The geometry of bony pelvis differs significantly between males and females – the phenomena caused by adaptation to the obstetric demands. Females have a relatively larger and rounder pelvic cavity, a shorter and more posteriorly projecting sacrum, a wider subpubic angle, and smaller acetabula with a larger distance between them1,2. It is, however, worth mentioning that in real-life, the gender dimorphism of the pelvis is not as evident as generally described3,4.
The images presented here demonstrates the classically dimorphic pelvises with the length dimensions based on multiple sources of evidence5–10. The range of reference values reflects rather "average," than "the normal" range, or, by use of statistical terms — rather 95% Confidence Interval, than the double Standard Deviation.
Front view of the male and female pelvis.
Note the gender difference in distance between two spina iliaca anterior superior (anterior spinal distance), the size of the acetabular fossa and the subpubic angle. The terminal line is a border between the greater and lesser pelvis.
The list of terms:Pelvis major – Greater pelvis Pelvis minor – Lesser pelvis Linea terminalis – Terminal line Arcus pubis – Pubic arch Angulus subpubicus – Subpubic angle Crista iliaca – Iliac crest Distantia intercristalis – Intercristal distance Spina iliaca anterior superior – Anterior superior iliac spine
Anterior spinal distance (iliac bi-spinous diameter)
Top aspect of the male and female pelvis.
Note the pelvic inlet (apertura pelvis superior) — the upper opening of the lesser pelvis is bordered by the terminal line. The term conjugate apply to the pelvimetric distances in the median plane. The subtypes of conjugates are reviewed below.
The list of terms:Apertura pelvis superior – Upper opening of lesser pelvis (pelvic inlet) Promontorium – Promontory of sacrum Ala ossis sacri – Ala sacralis Articulatio sacroiliaca – Sacroiliac joint Linea arcuata – Arcuate line Eminentia iliopubica – Iliopubic (iliopectineal) eminence Pecten ossis pubis – Pecten (pectineal line) of the pubis Symphisis pubica – Pubic symphysis Diameter conjugata – Conjugate diameter Diameter transversa – Subpubic angle Diameter obliqua – Oblique diameter
Bottom view of the male and female pelvis.
The list of terms:Apertura pelvis inferior – Lower pelvic aperture (pelvic outlet) Coccyx Lig. sacrotuberale – Sacrotuberal ligament Tuber ischiadicum – Ischial tuberosity Arcus pubicus – Pubic arch Distantia interspinosa – Interspinous distance Diameter transversum – Transverse diameter of the pelvic outlet Conjugata recta – Straight conjugate
Medial view to the female pelvis. The left hip bone is removed to demonstrate the main pelvimetric conjugates used in obstetrics.
Note that anatomical straight conjugate is not particularly relevant. The sacrococcygeal joint is relatively elastic, adding some mobility to the coccygeal bone, so coccyx usually dislocates dorsally during childbirth*.
The list of terms:Axis pelvis – Pelvic axis Conjugata anatotmica – Anatomic conjugate Conjugata vera (gynecologica) – Obstetrical conjugate Conjugata diagonalis – Diagonal conjugate
Sagittal outlet diameter Conjugata recta – Straight conjugate Inclinatio pelvis – Pelvic inclination
360° rotation of the male pelvis.
First published: Apr/2020
Last update: 12/Aug/2021