title: Vertical pelvic ring displacement in pelvic ring injury: Measurements in pelvic outlet radiograph and in cadavers.
abstract: BACKGROUND
  Vertical pelvic ring displacement (VPRD) is a serious injury and needs assessment. Pelvic outlet radiographs are routinely taken. However, relationship of radiographic and actual VPRD is still in question. Thus, measurement of VPRD from pelvic radiographs was studied.
  
  
  METHODS
  2 dry pelvic bones and 1 sacrum from same cadaver was reconstructed to be the pelvic ring. Five specimens were enrolled. 10, 20 and 30 mm vertical displacement of right pelvic bone was performed at levels of sacroiliac joint and pubic symphysis for representing right VPRD. Then, the pelvis was set sacral inclination at 60° from X-ray table for outlet and anteroposterior pelvic radiographs. Right VPRD was measured by referring to superior most pelvic articular surface of both sacroiliac joints and sacral long axis. Radiographic VPRD and actual displacement were analyzed by Pearson correlation coefficient at more than 0.90 for the strong correlation and strongly significant simple regression analysis was set at P < 0.01.
  
  
  RESULTS
  Radiographic VPRD from outlet and anteroposterior pelvic views at 10 mm actual displacement were 20.12 ± 1.98 and 4.08 ± 3.76 mm, at 20 mm were 40.31 ± 1.97 and 9.94 ± 7.27 mm and at 30 mm were 58.56 ± 2.53 and 11.29 ± 2.89 mm. Statistical analyses showed that radiographic VPRD from pelvic outlet view is 1.95 times of actual displacement with strong correlation at 0.992 coefficient and strongly significant regression analysis (P < 0.001) with 0.984 of R (2) value. Whereas, the measurement from anteroposterior pelvic radiograph was not strongly significant.
  
  
  CONCLUSIONS
  Pelvic outlet radiograph provides efficient measurement of VPRD with 2 times of actual displacement.
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Krit
authors.initials: K
authors.lastname: Boontanapibul
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Thos
authors.initials: T
authors.lastname: Harnroongroj
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Narumol
authors.initials: N
authors.lastname: Sudjai
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Thossart
authors.initials: T
authors.lastname: Harnroongroj
keywords: Pelvic bones; Pelvic outlet radiograph; fractures; pelvic bone; radiography; sacral long axis; sacroiliac joint; vertical pelvic ring displacement