Pelvis & lower limb · Pelvis
Hip bone
The hip bone is the large bone on each side of the pelvis. The two hip bones meet each other in front at the pubic symphysis and the sacrum behind at the sacroiliac joints, forming the bony pelvis, and each carries the acetabulum, the socket of the hip joint.
- Latin (TA)
- Os coxae
- Type
- Irregular bone: it is three bones
- Side
- Paired — right and left
- Model size
- 21.5 cm longest
Showing a right bone. Rotate it to inspect every surface; switch sides to practise siding.
3D model: Z-Anatomy (CC BY-SA 4.0), derived from BodyParts3D © DBCLS (CC BY-SA 2.1 JP). Adapted by PharmaWallah. Credits & licence
Landmarks
34 of 34 marked on the modelTap a landmark to find it on the bone and read what it is.
The thick, curved upper border of the ilium, running from the anterior superior iliac spine to the posterior superior iliac spine.
Where: The whole upper margin of the ilium; palpable along its length under the skin at the waist.
Why it matters: It gives attachment to the muscles of the abdominal wall and back, and its highest point is a surface marker used for lumbar puncture level.
Related: External oblique, internal oblique, transversus abdominis, latissimus dorsi, quadratus lumborum, tensor fasciae latae.
Viva: Which muscles attach to the three parts (lips) of the iliac crest?
Marked on the model at the point Z-Anatomy places this label.
The rounded anterior end of the iliac crest.
Where: At the front of the iliac crest; easily felt at the lateral end of the groin crease.
Why it matters: Origin of sartorius and the lateral attachment of the inguinal ligament; a key landmark for measuring limb length and for orienting the bone.
Related: Sartorius (origin), inguinal ligament, tensor fasciae latae.
Viva: Which muscle arises from the anterior superior iliac spine?
Marked on the model at the point Z-Anatomy places this label.
A blunt projection on the anterior border of the ilium below the ASIS.
Where: On the anterior border of the ilium, just above the acetabulum.
Why it matters: Origin of the straight head of rectus femoris; the iliofemoral ligament is attached just below it.
Related: Rectus femoris (straight head), iliofemoral ligament.
Marked on the model at the point Z-Anatomy places this label.
The posterior end of the iliac crest.
Where: At the back of the iliac crest; it lies under the skin dimple seen above the buttock on each side.
Why it matters: A surface landmark for the sacroiliac joint region and an anchor for strong posterior sacroiliac ligaments.
Related: Posterior sacroiliac ligaments.
Marked on the model at the point Z-Anatomy places this label.
The smooth, shallow concavity on the inner (medial) surface of the ilium.
Where: The inner surface of the iliac blade, above the arcuate line.
Why it matters: Origin of iliacus, which joins psoas major to form iliopsoas, the main flexor of the hip.
Related: Iliacus (origin).
Marked on the model at the point Z-Anatomy places this label.
The outer surface of the iliac blade, marked by the gluteal lines.
Where: The lateral (outer) surface of the ilium, above the acetabulum.
Why it matters: Gives origin to the three gluteal muscles, divided between them by the gluteal lines.
Related: Gluteus maximus, medius and minimus.
Marked on the model at the point Z-Anatomy places this label.
An ear-shaped articular area on the inner surface of the ilium.
Where: On the posterior part of the medial (sacropelvic) surface of the ilium.
Why it matters: Articulates with the auricular surface of the sacrum at the sacroiliac joint.
Related: Sacroiliac joint.
Marked on the model at the point Z-Anatomy places this label.
A rounded ridge on the inner surface of the ilium.
Where: Running downwards and forwards from the auricular surface to the iliopubic eminence, below the iliac fossa.
Why it matters: Forms part of the pelvic brim (linea terminalis), which separates the greater (false) pelvis above from the lesser (true) pelvis below.
Marked on the model at the point Z-Anatomy places this label.
A large, deep notch on the posterior border of the hip bone.
Where: Between the posterior inferior iliac spine above and the ischial spine below.
Why it matters: Turned into the greater sciatic foramen by the sacrospinous and sacrotuberous ligaments; it is posterior, so it is used to orient the bone.
Viva: What converts the greater sciatic notch into a foramen?
Marked on the model at the point Z-Anatomy places this label.
A pointed projection from the posterior border of the ischium.
Where: Between the greater sciatic notch above and the lesser sciatic notch below.
Why it matters: Attachment of the sacrospinous ligament and of the superior gemellus.
Related: Sacrospinous ligament, superior gemellus, coccygeus.
