Anatomy · Bones

Hip bone

Also the coxal bone, os coxae or innominate bone

Pelvic girdle · pelvis

The hip bone is the large, curved, irregular bone that forms the side and front of the pelvis. It is made of three bones, the ilium, ischium and pubis, which fuse in the late teens and meet in the deep cup of the acetabulum. It joins the sacrum behind at the sacroiliac joint and its fellow in front at the pubic symphysis, and it receives the head of the femur to form the hip joint.

How to spot them

▸Large twisted, fan-shaped bone: a broad flaring upper blade (ilium) and a ring-like lower part enclosing a big opening
▸A deep cup on its outer surface, the acetabulum, where the three parts meet
▸A large oval opening below and in front of the acetabulum, the obturator foramen, between ischium and pubis
▸Curved upper border (iliac crest) that can be felt with the hands on the hips

What to know

A large, curved bone made of three fused parts that come together in a deep cup on its outer face

Hip bone — ilium, ischium and pubis meeting in the acetabulum.

The one bone of the body that allows the most accurate determination of sex

Hip bone — the female pelvis is adapted for childbirth.

Once known as the 'bone without a name' because its three parts each have a different name

Hip bone — the innominate bone (os innominatum).

In a child, a Y-shaped cartilage in its cup keeps its three parts separate until the late teens

Hip bone — the triradiate cartilage.

Its large oval opening below the socket is nearly closed by a membrane, and a nerve and vessels pass through a notch in it

Hip bone — the obturator foramen and obturator membrane.

Each is joined behind to the sacrum at a strong, almost immobile joint, and in front to its opposite number at a cartilaginous joint

Hip bone — the sacroiliac joint and the pubic symphysis.

The cup on its outer face has a horseshoe-shaped articular surface around a central non-articular floor, and receives the ball of the thigh bone

Hip bone — the acetabulum, with its lunate surface and acetabular fossa.

Key ideas

The pelvic girdle is a single hip bone on each side; unlike the pectoral girdle, it is strongly united to the axial skeleton and to its fellow, for stability and weight-bearing.
The acetabulum is formed by ilium (about two fifths), ischium (two fifths) and pubis (one fifth).

Quick-fire facts

•Each adult hip bone is formed by the fusion of the ilium, ischium and pubis, which fuse in the late teens; before that they are separated by Y-shaped triradiate cartilage in the acetabulum.
•The word coxal comes from Latin coxa, hip; os coxae, coxal bone and innominate bone are all synonyms.
•The greater sciatic notch is narrower and deeper in males and broader in females.
•The ischial tuberosity bears the weight when we sit; the iliac crest and anterior superior iliac spine are landmarks palpable in front.
•It is the single bone that allows the most accurate determination of sex from the skeleton (OpenStax).
•The obturator foramen is commonly described as the largest foramen in the skeleton; it is closed by the obturator membrane.
•The acetabulum's horseshoe-shaped articular surface is the lunate surface; its floor is the acetabular fossa.
•The two hip bones, the sacrum and the coccyx together form the bony pelvis.

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Sources

OpenStax — Anatomy and Physiology 2e — 8.3 The Pelvic Girdle and Pelvis
TeachMeAnatomy — Hip Bone — Bones of the Pelvis