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Pelvic diameters

Asked by Anonymous

  • Antero -posterior diameters:
    • Anatomical antero-posterior diameter (true conjugate) = 11cm
      • from the tip of the sacral promontory to the upper border of the symphysis pubis.
    • Obstetric conjugate = 10.5 cm
      • from the tip of the sacral promontory to the most bulging point on the back of symphysis pubis which is about 1 cm below its upper border. It is the shortest antero-posterior diameter.
    • Diagonal conjugate = 12.5 cm
      • i.e. 1.5 cm longer than the true conjugate. From the tip of sacral promontory to the lower border of symphysis pubis.
    • External conjugate = 20 cm
      • from the depression below the last lumbar spine to the upper anterior margin of the symphysis pubis measured from outside by the pelvimeter . It has not a true obstetric importance.
  • Transverse diameters:
    • Anatomical transverse diameter =13cm
      •  between the farthest two points on the iliopectineal lines.
      •  It lies 4 cm anterior to the promontory and 7 cm behind the symphysis.
      •  It is the largest diameter in the pelvis.
    • Obstetric transverse diameter:
      • It bisects the true conjugate and is slightly shorter than the anatomical transverse diameter.
  • (C) Oblique diameters:
    •  Right oblique diameter =12 cm
      • from the right sacroiliac joint to the left iliopectineal eminence.
    •  Left oblique diameter = 12 cm
      • from the left sacroiliac joint to the right iliopectineal eminence.
    •  Sacro-cotyloid diameters = 9-9.5 cm
      • from the promontory of the sacrum to the right and left iliopectineal eminence, so the right diameter ends at the right eminence and vice versa.


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