Characteristics of Sonography in a Rat Achilles Tendinopathy Model: Possible Non-invasive Predictors of Biomechanics

Su-Ya Lee,Li-Chieh Kuo,Chien-Ju Lin,Hsiao-Feng Chieh,I-Ming Jou,Fong-Chin Su,Po-Ting Wu,Yung-Nien Sun

doi:10.1038/s41598-017-05466-y

Su-Ya Lee, Li-Chieh Kuo + Show 6 more

Open Access

https://doi.org/10.1038/s41598-017-05466-y

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Abstract

The purpose of this study was to investigate the dynamic changes of histopathology, biomechanical properties, echo intensity, and ultrasound features in a collagenase-induced tendinopathy model of rat Achilles tendons, and to examine the associations among biomechanical properties, echo intensity, and ultrasound features. Forty-two rats received an ultrasound-guided collagenase injection on their left Achilles tendons, and needle puncture on the right ones as the control. At four, eight, and twelve weeks post-injury, the tendons were examined via measurements of their biomechanical properties, histopathological and ultrasonographic characteristics. The injured tendons showed significantly higher histopathological scores, lower Young’s modulus, and higher ultrasound feature scores than the those of control ones throughout the study period. Up to week 12, all injured tendons showed defective healing. The neovascularization score had a significant negative linear association with the failure stress and Young’s modulus. Maximum normalized echo intensity had a significant positive linear association with maximum strain. Therefore, neovascularization and maximum normalized echo intensity are associated with mechanically altered tendinopathic tendons. Non-invasive ultrasound methodology, including echo intensity and ultrasound feature scores, may provide useful information about biomechanical properties of tendinopathic tendons.

Highlights

Tendinopathy is the most common soft tissue injury[1], but its pathogenesis remains unclear
We investigated the dynamic changes of histopathology, biomechanical properties, echo intensity, and US feature scores in the collagenase-induced tendinopathy model, and examined the associations among the biomechanical properties, echo intensity, and US feature scores
No US or echo intensity features were associated with the biomechanical parameters for the control tendons. This is the first study to evaluate the dynamic changes in the histopathology, biomechanical properties, echo intensity, and US feature scores in a collagenase-induced tendinopathy model

Summary

Introduction

Tendinopathy is the most common soft tissue injury[1], but its pathogenesis remains unclear. US findings, including focal hypoechogenicity, tendon calcification, and neovascularization, have been reported to be correlated with the severity of tendinopathy[8,9,10] As such, these US feature scores have been applied as a reliable tool for quantifying such abnormalities in tendinopathy[11], but are regarded as essential parameters in animal models[12]. We hypothesized that, in a collagenase-induced tendinopathy model of the rat Achilles tendon, US feature scores and echo intensity would be associated with biomechanical properties. We investigated the dynamic changes of histopathology, biomechanical properties, echo intensity, and US feature scores in the collagenase-induced tendinopathy model, and examined the associations among the biomechanical properties, echo intensity, and US feature scores

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