Marked on the model at the point Z-Anatomy places this label.
A small, smooth notch on the posterior border of the ischium.
Where: Between the ischial spine and the ischial tuberosity.
Why it matters: Turned into the lesser sciatic foramen by the sacrospinous and sacrotuberous ligaments.
Marked on the model at the point Z-Anatomy places this label.
A large, rough mass on the lower part of the ischium.
Where: At the posteroinferior part of the hip bone, below the lesser sciatic notch.
Why it matters: Takes the body weight in sitting, and gives origin to the hamstrings and part of adductor magnus.
Related: Semitendinosus, semimembranosus, long head of biceps femoris, adductor magnus, sacrotuberous ligament, quadratus femoris.
Viva: Which muscle group arises from the ischial tuberosity?
Marked on the model at the point Z-Anatomy places this label.
The bar of bone formed by the ramus of the ischium joined to the inferior ramus of the pubis.
Where: Below and medial to the obturator foramen, forming the lower boundary of that foramen.
Why it matters: Forms the side of the pubic arch and gives attachment to the adductor muscles and the perineal membrane.
Marked on the model at the point Z-Anatomy places this label.
The flattened anterior part of the pubis.
Where: At the front of the hip bone, medial to the obturator foramen.
Why it matters: Carries the symphysial surface, pubic crest and pubic tubercle, and gives origin to adductor longus, gracilis and adductor brevis.
Marked on the model at the point Z-Anatomy places this label.
The oval, roughened medial surface of the body of the pubis.
Where: On the medial side of the body of the pubis, facing the opposite hip bone.
Why it matters: Joined to the opposite symphysial surface through the fibrocartilaginous disc of the pubic symphysis; it faces medially, so it helps side the bone.
Related: Pubic symphysis.
Marked on the model at the point Z-Anatomy places this label.
The thick upper border of the body of the pubis.
Where: On the upper edge of the body of the pubis, medial to the pubic tubercle.
Why it matters: Origin of rectus abdominis and part of the pelvic brim.
Related: Rectus abdominis, pyramidalis.
Marked on the model at the point Z-Anatomy places this label.
A small rounded projection at the lateral end of the pubic crest.
Where: At the front of the pubis, lateral to the pubic crest; palpable in the groin.
Why it matters: Medial attachment of the inguinal ligament; a landmark for telling inguinal from femoral hernias.
Related: Inguinal ligament.
Viva: Between which two points does the inguinal ligament run?
Marked on the model at the point Z-Anatomy places this label.
A sharp ridge on the upper surface of the superior pubic ramus.
Where: Running laterally from the pubic tubercle along the superior ramus to the iliopubic eminence.
Why it matters: Part of the pelvic brim, and origin of pectineus.
Related: Pectineus, lacunar and pectineal ligaments.
Marked on the model at the point Z-Anatomy places this label.
The upper bar of the pubis, passing from the body to the acetabulum.
Where: Above the obturator foramen, between the body of the pubis and the acetabulum.
Why it matters: Forms the anterior part of the acetabulum and carries the pecten pubis and obturator groove.
Marked on the model at the point Z-Anatomy places this label.
A large opening bounded by the pubis and ischium.
Where: Below and in front of the acetabulum.
Why it matters: Almost completely closed in life by the obturator membrane, which gives origin to obturator internus and externus; it lies below the acetabulum, so it helps orient the bone.
Related: Obturator membrane, obturator internus and externus.
Marked on the model at the point Z-Anatomy places this label.
The deep, cup-shaped socket on the lateral surface of the hip bone.
Where: On the outer surface, where the ilium, ischium and pubis meet.
Why it matters: Receives the head of the femur at the hip joint; it is formed by all three parts of the hip bone and is the key to siding the bone.
Related: Hip joint.
Viva: Which bones form the acetabulum?
Marked on the model at the point Z-Anatomy places this label.
The horseshoe-shaped articular part of the acetabulum, covered by hyaline cartilage.
Where: Around the margin of the acetabulum, open below at the acetabular notch.
Why it matters: The only part of the acetabulum that articulates with the femoral head.
Marked on the model at the point Z-Anatomy places this label.
The rough, non-articular floor of the acetabulum.
Where: In the centre of the acetabulum, inside the lunate surface.
Why it matters: Holds a fat pad, and the ligament of the head of the femur arises from its margins near the notch.
Marked on the model at the point Z-Anatomy places this label.
A gap in the inferior margin of the acetabulum.
Where: At the lower edge of the acetabulum, facing the obturator foramen.
