Hip bone (Os coxae) is a large paired bone that forms the side and front of the pelvis, the bony framework at the base of the trunk. It lies between the sacrum behind and the thigh bone below, supporting body weight and forming the socket of the hip joint.
Where is the hip bone located?
The left hip bone and right hip bone lie on opposite sides of the lower trunk. Together with the sacrum, the wedge-shaped bone at the base of the vertebral column, they form the pelvic ring. At the front, the hip bones meet in the midline.
Each hip bone lies beside the pelvic cavity, the space containing structures such as the urinary bladder and rectum. Its outer surface faces the buttock and hip region, while its inner surface faces towards the pelvic contents. Below and laterally, meaning away from the midline, it meets the femur, the thigh bone.
As part of the skeletal system, the body's supporting framework of bones, the hip bone links the trunk with the lower limb. Its broad upper region also forms part of the greater pelvis, which supports the lower abdominal contents.
What are the parts of the hip bone?
The hip bone develops from the ilium, ischium and pubis. These unite around the acetabulum, the cup-shaped socket that receives the head of the femur. In the adult, they form one continuous bone, although their regions remain anatomically distinguishable.
| Part | Location | Main features |
|---|---|---|
| Ilium | Broad upper part | Iliac crest, iliac fossa and the surface that joins the sacrum |
| Ischium | Lower and posterior part | Ischial spine and ischial tuberosity |
| Pubis | Lower and anterior part | Pubic body and rami, which extend towards the acetabulum and ischium |
The ilium spreads upwards as a broad wing. The ischium forms the lower region towards the back, and the pubis extends towards the front midline. A ramus is a branch-like portion of bone; the pubic and ischial rami help surround the large opening below the acetabulum.
What are the main surfaces and landmarks?
The iliac crest is the curved upper border of the ilium. Its anterior end forms the anterior superior iliac spine, a prominent point at the front of the hip. The posterior superior iliac spine marks its end towards the back; additional spines lie below these upper projections.
On the inner surface, the iliac fossa is a broad concavity occupied by the iliacus muscle, which helps bend the hip. Behind it, the auricular surface is an ear-shaped area that joins the sacrum. The outer surface of the ilium bears gluteal lines, ridges associated with attachments of the buttock muscles.
Other important landmarks include:
- Ischial tuberosity: a rough prominence that bears weight during sitting and gives attachment to several muscles, including most of the hamstrings at the back of the thigh.
- Ischial spine: a pointed projection above the tuberosity that provides attachment for muscles and ligaments, bands of connective tissue that stabilise joints or connect bones.
- Obturator foramen: the large opening bounded by the pubis and ischium. A connective-tissue sheet called the obturator membrane closes most of it, leaving a passage for the obturator nerve and vessels.
- Greater and lesser sciatic notches: indentations along the posterior border. Ligaments complete them into openings through which structures pass between the pelvis and neighbouring regions.
Which joints does the hip bone form?
The hip bone contributes to the articular system, the body's joints, through connections that combine stability with movement. It joins the sacrum, the opposite hip bone and the femur.
The sacroiliac joint connects the auricular surface of the ilium with the sacrum. Strong surrounding ligaments stabilise this connection, which transfers weight from the vertebral column towards the lower limbs and permits limited movement.
The pubic symphysis joins the pubic bodies at the front of the pelvis through a disc of fibrocartilage, a tough supporting tissue. The hip joint is a ball-and-socket joint between the acetabulum and the femoral head. A cartilage rim called the acetabular labrum deepens the socket.
What does the hip bone do?
The hip bone transfers weight between the trunk and lower limb during standing and movement. During sitting, the ischial tuberosities provide major points of support. Together, the hip bones and sacrum also surround and help protect the pelvic contents.
For the muscular system, the hip bone provides attachment sites for muscles that move the hip, support the pelvic floor and act on the trunk. The pelvic floor is the muscular support beneath the pelvic organs. The acetabulum allows the femoral head to move within a stable socket, supporting bending, straightening and rotation at the hip.
How can you tell a left hip bone from a right one?
Orient the bone with the iliac crest upwards and the acetabulum facing outwards. The pubis should point forwards and towards the midline, while the ischial tuberosity lies below and behind the socket.
The iliac fossa faces inwards towards the pelvic cavity. Checking these features together is more reliable than using a single projection to determine the side.
How can you locate the hip bone in the 3D model?
In the 3D model beside this article, select a hip bone and isolate it, then rotate and zoom to change your view. You can also hide other selected structures or fade them rather than isolating your selection.
Switch layers to change the view, and use rotation and zoom to adjust the viewing angle and scale. You can cut a section along the sagittal, coronal or transverse plane, or pull parts apart. These controls offer different ways to arrange your view while keeping the selected hip bone as your focus.