Strain Elastography of Injured Equine Superficial Digital Flexor Tendons: A Reliability Study of Manual Measurements

Abstract

Early diagnosis of tendon injuries and accurate long-term monitoring of the healing process are key for equine veterinarians that use conventional ultrasonography. The development of strain elastography could improve the management of clinical cases. The aim of the study was to assess the intraobserver repeatability and interobserver reproducibility of manual measurements of the colored areas of the tendons within elastograms and to standardize this manual modality by comparing the analysis of the images with ImageJ. Twenty elastograms of the injured superficial digital flexor tendons (SDFTs) of horses were analyzed by two different operators after an acute injury was diagnosed with ultrasonography. Statistical analysis demonstrated excellent intraobserver repeatability (intraclass correlation coefficient, ICC = 0.949) and good interobserver reproducibility (ICC = 0.855) for manual measurements performed with tools available on the ultrasound unit. A good agreement between manual measurements and measurements performed with ImageJ (ICC=0.849) was then demonstrated. Despite its subjectivity, the manual modality proved to be a valid method for analyzing images obtained with strain elastography.

Applicability of ARFI elastography in detecting elasticity changes of the equine superficial digital flexor tendon with induced injury

“…Using ARFI elastography, quantitative values have been described in normal human Achilles tendons, 23 as well as a normal decrease in this stiffness as the patients' age advances 24 . In tendons and ligaments of the palmar portion of the thoracic limb of horses, quantitative values of normal stiffness have also been described, and the SDFT had a mean shear velocity of 7.8 m/s, both in the longitudinal and transverse views 15 …”

“…24 In tendons and ligaments of the palmar portion of the thoracic limb of horses, quantitative values of normal stiffness have also been described, and the SDFT had a mean shear velocity of 7.8 m/s, both in the longitudinal and transverse views. 15 In our study, it was possible to quantitatively determine the mean shear velocity for healthy tendons and ligaments and for SDFT with induced tendinopathy at different times during the healing process.…”

“…Additionally, an increase in thickness was observed in the subsequent 30 days 14 . Similarly, through elastograms obtained by strain elastography, injured SDFTs in horses were shown to be less stiff in their acute phase 15 . However, these techniques do not allow quantitative assessment of shear‐wave velocity (tissue stiffness) and might present greater interobserver interference when compared to the ARFI method 12,13 …”

“…14 Similarly, through elastograms obtained by strain elastography, injured SDFTs in horses were shown to be less stiff in their acute phase. 15 However, these techniques do not allow quantitative assessment of shear-wave velocity (tissue stiffness) and might present greater interobserver interference when compared to the ARFI method. 12,13 The present study aimed to describe the applicability of both qualitative and quantitative ARFI elastography in the identification of stiffness changes in equine SDFT with induced injury during the healing process, as well as adjacent structures: deep digital flexor tendon (DDFT), accessory ligament of the DDFT (AL-DDFT), and proximal aspect and body of the suspensory ligament (SL), facilitating the understanding of the pathophysiological process and aiding in its diagnosis.…”

“…The right forelimb was used as a control (G1). Evaluations were performed at eight timepoints: one before injury (T0) and seven (T1-T7) after injury (3,15, 30, 40, 60, 75, and 90 days post-induction). Tendinopathies were visualized as hypoechoic areas with loss of parallel tendon fiber pattern.…”