title: Lower muscle regenerative potential in full-thickness supraspinatus tears compared to partial-thickness tears.
abstract: OBJECTIVE
  Rotator cuff tears are associated with secondary rotator cuff muscle pathology, which is definitive for the prognosis of rotator cuff repair. There is little information regarding the early histological and immunohistochemical nature of these muscle changes in humans. We analyzed muscle biopsies from patients with supraspinatus tendon tears.
  
  
  METHODS
  Supraspinatus muscle biopsies were obtained from 24 patients undergoing arthroscopic repair of partial- or full-thickness supraspinatus tendon tears. Tissue was formalin-fixed and processed for histology (for assessment of fatty infiltration and other degenerative changes) or immunohistochemistry (to identify satellite cells (CD56+), proliferating cells (Ki67+), and myofibers containing predominantly type 1 or 2 myosin heavy chain (MHC)). Myofiber diameters and the relative content of MHC1 and MHC2 were determined morphometrically.
  
  
  RESULTS
  Degenerative changes were present in both patient groups (partial and full-thickness tears). Patients with full-thickness tears had a reduced density of satellite cells, fewer proliferating cells, atrophy of MHC1+ and MHC2+ myofibers, and reduced MHC1 content.
  
  
  CONCLUSIONS
  Full-thickness tears show significantly reduced muscle proliferative capacity, myofiber atrophy, and loss of MHC1 content compared to partial-thickness supraspinatus tendon tears.
authors.affiliation: Department of Orthopaedic Surgery , Lovisenberg Diaconal Hospital, Oslo , Norway .
authors.forename: Kirsten
authors.initials: K
authors.lastname: Lundgreen
authors.forename: Oystein Bjerkestrand
authors.initials: OB
authors.lastname: Lian
authors.forename: Lars
authors.initials: L
authors.lastname: Engebretsen
authors.forename: Alex
authors.initials: A
authors.lastname: Scott
mesh_terms: D017209:Apoptosis / Q000502:physiology; D001182:Arthroscopy; D001706:Biopsy; D049109:Cell Proliferation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000473:pathology; D009124:Muscle Proteins / Q000378:metabolism; D009133:Muscular Atrophy / Q000473:pathology; D012038:Regeneration / Q000502:physiology*; D017006:Rotator Cuff / Q000473:pathology / Q000502:physiology / Q000601:surgery; D000070636:Rotator Cuff Injuries; D032496:Satellite Cells, Skeletal Muscle / Q000473:pathology; D013708:Tendon Injuries / Q000473:pathology* / Q000503:physiopathology / Q000601:surgery
chemical_list: D009124:Muscle Proteins