Why it matters: Bridged by the transverse acetabular ligament; vessels pass beneath it to the ligament of the head of the femur. It points downwards, which helps orient the bone.
Marked on the model at the point Z-Anatomy places this label.
Classification & region
Irregular bone: it is three bones (ilium, ischium and pubis) fused into one, with a broad flat blade above and a ring of bone around the obturator foramen below, so it fits no simpler category.
- Ilium
- The broad, fan-shaped upper part. It forms the upper part of the acetabulum, carries the iliac crest, and articulates with the sacrum at the auricular surface.
- Ischium
- The posteroinferior part. Its body forms the posterior part of the acetabulum; it carries the ischial spine and the ischial tuberosity (the bone you sit on), and its ramus joins the inferior pubic ramus.
- Pubis
- The anteroinferior part. Its body meets the opposite pubis at the pubic symphysis; its superior ramus forms the anterior part of the acetabulum and its inferior ramus joins the ischial ramus.
Hold it in the anatomical position
- Find the acetabulum (the deep cup) and turn it to face outwards (laterally), and slightly forwards and downwards.
- Put the broad blade of the ilium uppermost and the obturator foramen below and in front of the acetabulum.
- Bring the pubis to the front, with its symphysial surface facing the midline, and the greater sciatic notch and ischial tuberosity to the back.
- In the anatomical position the anterior superior iliac spine and the pubic tubercle lie in the same vertical (coronal) plane, and the symphysial surface is vertical in the median plane.
Right or left? Side determination
- Identify the acetabulum: it always faces laterally, away from the midline.
- Hold the ilium up and the obturator foramen down.
- Hold it as if it were in your own pelvis: pubis (with the oval symphysial surface) pointing forwards, away from you, and the deep greater sciatic notch behind, nearest you.
- Check that the acetabular notch points downwards towards the obturator foramen.
- The acetabulum now faces the side the bone comes from: held this way, an acetabulum facing your right means a right hip bone.
Check yourself: switch the 3D model to “Left bone” and apply the same steps.
Articulations
- With the femur (head) at the Hip joint — Lunate surface of the acetabulum.
- With the sacrum at the Sacroiliac joint — Auricular surface of the ilium.
- With the opposite hip bone at the Pubic symphysis — Symphysial surface of the pubis.
Muscle and ligament attachments
| Structure | Type | Where on the bone |
|---|---|---|
| Sartorius | origin | Anterior superior iliac spine |
| Rectus femoris (straight head) | origin | Anterior inferior iliac spine |
| Rectus femoris (reflected head) | origin | Ilium just above the acetabulum (supra-acetabular groove) |
| Tensor fasciae latae | origin | Anterior part of the outer lip of the iliac crest and the ASIS |
| Gluteus maximus | origin | Gluteal surface of the ilium behind the posterior gluteal line (also from the sacrum, coccyx and sacrotuberous ligament) |
| Gluteus medius | origin | Gluteal surface between the anterior and posterior gluteal lines |
| Gluteus minimus | origin | Gluteal surface between the anterior and inferior gluteal lines |
| Iliacus | origin | Iliac fossa |
| External oblique | insertion | Anterior part of the outer lip of the iliac crest |
| Internal oblique | origin | Intermediate zone of the iliac crest (anterior part) |
| Transversus abdominis | origin | Inner lip of the iliac crest (anterior part) |
| Latissimus dorsi | origin | Posterior part of the iliac crest |
| Quadratus lumborum | origin | Posterior part of the iliac crest and iliolumbar ligament |
| Rectus abdominis | origin | Pubic crest and pubic symphysis |
| Pectineus | origin | Pecten pubis |
| Adductor longus | origin | Body of the pubis, below the pubic crest |
| Adductor brevis and gracilis | origin | Body and inferior ramus of the pubis |
| Adductor magnus | origin | Ischiopubic ramus and ischial tuberosity |
| Semitendinosus, semimembranosus and long head of biceps femoris (hamstrings) | origin | Ischial tuberosity |
| Quadratus femoris | origin | Lateral border of the ischial tuberosity |
| Superior gemellus | origin | Ischial spine |
| Inferior gemellus | origin | Upper part of the ischial tuberosity |
| Obturator internus | origin | Inner surface of the obturator membrane and the surrounding bone |
| Obturator externus | origin | Outer surface of the obturator membrane and the surrounding bone |
| Inguinal ligament | ligament | Anterior superior iliac spine to the pubic tubercle |
| Sacrospinous ligament | ligament | Ischial spine |
| Sacrotuberous ligament | ligament | Medial margin of the ischial tuberosity |
| Iliofemoral ligament | ligament | Below the anterior inferior iliac spine and the acetabular rim |
| Transverse acetabular ligament | ligament | Bridges the acetabular notch |
Functions
- Transmits body weight from the vertebral column (through the sacrum) to the femur in standing, and to the ischial tuberosities in sitting.
