Sonographic evaluation of the effect of long-term exercise on Achilles tendon stiffness using shear wave elastography

Objectives: This study aimed to assess the feasibility of using quantitative shear wave elastography (SWE) to assess the stiffness (Young's modulus) of Achilles tendon and to investigate the effect of long-term weight-bearing exercise on the stiffness of human Achilles tendon by comparing the frequent and infrequent exercise groups. Design: Case-control study. Methods: A total of 36 healthy subjects aged 19-25 were recruited. Subjects were categorized into frequent and infrequent exercise groups dependent on their level of lower limb weight bearing exercise. B-mode and shear-wave ultrasound examination of Achilles tendon were performed. Measurements of the Achilles tendon stiffness were conducted with the foot position standardized by an ankle fixer. To evaluate inter and intra-operator reliability of Young's modulus measurements, each subject was scanned by three operators and each operator scanned the subject three times. Results: The intra-operator reliability of Young's modulus measurements ranged between 0.803 and 0.845. The inter-operator measurement reliability was 0.585. Result showed that Achilles tendon on non-dominant ankle in frequent-exercisers (median: 320.1 kPa) was significantly stiffer than that in infrequent-exercisers (median: 296 kPa)(p < 0.05), whereas there was no significant difference in Achilles tendon stiffness on dominant ankle between the two groups (p > 0.05). Conclusions: Shear wave elastography is feasible for assessing the Achilles tendon's stiffness in vivo. The stiffness of Achilles tendon of frequent-exercisers was significantly higher than that of infrequent exercisers on non-dominant ankle but not on dominant ankle. With the use of an ankle fixer, there was high repeatability and moderate reproducibility in SWE measurement of Achilles tendon stiffness. (C) 2016 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.