# A Novel Method for Assessing Regional Tendon Stiffness and Its Significance
## 4 Discussion  
Using ultrasound shear wave elastography, the present study aimed to determine the effect of patella position on regional tendon stiffness when the patella was experimentally displaced and taped from its resting position. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Patella Position**} & \multicolumn{2}{c}{**Males**} & \multicolumn{2}{c}{**Females**} \\ \cline{2-5}  & **Lateral Half** & **Medial Half** & **Lateral Half** & **Medial Half** \\ \hline Laterally displaced & 0.29 & 0.17 & 0.47 * & \(-\)0.48 * \\ Medially displaced & 0.01 & \(-\)0.23 & 0.24 & \(-\)0.15 \\ \hline \hline \end{tabular} Note: * \(p\) < 0.05.  
\end{table} 
Table 2: Correlation coefficient between the q-angle and the changes in tendon shear modulus when the patella was laterally and medially displaced from its resting position. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Patella Position**} & \multicolumn{2}{c}{**Shear modulus (KPa)**} & \multicolumn{2}{c}{**Shear modulus (KPa)**} \\  & \multicolumn{2}{c}{**Males (\(n\) = 20)**} & \multicolumn{2}{c}{**Females (\(n\) = 20)**} \\ \cline{2-5}  & **Lateral Half** & **Medial Half** & **Lateral Half** & **Medial Half** \\ \hline Neutral & 242.1 \(\pm\) 92.6 & 293.4 \(\pm\) 85.4 & 281.5 \(\pm\) 131.0 & 303.3 \(\pm\) 121.8 \\ Laterally displaced & 307.9 \(\pm\) 150.9 & 356.6 \(\pm\) 147.4 * & 244.3 \(\pm\) 110.3 * & 341.9 \(\pm\) 155.1 * \\ \hline Neutral & 275.8 \(\pm\) 104.7 & 341.2 \(\pm\) 104.9 & 271.0 \(\pm\) 96.8 & 290.7 \(\pm\) 118.3 \\ Medially displaced & 280.8 \(\pm\) 130.5 & 367.8 \(\pm\) 83.4 & 263.3 \(\pm\) 105.0 & 341.4 \(\pm\) 140.7 * \\ \hline \hline \end{tabular} Note: Analyses were made on patellar tendon shear modulus with the patella at its neutral and displaced positions * \(p\) < 0.05.  
\end{table} 
Table 3: Shear modulus of patellar tendon at its resting and displaced positions. This was the first study exploring how patella position affects the patellar tendon shear modulus (an index of stiffness). The relationship was gender and region specific. The q-angle quantified the angle between the line of force of the quadriceps muscle and the patellar tendon. As reported in previous studies [15], we observed a greater q-angle in females than males. In addition, in the female subjects, the q-angle was positively correlated with the percentage of change in the tendon shear modulus when the patella was displaced and taped laterally. More specifically, a larger q angle was associated with a greater reduction in the tendon shear modulus on the lateral half; and a smaller increase in the shear modulus on the medial half of the patellar tendon. The male subjects exhibited a smaller q-angle, which was not correlated with the changes in tendon shear modulus when the patella was displaced. Hence, gender effects on the patellar tendon orientation may have led to tendon regional-specific adaptation and mechanical responses to patellar movement in the medio-lateral directions. When the patella was laterally displaced, the patellar tendon became less oblique, which might have led to a reduction in tendon shear modulus. In the female subjects, a small but significant (4%) reduction in tendon shear modulus in the lateral half of the patellar tendon was detected when the patella was displaced laterally. Changes in patellar tendon obliquity would have been greater in subjects with greater q-angles. In the above paragraph, we reported the positive association between the q-angle and changes in tendon shear modulus in the lateral half of the patellar tendon. However, an increase in tendon shear modulus in the medial half in females (by 13%) and males (by 17%) was observed. The medial reticulum plays an important role as a medial stabilizer of the patella, especially at low angles and attaches onto the medial border of the patellar tendon. [18]. Increases in tension of the medial retinaculum during lateral displacement of the patella might have increased strain on the medial half of the patellar tendon.