# Ultrasound Elastography in the Evaluations of Tendon-Related Disorders--A Systematic Review
## 4 Discussion  
### Discussion  
To our knowledge, this is the first review focused on ultrasonography and ultrasound elastography in tendon-related disorders. We have included studies with a cross-sectional design, which is the most appropriate and frequent study design used to assess diagnostic accuracy [61]. Ultrasound elastography has been undergoing rapid growth in recent years in terms of use and in the number of publications [62]. Tendinopathy conditions are characterized by a degenerative process that occurs in the long term because of overuse and repetitive stress. Inflammation occurs in the first few weeks as a response to damage to repair and reconstitute the involved tissue. Often the reparative mechanism fails, thus leading to degenerative changes in the collagenous matrix and irregular fiber structure, hypercellularity, hypervascularity, accumulation of fluid between fibers, and a lack of inflammatory cells [63]. In tendinopathy, these pathologic changes occur concurrently with the attempts at tissue repairing (\"degeneration\" and attempts of \"regeneration\"). The presence of disorganization of collagen fibers (normally arranged in a parallel configuration and densely packed) leads to a localized decrease in tendon stiffness. Therefore, stiffness analysis can help in diagnosing tendinopathy [64]. Ultrasound elastography analyzes the elasticity of the investigated tissue through ultrasound. Both ultrasound elastography types (shear wave elastography and strain elastography) can be used to investigate tendon elastic properties, resulting in different measurements. In shear wave elastography, two outcomes can be obtained: shear modulus measured in kPa or shear wave velocity (SWV) measured in m/s. In strain elastography, the outcome is the strain, defined as the amount of displacement from the probe. Knowingthe strain and identifying a reference, the strain elastography software calculates the strain ratio, which is an index of the relative elasticity of an objective region of interest (ROI) and a reference ROI with a constant elasticity [65]. Therefore, it is expected that in cases of tendinopathy, the tendon is \"softer\" and stiffness decreases, with a reduction in shear modulus, in shear wave velocity for the shear wave elastography, and in strain ratio for the strain elastography (higher strain for softer tissues) [66]. In some cases, US elastography analysis provides conflicting results; as shown by [PERSON] [47], [PERSON] [32], and [PERSON] [57], a pathologic patellar tendon (both in athletes and non-athletes) is less elastic (increased stiffness) than controls. The opposite result was obtained by [PERSON] et al. [34] and [PERSON] et al. [54] who showed that symptomatic patellar tendons (both in athletes and nonathletes) have decreased stiffness compared to nonsymptomatic tendons. This finding is in contrast to previous studies but in agreement with what is expected. These contradicting results have already been mentioned by [PERSON] [47], who hypothesized how different methods of image analysis, different ultrasound equipment, and different positions of the knee can be potential explanations for the discordant findings. In particular, it has been mentioned that a more flexed position of the knee leads to increased stiffness. Therefore, a standardized position is required to obtain compatible results. Finally, different US equipment can lead to different results but also different transducers and different acquisition depths [47]. Despite the different results, most of the studies that considered this type of pathology [32; 34; 47; 54] concluded that US elastography significantly improves diagnostic accuracy when used in combination with the conventional US, providing good-to-excellent inter-operator and intra-operator reliability.