title: Viscoelasticity in Achilles tendonopathy: quantitative assessment by using real-time shear-wave elastography.
abstract: OBJECTIVE
  To investigate the differences in viscoelastic properties between normal and pathologic Achilles tendons (ATs) by using real-time shear-wave elastography (SWE).
  
  
  METHODS
  The institutional review board approved this study, and written informed consent was obtained from 25 symptomatic patients and 80 volunteers. One hundred eighty ultrasonographic (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. Each study included data sets acquired at B-mode US (tendon morphology and cross-sectional area) and SWE (axial and sagittal mean velocity and relative anisotropic coefficient) for two passively mobilized ankle positions. The presence of AT tears at B-mode US and signal-void areas at SWE were noted.
  
  
  RESULTS
  Significantly lower mean velocity was shown in tendons with tendonopathy than in normal tendons in the relaxed position at axial SWE (P < .001) and in the stretched position at sagittal (P < .001) and axial (P = .0026) SWE. Tendon softening was a sign of tendonopathy in relaxed ATs when the mean velocity was less than or equal to 4.06 m · sec(-1) at axial SWE (sensitivity, 54.2%; 95% confidence interval [CI]: 32.8, 74.4; specificity, 91.5%; 95% CI: 86.3, 95.1) and less than or equal to 5.70 m · sec(-1) at sagittal SWE (sensitivity, 41.7%; 95% CI: 22.1, 63.3; specificity, 81.8%; 95% CI: 75.3, 87.2) and in stretched ATs, when the mean velocity was less than or equal to 4.86 m · sec(-1) at axial SWE (sensitivity, 66.7%; 95% CI: 44.7, 84.3; specificity, 75.6%; 95% CI: 68.5, 81.7) and less than or equal to 14.58 m · sec(-1) at sagittal SWE (sensitivity, 58.3%; 95% CI: 36.7, 77.9; specificity, 83.5%; 95% CI: 77.2, 88.7). Anisotropic results were not significantly different between normal and pathologic ATs. Six of six (100%) partial-thickness tears appeared as signal-void areas at SWE.
  
  
  CONCLUSIONS
  Whether the AT was relaxed or stretched, SWE helped to confirm and quantify pathologic tendon softening in patients with tendonopathy in the midportion of the AT and did not reveal modifications of viscoelastic anisotropy in the tendon. Tendon softening assessed by using SWE appeared to be highly specific, but sensitivity was relatively low.
authors.affiliation: From the Department of Musculoskeletal Imaging, University Hospital of Besançon, Besançon, France (S.A., J.P.N.); I4S Laboratory, INSERM EA4268, University of Franche-Comte, Besançon, France (S.A., F.M.); ESPCI ParisTech, CNRS UMR7587, INSERM U979, Institut Langevin Ondes et Images, Paris, France (M.T.); Department of Diagnostic and Interventional Radiology, Lausanne University Hospital, Lausanne, Switzerland (F.B.); Clinical Investigation Center, INSERM CIT808, University Hospital of Besançon, Besançon, France (C.V.); and Department of Neuromuscular Examination and Diseases, University Hospital of Besançon, Besançon, France (F.M.).
authors.forename: Sébastien
authors.initials: S
authors.lastname: Aubry
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Nueffer
authors.forename: Mickaël
authors.initials: M
authors.lastname: Tanter
authors.forename: Fabio
authors.initials: F
authors.lastname: Becce
authors.forename: Chrystelle
authors.initials: C
authors.lastname: Vidal
authors.forename: Fabrice
authors.initials: F
authors.lastname: Michel
mesh_terms: D000125:Achilles Tendon; D000328:Adult; D003199:Computer Systems; D054459:Elasticity Imaging Techniques / Q000379:methods; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D052256:Tendinopathy / Q000000981:diagnostic imaging*