I have to declare that in my clinical practice, I do not use ultrasound to image the patellar or achilles tendon – I use MRI imaging in combination with expert musculoskeletal radiologists – so perhaps I have a bias in feeling that US is often used to demonstrate a clinical suspicion and is very very user dependent. I would also always argue that specialists use specialist skills and in my view a radiographer/sonographer delivers optimal imaging, as it is his/her day job and the skill set and exposure and experience – along with appropriate job training and assessment, but still the radiographer doesn’t attempt to make a diagnosis and effect treatment – ‘jack of all trades’ are not well placed in medicine – but I appreciate it is widely applied in a speciality or specialities seeking establish a place.
A combination of B-mode and power Doppler ultrasonography (US) is generally the first-line imaging examination in patients suspected of having Achilles tendonopathy, due to its wide availability and low cost. However, the diagnostic accuracy of this approach remains controversial. Magnetic resonance imaging is an effective alternative, but neither US nor MR imaging provides information on the viscoelastic properties of the tendon.
Real-time shear-wave elastography (SWE) is a recent development whose principle is based on the measurement of shear-wave velocity generated by the US pulse. When used in isotropic soft tissues, this technique makes it possible to evaluate tissue elasticity. Although real-time strain elastography provides qualitative data regarding tissue stiffness on color elastograms, SWE allows further quantitative evaluation of the viscoelastic properties of the tissues.
Recently, the quantitative values of shear-wave velocity for the normal AT were reported. It was also confirmed that stiffness increased when the AT was stretched, and that shear-wave velocity values were higher when the measurements were taken parallel to the fibers as opposed to perpendicular to the fibers because of tendon anisotropy. However, the changes in the viscoelastic properties of unruptured AT have not yet been investigated.
The aim of this study was to investigate the potential changes in the viscoelastic properties of pathologic versus normal ATs by using real-time SWE.
Eighty healthy volunteers (median age 50 years, range 31–57 years) and 25 patients (median age 56 years, range 46–63 years) were included. Among the patients, 20 had unilateral and five had bilateral tendonopathy, all confirmed at US. Altogether, 180 US and SWE studies of ATs without tendonopathy and 30 studies of the middle portion of the AT in patients with tendonopathy were assessed prospectively.
All examinations were performed bilaterally according to a standardized protocol with a US system equipped with a 12-MHz superficial linear transducer. The examination began with gray-scale B-mode and power Doppler US to evaluate AT morphology. The width and thickness of each AT were measured, the cross-sectional area of each AT was calculated. The presence of a fusiform enlargement of the AT, consistent with tendonopathy, and an interruption of AT fibers focally replaced by a hypoechoic or anechoic region consistent with a tear in the tendon were noted. Measurements in the elastographic mode were made successively for two passively mobilized ankle positions: maximal plantar flexion (position 1, relaxed) and 0° flexion (position 2, stretched). The mean shear-wave velocity was measured in the SWE mode. This was used to calculate the relative anisotropic coefficient. The presence of a signal-void area on elastograms was also noted.
ATs that showed midportion tendonopathy had significantly lower mean velocity than did normal ATs at axial SWE for position 1, at sagittal SWE for position 2, and at axial SWE for position 2. Receiver operating characteristic curve analysis was used to define mean velocity thresholds below which tendonopathy was assumed. In patients with unilateral tendonopathy, mean velocity was significantly lower in ATs with tendonopathy than in the contralateral ATs at sagittal SWE for position 1.
Tendon softening was a sign of tendonopathy in relaxed ATs when the mean velocity was less than or equal to 4.06 m/sec at axial SWE (sensitivity, 54.2%; specificity, 91.5%) and less than or equal to 5.70 m/sec at sagittal SWE (sensitivity, 41.7%; specificity, 81.8%) and in stretched ATs, when the mean velocity was less than or equal to 4.86 m/sec at axial SWE (sensitivity, 66.7%; specificity, 75.6%) and less than or equal to 14.58 m/sec at sagittal SWE (sensitivity, 58.3%; specificity, 83.5%).
Regardless of the position and orientation of the SWE acquisition, there was no significant difference in the relative anisotropic coefficient between ATs with tendonopathy and normal ATs or between unilateral tendonopathy and normal contralateral ATs.
Six partial-thickness tendon tears were detected at B-mode US. They appeared as a signal-void area on the color SWE elastogram in which the mean velocity could not be measured.
The authors concluded that pathologic tendon softening encountered at the midportion of the Achilles tendon in patients with tendonopathy can be assessed quantitatively with realtime SWE and this may be helpful for diagnosis and evaluation of the severity and healing of tendonopathy. Tendon softening assessed by using SWE appeared to be highly specific, but sensitivity was relatively low. SWE may be useful to detect partial-thickness tears and confirm complete tendon rupture.