title: Magnetic resonance imaging and histologic evidence of postoperative back muscle injury in rats.
abstract: METHODS
  Postoperative back muscle injury was evaluated in rats by magnetic resonance imaging and histologic analyses.
  
  
  OBJECTIVE
  To compare the magnetic resonance imaging manifestation of back muscle injury with the histologic findings in rats and to subsequently clarify the histopathologic appearance of the high intensity regions on T2-weighted images in human postoperative back muscles.
  
  
  BACKGROUND
  In a previous study, it was found that the signal intensity on T2-weighted images of the postoperative back muscles was increased in patients who had postsurgical lumbar muscle impairment, especially in those with a prolonged surgery duration. However, the specific histopathologic changes that cause the high signal intensity on T2-weighted images remain unclear.
  
  
  METHODS
  Rats were divided into three groups: sham operation group, 1-hour retraction group, and 2-hour retraction group. Magnetic resonance imaging and histology of the multifidus muscles were examined before surgery and at 2, 7, and 21 days after surgery.
  
  
  RESULTS
  T2-weighted imaging was more useful than T1-weighted imaging to estimate back muscle injury. The high signal intensity of the multifidus muscles on T2-weighted images remained 21 days after surgery only in the 2-hour retraction group. Histologically, the regeneration of the multifidus muscles was complete at 21 days after surgery in the 1-hour retraction group, but the regenerated muscle fibers in the 2-hour retraction group had a small diameter, and the extracellular fluid space remained large.
  
  
  CONCLUSIONS
  The high signal intensity on T2-weighted images of the postoperative multifidus muscles in the regenerative phase may be due to an increased extracellular space and incomplete muscle fiber regeneration.
authors.affiliation: Departments of Orthopaedic Surgery and Physiology, Faculty of Medicine, Toyama Medical and Pharmaceutical University, Toyama, Japan. g6410101@ms.toyama-mpu.ac.jp
authors.forename: R
authors.initials: R
authors.lastname: Gejo
authors.forename: Y
authors.initials: Y
authors.lastname: Kawaguchi
authors.forename: T
authors.initials: T
authors.lastname: Kondoh
authors.forename: E
authors.initials: E
authors.lastname: Tabuchi
authors.forename: H
authors.initials: H
authors.lastname: Matsui
authors.forename: K
authors.initials: K
authors.lastname: Torii
authors.forename: T
authors.initials: T
authors.lastname: Ono
authors.forename: T
authors.initials: T
authors.lastname: Kimura
mesh_terms: D000818:Animals; D005110:Extracellular Space; D008161:Lumbosacral Region / Q000473:pathology / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000473:pathology; D018482:Muscle, Skeletal / Q000293:injuries* / Q000473:pathology*; D019637:Orthopedic Procedures; D011183:Postoperative Complications / Q000175:diagnosis*; D051381:Rats; D017208:Rats, Wistar; D014945:Wound Healing