Combined Assessment of 2-D Ultrasound and Real-Time Shear Wave Elastography of Low-Intensity Pulsed Ultrasound Therapy Efficacy in Rabbits with Achilles Tendinopathy.

Objective: Low-intensity pulsed ultrasound (LIPUS) has been gradually used to treat Achilles tendinopathy. However, there are limited non-invasive and efficient instruments for monitoring LIPUS efficacy in Achilles tendinopathy. The purpose of this study was to assess the therapeutic effectiveness of LIPUS after Achilles tendinopathy by 2-D ultrasound and real-time shear wave elastography (SWE).

Methods: Ninety New Zealand white rabbits were divided into control, sham and LIPUS groups after tendinopathy modeling. On days 1, 4, 7, 14 and 28, the Achilles tendon thickness and SWE Young's modulus on the long axis were measured. The tissues of the Achilles tendon were then evaluated histologically.

Results: The mean SWE values increased while the average thickness and histologic scores decreased, especially in the LIPUS group (9.5% and 80.7% on day 28, respectively). The SWE values in the LIPUS group were significantly lower than those in the control group on day 1 (121.0 kPa vs. 177.6 kPa) and peaked on day 7 (173.7 kPa, p < 0.001). By day 28, the SWE value had approached that of the control (191.2 kPa vs. 192.4 kPa), and had been significantly higher than that in the sham group since day 7. SWE values and histologic scores were correlated (r = -0.792, p < 0.01). The average thickness decreased in the three groups but did not differ significantly.

Conclusion: Two-dimensional ultrasound is beneficial to the diagnosis of Achilles tendinopathy. SWE could quantify changes in Achilles tendon stiffness non-invasively during LIPUS treatment, enabling the study of early Achilles tendon healing after LIPUS treatment.