title: Extraordinary muscular structure leads to urethral injury after vaginal delivery in animal study.
abstract: OBJECTIVE
  The aim of this study is to explore causality of birth trauma after vaginal delivery and anatomical findings.
  
  
  METHODS
  A total of 28 virgin mice were studied. Treatment groups received vaginal distention. Specimens were collected and subjected to the following fluorescence stains: progenitor cell (c-kit), smooth muscle (SMA), fibroblast (vimentin), and skeleton muscle (Masson's trichrome). Confocal microscopy was used to screen all of the urogenital tissue to localize the stained cells.
  
  
  RESULTS
  Fibroblasts were spread all over perivaginal and urethral surroundings. Progenitor cells appeared at urethral-vagina intersection and urethral circle. They were noticeable only within smooth muscle layer. Two extraordinary skeleton muscle bands appeared on the urethra bilaterally.
  
  
  CONCLUSIONS
  Our study demonstrates existence of muscle bands at the bilateral urethra. They can limit the mobility of urethra during vaginal delivery and thereby cause urethra injury. Progenitor cells are located only in the smooth muscle of the urethral circle.
authors.affiliation: Medical School, Chang Gung University, Tao-Yuan, Taiwan, Republic of China. chin671009@gmail.com
authors.forename: Hung-Yen
authors.initials: HY
authors.lastname: Chin
authors.forename: Eileen
authors.initials: E
authors.lastname: Changchien
authors.forename: Chi-Hsin
authors.initials: CH
authors.lastname: Chiang
authors.forename: Hsiu-Ping
authors.initials: HP
authors.lastname: Yang
mesh_terms: D000818:Animals; D036861:Delivery, Obstetric / Q000009:adverse effects*; D005260:Female; D051379:Mice; D008810:Mice, Inbred C57BL; D009130:Muscle, Smooth / Q000473:pathology; D014521:Urethra / Q000293:injuries* / Q000473:pathology; D014550:Urinary Incontinence, Stress / Q000209:etiology*