title: Atrophy of type I and II muscle fibers is reversible in the case of grade >2 fatty degeneration of the supraspinatus muscle: an experimental study in rabbits.
abstract: BACKGROUND
  Although clinical investigations indicate that the limit of reversibility of rotator cuff muscles fibers type I and II atrophy is grade 2 of fatty degeneration (FD) according to the Goutallier computed tomography classification, little is known about the morphometric verification of these findings.
  
  
  METHODS
  The supraspinatus tendon was detached from the greater tubercle and the infraspinatus and subscapularis in 12 rabbits, and a 12-week observation period followed. This proved to be sufficient for development of grade >2 FD of the supraspinatus tendon. The tendon was then reinserted. The animals were euthanized 24 weeks after tendon reconstruction. The sections of middle part of supraspinatus were stained for adenosine triphosphatase reaction, and morphometric measurements were taken of type I and II muscle fiber diameters. The contralateral shoulders served as controls.
  
  
  RESULTS
  The macroscopic inspection of the supraspinatus tendons revealed complete healing in all cases. No statistically significant differences were found between controls and operated-on shoulders for type I (P = .13) and type II (P = .55) muscle fibers.
  
  
  CONCLUSIONS
  Atrophy of type I and II muscle fibers in rabbit supraspinatus muscle, characterized by grade >2 fatty degeneration according to the Goutallier computed tomography classification, is reversible after 24 weeks from reattachment of its tendon. A requirement for type I and II muscle fibers hypertrophy is a change in the biomechanical and functional conditions of the muscle after its tendon is reconstructed.
authors.affiliation: Department of Arthroscopy, Minimally Invasive Surgery and Sports Traumatology, Medical University of Łódź, Łódź, Poland; FMC Private Medical Centre, Łódź, Poland. Electronic address: fabis@onet.eu.
authors.forename: Jaroslaw
authors.initials: J
authors.lastname: Fabis
authors.affiliation: Morphometry Division, Department of Pathology, Medical University of Łódź, Łódź, Poland.
authors.forename: Marian
authors.initials: M
authors.lastname: Danilewicz
authors.affiliation: Department of Arthroscopy, Minimally Invasive Surgery and Sports Traumatology, Medical University of Łódź, Łódź, Poland; FMC Private Medical Centre, Łódź, Poland.
authors.forename: Jacek T
authors.initials: JT
authors.lastname: Zwierzchowski
authors.affiliation: Clinic of Orthopaedics and Traumatology, Polish Mother's Memorial Hospital Research Institute, Łódź, Poland.
authors.forename: Kryspin
authors.initials: K
authors.lastname: Niedzielski
mesh_terms: D000273:Adipose Tissue / Q000000981:diagnostic imaging / Q000473:pathology*; D000818:Animals; D001284:Atrophy / Q000473:pathology; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000473:pathology*; D018657:Muscle Fibers, Slow-Twitch / Q000473:pathology*; D011817:Rabbits; D017006:Rotator Cuff / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D013708:Tendon Injuries / Q000473:pathology*; D014057:Tomography, X-Ray Computed; D014945:Wound Healing
keywords: Supraspinatus; fatty degeneration; muscle fibers atrophy; rabbit; sarcopenia