Letter to the Editor: “Clinical applicability of shear wave elastography for the evaluation of medial epicondylitis”

by Yi-Hsiang Chiu, Ke-Vin Chang (kvchang011@gmail.com)

Clinical applicability of shear wave elastography for the evaluation of medial epicondylitis

Dear Editor-in-Chief,

We read with great interest the recently publication in European Radiology by Bang et al [1]. The study retrospectively collected 61 elbows in 54 patients, and compared the diagnostic performance of strain and shear wave sonoelastography in patients with and without medial epicondylitis. The results disclosed that patients with medical epicondylitis had lower strain ratios and shear wave velocity measured by sonoelastography. Besides, there was no difference between strain and shear wave sonoelastography in diagnostic performance for medial epicondylitis. We acknowledge the authors for their efforts in employing sonoelastography to evaluate medial epicondylitis. Herein, we would like to humbly comment the use of strain sonoelastography on tendon stiffness.

In this paper, the strain ratio of the common flexor tendon at the medial epicondyle were smaller than 1 (0.48 in patients with medial epicondylitis and 0.95 in patients without medial epicondylitis in Table 1 of the article). However, the authors did not detail how the strain ratio was calculated, which is strongly related to the interpretation of tissue stiffness [2]. Since tissue compressibility is positively correlated with tissue strain, a harder structure has a smaller strain value [2]. The value of the strain ratio may be positively or negatively associated with tissue stiffness, depending on the tissue strain of which area has been treated as the numerator or denominator. In this study, the shear wave velocity in the tendinopathic area was lower than that in the normal region, indicating an increase in softness in the pathological part. Therefore, the strain value of the pathological area should be larger than that of the normal region. As the strain ratio presented in this study was less than 1, we speculate that the strain ratio was derived the strain value of the normal region divided by that of the target/pathological area. Unlike the shear wave velocity, an increase in the strain ratio cannot be simply represent an increase in tissue stiffness. We believe it is better to elaborate how the strain ratio is calculated in the session of methodology.