title: Macroscopic and histologic evaluation of a rat model of chronic rotator cuff tear.
abstract: BACKGROUND
  The major cause of rotator cuff tears in humans is thought to be tendon degeneration. Although some studies have reported chronic rotator cuff tear models in animals, few studies of chronic rat models have demonstrated persistent defects for a relatively long time. The purpose of this study was to establish a chronic rotator cuff tear model in the rat and to evaluate the model macroscopically and histologically.
  
  
  METHODS
  Sixty Sprague Dawley rats were divided into 2 groups: tendon detachment only (tear group) and tendon detachment plus figure resin (chronic group). The contralateral shoulder served as a sham-operated control (sham group). In the tear group, the supraspinatus and infraspinatus tendons were completely detached. In addition to cuff detachment, figure resin was placed on the greater tuberosity to prevent cuff reattachment and scar formation in the chronic group. Macroscopic and histologic changes were assessed at 4 and 12 weeks after surgery.
  
  
  RESULTS
  A full-thickness cuff defect was observed in all chronic-group rats at both 4 and 12 weeks after surgery, and it could be repaired secondarily by traction in lower tension. However, no cuff defects were observed in the tear group because of obvious scar tissue formation. On histologic evaluation, progressive tendon degeneration, muscle atrophy, and fatty infiltration were observed in the chronic model at 12 weeks after surgery.
  
  
  CONCLUSIONS
  We established a rat model of chronic rotator cuff tears using figure resin. This chronic rotator cuff tear model might be useful for further clinical investigations of rotator cuff repair.
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan. Electronic address: eiko1014@hotmail.com.
authors.forename: Eiko
authors.initials: E
authors.lastname: Hashimoto
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Nobuyasu
authors.initials: N
authors.lastname: Ochiai
authors.affiliation: Department of Orthopedic Surgery, Kitasato University School of Medicine, Kanagawa, Japan.
authors.forename: Tomonori
authors.initials: T
authors.lastname: Kenmoku
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Yu
authors.initials: Y
authors.lastname: Sasaki
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yamaguchi
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Takehiro
authors.initials: T
authors.lastname: Kijima
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Sasaki
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Ohtori
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Takahashi
mesh_terms: D017667:Adipocytes / Q000473:pathology; D000818:Animals; D002908:Chronic Disease; D023421:Models, Animal; D009133:Muscular Atrophy / Q000473:pathology; D017207:Rats, Sprague-Dawley; D000070636:Rotator Cuff Injuries / Q000473:pathology*; D000267:Tissue Adhesions / Q000473:pathology
keywords: Rat; animal model; chronic rotator cuff tear model; fatty infiltration; histologic evaluation; macroscopic evaluation; muscle atrophy; tendon degeneration