Ultrasound elastography: compression elastography and shear-wave elastography in the assessment of tendon injury

Abstract

Ultrasound elastography (USE) is a recent technology that has experienced major developments in the past two decades. The assessment of the main mechanical properties of tissues can be made with this technology by characterisation of their response to stress. This article reviews the two major techniques used in musculoskeletal elastography, compression elastography (CE) and shear-wave elastography (SWE), and evaluates the studies published on major electronic databases that use both techniques in the context of tendon pathology. CE accounts for more studies than SWE. The mechanical properties of tendons, particularly their stiffness, may be altered in the presence of tendon injury. CE and SWE have already been used for the assessment of Achilles tendons, patellar tendon, quadriceps tendon, epicondylar tendons and rotator cuff tendons and muscles. Achilles tendinopathy is the most studied tendon injury with USE, including the postoperative period after surgical repair of Achilles rupture tendon. In relation to conventional ultrasound (US), USE potentially increases the sensitivity and diagnostic accuracy in tendinopathy, and can detect pathological changes before they are visible in conventional US imaging. Several technical limitations are recognised, and standardisation is necessary to ensure repeatability and comparability of the results when using these techniques. Still, USE is a promising technique under development and may be used not only to promote an early diagnosis, but also to identify the risk of injury and to support the evaluation of rehabilitation interventions. KEY POINTS: • USE is used for the assessment of the mechanical properties of tissues, including the tendons. • USE increases diagnostic performance when coupled to conventional US imaging modalities. • USE will be useful in early diagnosis, tracking outcomes and monitoring treatments of tendon injury. • Technical issues and lack of standardisation limits USE use in the assessment of tendon injury.

Keywords: Elastography; Sonoelastography; Tendinopathy; Tendon injury; Ultrasound.

Fig. 1

Basic physical principle of compression elastography (CE). The operator exerts compression on the tissue, generating a displacement (δ) that can be estimated by comparing the structure at rest and under compression. The strain (ε) is the ratio difference in displacement between two points to their distance pre-compression (L). The strain measurements are displayed as a colour map, called an elastogram, which is overlaid on the B-mode image. Typically, low strain (stiff tissue) is displayed in blue and high strain (soft tissue) is displayed in red

Fig. 2

Basic physical principle of shear-wave elastography (SWE). A perpendicular stress force (acoustic radiation force) is applied to the tissue, which causes the generation of shear waves. The velocity of the shear wave could be measured by obtaining radiofrequency images with a high frame rate, which can be used to generate a tissue displacement map. Tissue displacements are used to calculate the shear-wave velocity (V_s) and shear modulus (G)

Fig. 3

Images of a normal Achilles tendon using CE and histological correlation. a Conventional ultrasound (US) image of the middle portion of the Achilles tendon in the longitudinal plane. The star indicates the homogenous fibrillar pattern defining normal tendon appearance. b Image of ultrasound elastography (USE) at the same level as in a. The blue-green area of ​​the elastogram represented by the star indicates tissue stiffness where biopsy was subsequently performed. c Histological image obtained with orcein staining showing parallel collagen fibrils, without adipose infiltration and capillary proliferation. Reproduced, with permission, from Klauser et al. [31], copyright (2013) by the Radiological Society of North America, Inc. (RSNA)

Fig. 4

Images of an Achilles tendon with tendinopathy using CE and histological correlation. a Conventional US image of the insertion of the Achilles tendon in the longitudinal plane. The asterisks indicate the hypoechoic area without tendon thickening. CAL: calcaneus. b Image of USE at the same level as a. The red area of ​​the elastogram represented by asterisks is indicative of anomalous decrease of stiffness where biopsy was subsequently performed. c Histological image obtained with azan staining showing loss of the parallel fibrillar structure of the collagen, loss of fibre integrity (asterisks), adipose infiltration (circles), capillary proliferation (plus) and mucoid deposition (star). Reproduced, with permission, from Klauser et al. [31], copyright (2013) by the Radiological Society of North America, Inc. (RSNA)

Fig. 5

CE in the evaluation of the common tendon of the lateral epicondyle. a USE image of the common extensor tendon in the longitudinal plane in a healthy individual. The tendon insertion is shown to have a rigid homogeneous structure (arrows). b (a) The B-mode conventional US image of the extensor tendon in the longitudinal plane. High-grade tendinosis is seen with fibre dehiscence (yellow arrows). At the same level, Doppler (b) demonstrates hypervascularisation and the elastogram (c) shows pathological decrease of the common extensor tendon stiffness. c (a) B-mode conventional US image of the common extensor tendon in the longitudinal plane demonstrating bulging and thickening of the insertion (white arrows). At the same level, the elastogram (b) shows irregular stiffness, involving the peritendinous fascia (black arrows), with pathological adhesion between the tendon and the surrounding tissue. LE: lateral epicondyle, RH: radiohead. Reproduced, with permission, from Klauser et al. [26], copyright (2014) by the Radiological Society of North America, Inc. (RSNA)

Fig. 6

Images of supraspinatus tendon using SWE. a Appearance of a normal supraspinatus tendon showing anisotropy (white arrow) due to curvilinear orientation of the tendon. b Corresponding elastogram showing heterogeneous stiffness in the region of anisotropy and absence of measurement in the deepest region in the humeral head (which is expected since it is a high stiffness structure with limited propagation of the shear waves). c Longitudinal elastography by shear waves of the supraspinatus tendon with tendinopathy. An elastographic pattern of disorganisation and heterogeneity is evidenced, in contrast to the more homogenous pattern of a normal tendon (b). Adapted, with permission, from Winn et al. [18], copyright (2016) The Author(s). Published by Baishideng Publishing Group Inc. All rights reserved