title: Structure of retracted tendons after staged repair following continuous traction.
abstract: OBJECTIVE
  The effect of staged repair involving continuous re-lengthening of the retracted musculotendinous unit after rotator cuff tear is not known. We quantified changes in chronically retracted tendons undergoing no repair or a staged repair involving an initial re-lengthening of the musculotendinous unit by traction in a sheep model of massive rotator cuff tear.
  
  
  METHODS
  Infraspinatus tendons of 12 sheep were released and allowed to retract for 4 months. Repair was performed after the retracted musculotendinous unit had been progressively returned to its original length through continuous traction in 8 sheep (group I). In the other 4 sheep (group II) traction was not successful and the tendons remained retracted. Tendon structure was assessed macroscopically, by MRI, histology, and TEM.
  
  
  RESULTS
  Normalized to their contralateral controls, at sacrifice, tendon thickness was unchanged in group I (116%, n.s) and increased in group II (129%, P < 0.05), however with substantial shortening. Increased collagen fiber crimping and disorganization was found in group II, whereas in group I the differences from normal tendon were less pronounced.
  
  
  CONCLUSIONS
  Retracted musculotendinous units have deteriorated tendons, characterized by increased collagen fiber crimp, and ultrastructural collagen fibril atrophy and disorganization. Continuous traction may arrest and partially restore degenerative changes in retracted tendon. The findings of this study might contribute to new approaches for the treatment of chronic "irreparable" rotator cuff tears.
authors.affiliation: Department of Orthopedics, University of Zürich, Balgrist University Hospital, Forchstrasse 340, 8008, Zürich, Switzerland. mazda.farshad@balgrist.ch
authors.forename: Mazda
authors.initials: M
authors.lastname: Farshad
authors.forename: Christian
authors.initials: C
authors.lastname: Gerber
authors.forename: Jess G
authors.initials: JG
authors.lastname: Snedeker
authors.forename: Thomas
authors.initials: T
authors.lastname: Frauenfelder
authors.forename: Dominik C
authors.initials: DC
authors.lastname: Meyer
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D008279:Magnetic Resonance Imaging; D008853:Microscopy / Q000379:methods; D017006:Rotator Cuff / Q000473:pathology / Q000601:surgery*; D000070636:Rotator Cuff Injuries; D012756:Sheep; D013536:Suture Techniques; D013710:Tendons / Q000473:pathology / Q000601:surgery*; D014143:Traction