Pelvis Anatomy

The bony pelvis is a ring-shaped structure formed by the two hip bones (each a fused ilium, ischium, and pubis), the sacrum, and the coccyx. It links the vertebral column to the lower limbs, transmits the weight of the upper body to the legs, supports and protects the pelvic organs, and—in females—forms the bony birth canal.

Definition

The bony pelvis is the ring of bone formed by the paired hip bones (os coxae) together with the sacrum and coccyx, joined at the sacroiliac joints and pubic symphysis, which connects the axial skeleton to the lower limbs and transmits body weight.

Scope

This topic covers the bones forming the pelvic ring (hip bones, sacrum, coccyx), the joints that close the ring (sacroiliac joints and pubic symphysis), the division into greater (false) and lesser (true) pelvis, and characteristic anatomical sex differences. It is a reference-educational account of normal structure, not clinical guidance.

Core questions

• Which bones form the pelvic ring and how do they fuse?
• What joints close the pelvic ring and how do they transfer load?
• How is the pelvis divided into the greater and lesser pelvis?
• What are the principal anatomical differences between the male and female pelvis?

Key concepts

• Hip bone (ilium, ischium, pubis) and acetabulum
• Sacrum and coccyx
• Sacroiliac joints and pubic symphysis
• Pelvic ring and load transfer
• Greater (false) and lesser (true) pelvis
• Pelvic inlet and outlet
• Sex differences in pelvic shape

Mechanisms

The pelvis is a closed bony ring: each hip bone (formed by fusion of the ilium, ischium, and pubis at the acetabulum) articulates posteriorly with the sacrum at a sacroiliac joint and meets its partner anteriorly at the pubic symphysis. Body weight passing down the vertebral column is transferred through the sacrum and sacroiliac joints to the hip bones and then to the lower limbs; the sacroiliac joint is a heavily ligament-reinforced articulation specialized for stable load transfer with limited movement (Vleeming et al., 2012). Because it is a ring, disruption at one point of the pelvis is commonly accompanied by injury elsewhere in the ring, and the closely related vascular anatomy is relevant to the management of pelvic trauma (Hak et al., 2004). The female pelvis is generally adapted for childbirth, with a wider, more rounded inlet, while the male pelvis tends to be narrower and deeper.

Clinical relevance

Pelvic anatomy underpins the interpretation of pelvic imaging, the description of pelvic-ring and acetabular fractures, and the understanding of the bony birth canal in obstetrics. The content here characterizes normal structure and general injury patterns for orientation and learning, and is not a basis for diagnosing or treating any individual.

History

Descriptive osteology of the pelvis and its sex differences is a long-standing part of anatomy preserved in standard references (Standring, 2020), while the integrated biomechanical understanding of the sacroiliac joint and the pelvic ring in load transfer and trauma is more recent (Vleeming et al., 2012; Hak et al., 2004).

Seminal works

• vleeming-2012
• standring-2020

Frequently asked questions

Which bones make up the bony pelvis?

The bony pelvis is formed by the two hip bones (each created by fusion of the ilium, ischium, and pubis) together with the sacrum and the coccyx, joined at the two sacroiliac joints behind and the pubic symphysis in front.

What is the difference between the greater (false) and lesser (true) pelvis?

The greater (false) pelvis lies above the pelvic inlet and is bounded by the flaring iliac wings, supporting abdominal contents, whereas the lesser (true) pelvis lies below the inlet, contains the pelvic organs, and forms the bony birth canal.