title: Comparison of two methods for measuring the pubococcygeal line from sagittal-plane magnetic resonance imaging.
abstract: OBJECTIVE
  The pubococcygeal line (PCL) is an important reference line for determining measures of pelvic organ support on sagittal-plane magnetic resonance imaging (MRI); however, there is no consensus on where to place the posterior point of the PCL. As coccyx movement produced during pelvic floor muscle (PFM) contractions may affect other measures, optimal placement of the posterior point is important. This study compared two methods for measuring the PCL, with different posterior points, on T2-weighted sagittal MRI to determine the effect of coccygeal movement on measures of pelvic organ support in older women.
  
  
  METHODS
  MRI of the pelvis was performed in the midsagittal plane, at rest and during PFM contractions, on 47 community-dwelling women 60 and over. The first PCL was measured to the tip of the coccyx (PCLtip) and the second to the sacrococcygeal joint (PCLjnt). Four measures of pelvic organ support were made using each PCL as the reference line: urethrovesical junction height, uterovaginal junction height, M-line and levator plate angle.
  
  
  RESULTS
  During the PFM contraction the PCLtip shortened and lifted (P < 0.001); the PCLjnt did not change (P > 0.05). The changes in the four measures of pelvic organ support were smaller when measured relative to the PCLtip as compared to those to the PCLjnt (P < 0.001).
  
  
  CONCLUSIONS
  Coccyx movement affected the length and position of the PCLtip, which resulted in underestimates of the pelvic-organ lift produced by the PFM contraction. Therefore, we recommend that the PCL be measured to the sacrococcygeal joint and not to the tip of the coccyx.
authors: Centre de Recherche de l'institut Universitaire do Gériatrie de Montréal, Montréal, Québec, Canada.
authors: Stéphanie
authors: S
authors: Madill
authors: An
authors: A
authors: Tang
authors: Stéphanie
authors: S
authors: Pontbriand-Drolet
authors: Chantal
authors: C
authors: Dumoulin
mesh_terms: D000368:Aged; D059925:Anatomic Landmarks; D003050:Coccyx / Q000033:anatomy & histology* / Q000502:physiology; D005260:Female; D006801:Humans; D007596:Joints / Q000033:anatomy & histology* / Q000502:physiology; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009068:Movement; D009119:Muscle Contraction; D015588:Observer Variation; D017773:Pelvic Floor / Q000033:anatomy & histology* / Q000502:physiology; D011792:Quebec; D015203:Reproducibility of Results; D012447:Sacrum / Q000033:anatomy & histology* / Q000502:physiology; D014521:Urethra / Q000033:anatomy & histology; D014599:Uterus / Q000033:anatomy & histology; D014621:Vagina / Q000033:anatomy & histology