Bony pelvis

The bony pelvis is formed by the sacrum and coccyx and a pair of hip bones (os coxae or innominate bones), comprising the ischium, pubis and ilium and are part of the appendicular skeleton.

Its primary function is the transmission of forces from the axial skeleton to the lower limbs as well as supporting the pelvic viscera.

Gross anatomy

In childhood, each hip bone consists of three separate bones (ilium, ischium and pubis) connected by the triradiate cartilage. Around puberty, these bones fuse.

The two hip bones are joined anteriorly at the symphysis pubis and posteriorly to the sacrum at the sacroiliac joints. The pelvic bones incorporate the acetabulum, which articulates with the proximal femur at the hip joint.

Sex differences

Differences between the males and female bony pelvis arise as an adaptation of the female pelvis to childbearing :

  • infrapubic angle is greater than 90° in females
  • pelvic inlet shape
  • males: heart-shaped
  • females: round or oval
  • wider greater sciatic notch in females
  • acetabulum faces more anteriorly in females
  • sacrum more triangular and shorter in females
  • oval or triangular obturator foramen in females

The shape of the female bony pelvis can be described using the following terms :

  • gynaecoid pelvis (50%): normal female type
  • anthropoid pelvis (25%): long AP diameters, short transverse diameters and narrow infrapubic angle
  • android pelvis (20%): male type with conical shaped pelvic cavity and heart-shaped pelvic inlet
  • platypelloid ("flat female") pelvis (5%): short AP diameters, long transverse diameters and wide infrapubic angle
Pelvic apertures

The pelvic brim defines the pelvic inlet and the following structures contribute to it :

  • pubic crest
  • pectin pubis
  • arcuate line (of the ilium)
  • sacral ala

Pelvic outlet is formed by the following structures :

  • pubic arch
  • inferior margin of the pubic symphysis
  • pubic rami
  • ischial rami
  • sacrotuberous ligament
  • sacrum and coccyx