# A Novel Method for Assessing Regional Tendon Stiffness and Its Significance
## 4 Discussion
[PERSON] et al., 2006, noticed that the vastus medialis oblique (VMO) muscle had fibers attaching to the medial half of the patellar tendon [19]. In the present study, when the patella was taped in a laterally displaced position, increases in tension of the medial retinaculum or/and the vastus medialis oblique muscle might have led to an increase in tendon shear modulus of the medial half of the patellar tendon. Noting that the fibers of the VMO are running horizontally to the patellar tendon, its effect would be greater with the patellar tendon running vertically. Hence, subjects with smaller q-angles might have greater increases in tendon shear modulus than those with larger q-angles. The differential increase in tension at the medial and lateral half of the tendon might have induced a sheer force at the interface between the medial and lateral part of the tendon. This might have had consequences for tendon health. When the patella was displaced medially, the patellar tendon became more oblique. An increase in tendon shear modulus was expected. The changes reached a statistically significant level in the medial half in female but not male subjects. The non-significant change in male subjects might have been associated with their smaller q-angles compared with female subjects. The non-significant changes in the lateral portion were unexpected. Other factors aside from the position of the patella might have had greater effects on the lateral portion of the patellar tendon stiffness when the patella was medially displaced. Different types of equipment, from the clinically viable to more complex systems, have been developed to estimate tendon elastic properties. The material testing system is the most direct and valid method for assessing in-vitro tendon elastic properties [20; 21]. However, this method cannot be applied in-vivo. [PERSON] et al., 2006, proposed the use of B-mode ultrasound with a dynamometer to measure the elastic properties of human patellar tendon [22]. With this approach, ultrasound imaging was used to track tendon elongation during muscle contraction, while the muscle force was estimated from the dynamometer. This method required a long acquisition time [22]. In addition, the computed stiffness reflected the stiffness of the muscle-tendon-joint complex. Direct measurement of the tendon elastic properties was made possible with ultrasound shear wave elastography [23]. The tendon shear modulus, estimated from the ultrasound shear wave elastography techniques on patellar tendon, had good intra- and inter-rater reliability [4]. In this study, the patella was manually displaced and taped at its displaced position. We did not measure the amount of displacement and assumed that the patella would stay in place. Patellar tilting caused by medio-lateral manipulation was not considered in this study. Further studies could include measurement of patellar displacement and its effects on the modulation of tendon shear modulus. Given the relatively large variability of measurements on the tendon shear modulus, a larger sample might be warranted for further study.