The pelvis is made up of four bones segments. The sacrum is a plate of bone at the base of the spine with the coccyx attached to the lower end of the sacrum. The two large bones that make up the front and sides of the pelvis are constructed from the Ilium (upper section), Ischium (the bone of your bottom) and Pubic bones (the relatively thin section at the front) which are fused together. These two plates are joint posteriorly to the sacrum by the sacro-iliac joint – often referred to as the SIJ – and anteriorly by a cartilage section called the symphysis pubis.
The pelvis is therefore a complete circle of bone and structurally very strong, designed to withstand the high forces put through it by all our movements.
The male and female pelvis differs in shape due to the need for the female to cope with birth. The angle between the Ilium and Ischium is steeper in females so the sides of the pelvis are more vertical creating a larger diameter internally.