## 3 Results and Discussion
The clinical parameters consist in the functional test of the Clinical Frailty Scale (CFS) index and the Oxford questionnaire (using the scale 1 to 5 of feeling experiencing activities of daily living during the past 4 weeks) that includes four measures Q4, Q6, Q11, and the total Oxford score, which reflects the severity of problems that the patients have with their knee. The kinematic parameters comprise only those of the sagittal plane: flexion angle at initial contact (\(X_{13}\) and \(X_{48}\)) and the end of terminal stance phase (\(X_{25}\)), and minimum flexion/extension angle during the loading phase, the stance phase, the stance and early swing phases, and during the gait cycle. The functional test of CFS (\(Y_{42}\)) and the Q4 Oxford Question (\(Y_{10}\)) have the largest positive correlations with the kinematic parameters in the sagittal plane. \begin{table}
\begin{tabular}{c|c|l} \hline
**Clusters** & **Variables** & **Characteristics** \\ \hline \multirow{6}{*}{C1} & & Absolute variation in tibial rotation between the end of loading phase \\  & X67 & and heel strike \\  & X51, X52, X19 & Flex/Ext total range of motion, absolute value of the Flex/Ext angle, \\  & & Flex/Ext angle. \\  & Y38 & Index joint Ext: knee extension range of motion (ROM) \\  & Y37 & Index joint Flex: knee flexion ROM \\ \hline \multirow{6}{*}{C2} & X13 & Flexion angle at heel strike (at initial contact) \\  & X48 & Absolute value of flexion angle at heel strike \\  & X25 & Flexion angle at the end of terminal stance phase \\  & X49 & Absolute value of the minimum Flex/Ext angle during loading phase \\  & X22 & Minimum Flex/Ext angle (Min Flex/Ext) during the gait cycle \\  & X20, X23 & Min Flex/Ext during stance phase, Min Flex/Ext during stance and early swing phases \\  & Y42 & Frailty Index: Clinical Frailty Scale (CFS) \\  & Y10 & Q4 OKS: For how long have you been able to walk before pain becomes severe? \\  & Y12 & Q6 OKS: Have you been limping when walking, because of your knee? \\  & Y17 & Q11 OKS: Could you do the household shopping on your own? \\  & Y19 & Total Oxford Score \\ \hline \multirow{2}{*}{C3} & X46 & Internal/external tibial rotation angle at the end of push-off phase \\  & Y3 & BMI \\ \hline \end{tabular}
\end{table} 
Table 2: Clusters of correlations between the variables \(X\) and \(Y\). The third cluster C3 relates the internal/external tibial rotation angle at the end of push-off phase and the BMI by a considerable positive correlation (near the inner circle of correlation with a cut-off = 0.5 in Figure 1). Finally, the between cluster analysis shows that the correlation between the clinical variables in cluster C1 and the kinematic variables in cluster C2 are strongly negative. The same statement is observed for the correlation between the clinical variables in cluster C2 and the kinematic variables in cluster C1. Moreover, the correlations are negligible between the third cluster C3 and the other two clusters (C1 and C2). As explained above, the angle between each pair of clusters (C1, C3) and (C2, C3) is apparently right, so that the correlation is almost null. The correlation analysis is expanded to a higher level of threshold. Figure 4 shows a cross-correlation variable representation by relevance networks with a cut-off = 0.40. We notice that only one subset (of few variables) remains important with higher correlation level. The number of correlated variables is reduced for the most important clinical parameters \(Y_{38}\) (in cluster C1) strongly correlated with nine kinematic parameters (in clusters C1 and C2). This analysis shows that increasing the threshold value establishes the most important correlated parameters. However, it leads to the loss of certain correlations that remain significant. The analysis of correlation between kinematic features of gait waveform data and clinical parameters has been, basically, done using a univariate correlation analysis [9; 10; 11; 12].