title: Altered patterns of displacement within the Achilles tendon following surgical repair.
abstract: OBJECTIVE
  Ultrasound speckle tracking was used to compare tendon deformation patterns between uninjured and surgically repaired Achilles tendons at 14-27-month follow-up. The hypothesis was that the non-homogenous displacement pattern previously described in uninjured tendons, where displacement within deep layers of the tendons exceeds that of superficial layers, is altered following tendon rupture and subsequent surgical repair.
  
  
  METHODS
  In the first part of this study, an in-house-developed block-matching speckle tracking algorithm was evaluated for assessment of displacement on porcine flexor digitorum tendons. Displacement data from speckle tracking were compared to displacement data from manual tracking. In the second part of the study, eleven patients with previous unilateral surgically treated Achilles tendon rupture were investigated using ultrasound speckle tracking. The difference in superficial and deep tendon displacement was assessed. Displacement patterns in the surgically repaired and uninjured tendons were compared during passive motion (Thompson's squeeze test) and during active ankle dorsiflexion.
  
  
  RESULTS
  The difference in peak displacement between superficial and deep layers was significantly (p < 0.01) larger in the uninjured tendons as compared to the surgically repaired tendons both during Thompson's test (-0.7 ± 0.2 mm compared to -0.1 ± 0.1 mm) and active dorsiflexion (3.3 ± 1.1 mm compared to 0.3 ± 0.2 mm). The evaluation of the speckle tracking algorithm showed correlations of r ≥ 0.89 between displacement data acquired from speckle tracking and the reference displacement acquired from manual tracking. Speckle tracking systematically underestimated the magnitude of displacement with coefficients of variation of less than 11.7%.
  
  
  CONCLUSIONS
  Uninjured Achilles tendons display a non-uniform displacement pattern thought to reflect gliding between fascicles. This pattern was altered after a mean duration of 19 ± 4 months following surgical repair of the tendon indicating that fascicle sliding is impaired. This may affect modulation of the action between different components of the triceps surae, which in turn may affect force transmission and tendon elasticity resulting in impaired function and risk of re-rupture.
authors.affiliation: Division of Orthopaedics and Biotechnology Karolinska University Hospital, Department of Clinical Sciences Intervention and Technology (Clintec), Karolinska University Hospital, Karolinska Institute, Huddinge, 141 86, Stockholm, Sweden. asa.froberg@ki.se.
authors.forename: Åsa
authors.identifier: http://orcid.org/0000-0001-9246-7318
authors.initials: Å
authors.lastname: Fröberg
authors.affiliation: Division of Orthopaedics and Biotechnology Karolinska University Hospital, Department of Clinical Sciences Intervention and Technology (Clintec), Karolinska University Hospital, Karolinska Institute, Huddinge, 141 86, Stockholm, Sweden.
authors.forename: Ann-Sophie
authors.initials: AS
authors.lastname: Cissé
authors.affiliation: School of Technology and Health, KTH Royal Institute of Technology, Huddinge, Sweden.
authors.forename: Matilda
authors.initials: M
authors.lastname: Larsson
authors.affiliation: School of Technology and Health, KTH Royal Institute of Technology, Huddinge, Sweden.
authors.forename: Mattias
authors.initials: M
authors.lastname: Mårtensson
authors.affiliation: SICS, Swedish ICT Research Institute, Kista, Sweden.
authors.forename: Michael
authors.initials: M
authors.lastname: Peolsson
authors.affiliation: Division of Orthopaedics and Biotechnology Karolinska University Hospital, Department of Clinical Sciences Intervention and Technology (Clintec), Karolinska University Hospital, Karolinska Institute, Huddinge, 141 86, Stockholm, Sweden.|Department of Clinical Science and Education, Södersjukhuset, Karolinska Institute, Stockholm, Sweden.
authors.forename: Tomas
authors.initials: T
authors.lastname: Movin
authors.affiliation: Division of Orthopaedics and Biotechnology Karolinska University Hospital, Department of Clinical Sciences Intervention and Technology (Clintec), Karolinska University Hospital, Karolinska Institute, Huddinge, 141 86, Stockholm, Sweden.|The Swedish School of Sports and Health Sciences, Stockholm, Sweden.
authors.forename: Anton
authors.initials: A
authors.lastname: Arndt
mesh_terms: D000125:Achilles Tendon / Q000000981:diagnostic imaging* / Q000601:surgery*; D000465:Algorithms; D000818:Animals; D001696:Biomechanical Phenomena; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging; D016059:Range of Motion, Articular; D012421:Rupture / Q000503:physiopathology; D013552:Swine; D014463:Ultrasonography
keywords: Achilles tendon; Deformation pattern; Rupture; Speckle tracking; Surgical repair