA in hip OA patients [35]. However, these patients were measured with standard radiography, whereas the present study used EOS images. The present study confirmed that patients with unilateral hip OA showed a deviating gait pattern compared to healthy controls walking at a similar walking speed. Regarding joint loading, \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** & \begin{tabular}{c} **First Coefficient of** \\ **Determination** \\ \end{tabular} & \begin{tabular}{c} **Second Coefficient** \\ **of Determination** \\ \end{tabular} & \
\begin{tabular}{c} **Third Coefficient of** \\ **Determination** \\ \end{tabular} &
\begin{tabular}{c} **Multiple** \\ **Regression** \\ \end{tabular} \\ \hline KAM1 & FO * & HKA * & Pelvic\_Drop * & \multirow{2}{*}{\(R^{2}\) = 38.6} & \multirow{2}{*}{\(Rm^{2}\) = 77.6} \\  & \(R^{2}\) = 47.1 & \(R^{2}\) = 45.7 & & \\ KAM2 & FO * & & & \\  & \(R^{2}\) = 49.91 & & & \\ HAM1 & Hip\_Add1 * & Pelvic\_Drop & & \\  & \(R^{2}\) = 57.9 & \(R^{2}\) = 30.5 & & \\ HAM2 & Hip\_Add2 * & Knee\_Ext & & \\  & \(R^{2}\) = 53.6 & \(R^{2}\) = 31.1 & & \\ \hline \hline \end{tabular}  
* Statistically significant (\(p\) \(\leq\) 0.05) contribution that caused \(Rm^{2}\) to change due to the inclusion of the new predictor. Abbreviations- maximum external adduction moment for the knee and hip in the first half of the stance phase (KAMI, HAM1) and the second half of the stance phase (KAM2, HAM2); femoral offset (FO); hip–knee angle (HKA); minimal pelvic obliquity in the frontal plane during the swing phase of the contralateral leg (Pelvic\_Drop); maximum hip adduction during the first (Hip\_Add1) and second (Hip\_Add2) halves of the stance phase; maximum knee extension (Knee\_Ext).  
\end{table} 
Table 6: Coefficients of determination (\(R^{2}\) values (%)) for the external joint moments of the involved side as a function of the single correlating leg alignment or kinematic gait analysis parameters and coefficients of determination (\(Rm^{2}\) values (%)) fitted as a function of all the significantly contributing parameters.