title: Chronic Paraspinal Muscle Injury Model in Rat.
abstract: OBJECTIVE
  The objective of this study is to establish an animal model of chronic paraspinal muscle injury in rat.
  
  
  METHODS
  Fifty four Sprague-Dawley male rats were divided into experimental group (n=30), sham (n=15), and normal group (n=9). Incision was done from T7 to L2 and paraspinal muscles were detached from spine and tied at each level. The paraspinal muscles were exposed and untied at 2 weeks after surgery. Sham operation was done by paraspinal muscles dissection at the same levels and wound closure was done without tying. Kyphotic index and thoracolumbar Cobb's angle were measured at preoperative, 2, 4, 8, and 12 weeks after the first surgery for all groups. The rats were sacrificed at 4, 8, and 12 weeks after the first surgery, and performed histological examinations.
  
  
  RESULTS
  At 4 weeks after surgery, the kyphotic index decreased, but, Cobb's angle increased significantly in the experimental group (p<0.05), and then that were maintained until the end of the experiment. However, there were no significant differences of the kyphotic index and Cobb's angle between sham and normal groups. In histological examinations, necrosis and fibrosis were observed definitely and persisted until 12 weeks after surgery. There were also presences of regenerated muscle cells which nucleus is at the center of cytoplasm, centronucleated myofibers.
  
  
  CONCLUSIONS
  Our chronic injury model of paraspinal muscles in rats shows necrosis and fibrosis in the muscles for 12 weeks after surgery, which might be useful to study the pathophysiology of the degenerative thoracolumbar kyphosis or degeneration of paraspinal muscles.
authors.affiliation: Department of Neurosurgery, Hallym University Kangnam Sacred Heart Hospital, Hallym University College of Medicine, Seoul, Korea.
authors.forename: Tack Geun
authors.initials: TG
authors.lastname: Cho
authors.affiliation: Department of Neurosurgery, Chung-Ang University Hospital, Chung-Ang University College of Medicine, Seoul, Korea.
authors.forename: Seung Won
authors.initials: SW
authors.lastname: Park
authors.affiliation: Department of Neurosurgery, Chung-Ang University Hospital, Chung-Ang University College of Medicine, Seoul, Korea.
authors.forename: Young Baeg
authors.initials: YB
authors.lastname: Kim
keywords: Animal model; Chronic injury; Degeneration; Kyphosis; Paraspinal muscle