- Provides the socket (acetabulum) of the hip joint.
- Forms, with the sacrum and coccyx, the bony pelvis that protects the pelvic organs and, in females, forms the birth canal.
- Gives attachment to the muscles of the trunk, gluteal region and thigh.
Clinical & practical relevance
- The iliac crest is a common site for bone marrow aspiration and for taking bone grafts, because it is subcutaneous and easy to reach.
- A line joining the highest points of the iliac crests crosses the lumbar spine and is used to find the level for lumbar puncture.
- Pelvic ring fractures can tear pelvic vessels and organs and cause severe internal bleeding.
- Avulsion fractures can occur in young athletes where strong muscles pull on an apophysis, for example at the ASIS (sartorius), AIIS (rectus femoris) or ischial tuberosity (hamstrings).
- The pubic tubercle is used to tell an inguinal hernia (above and medial to it) from a femoral hernia (below and lateral to it).
Identification tips
- The acetabulum always faces outwards: once it faces laterally, the ilium is up and the pubis points forwards, the side reads off at once.
- Think of the posterior border from top to bottom: PSIS, PIIS, greater sciatic notch, ischial spine, lesser sciatic notch, ischial tuberosity.
- The ASIS and pubic tubercle sit in the same vertical plane in the anatomical position, which means the pelvis is tilted forwards.
- Remember 'gluteal lines from back to front: maximus, medius, minimus' — each muscle is further forward and smaller.
Common student mistakes
- Calling the obturator foramen the acetabulum, or holding the bone with the obturator foramen above the acetabulum.
- Thinking the whole acetabulum is articular: only the lunate surface is.
- Confusing the greater and lesser sciatic notches with the foramina: the notches are bone; the foramina are completed by the sacrospinous and sacrotuberous ligaments.
- Placing the pubic symphysis surface laterally: it faces the midline.
Common exam questions
Name the three parts of the hip bone and say where they meet.Show answer
Ilium, ischium and pubis; they meet and fuse at the acetabulum.
How do you determine the side of a hip bone?Show answer
Acetabulum facing laterally, ilium up, obturator foramen below, pubis in front and greater sciatic notch behind; the acetabulum then faces the side the bone belongs to.
What forms the pelvic brim?Show answer
The sacral promontory and ala of the sacrum, the arcuate line of the ilium, the pecten pubis, the pubic crest and the upper margin of the pubic symphysis.
Name the parts of the acetabulum and say which one is articular.Show answer
The horseshoe-shaped lunate surface is articular; the acetabular fossa and acetabular notch are non-articular.
What passes through the greater and lesser sciatic foramina?Show answer
Piriformis, the sciatic nerve, the gluteal vessels and nerves and the pudendal nerve leave through the greater; the obturator internus tendon and the pudendal nerve and internal pudendal vessels pass through the lesser.
Give the attachments of the gluteal muscles on the ilium.Show answer
Gluteus maximus behind the posterior gluteal line, medius between the anterior and posterior lines, and minimus between the anterior and inferior lines.
Which muscles arise from the ischial tuberosity?Show answer
The hamstrings (semitendinosus, semimembranosus and long head of biceps femoris), part of adductor magnus, quadratus femoris and the inferior gemellus.
What closes the obturator foramen, and what passes through the obturator canal?Show answer
The obturator membrane; the obturator nerve and vessels pass through the canal at its upper edge.
Revision summary
- Three fused parts: ilium, ischium, pubis, meeting at the acetabulum.
- Acetabulum faces laterally; obturator foramen below it; pubis anterior; greater sciatic notch posterior.
- Iliac crest runs from ASIS to PSIS; inguinal ligament runs from ASIS to pubic tubercle.
- Ischial spine separates the greater and lesser sciatic notches; sacrospinous and sacrotuberous ligaments turn them into foramina.
- Ischial tuberosity: hamstrings, and weight in sitting.
- Articulates with the femur (hip), sacrum (sacroiliac) and the opposite hip bone (pubic symphysis).
Test yourself on the hip bone
Spotting questions on bones, sides and landmarks — untimed, with explanations.
Joints of the hip bone
References
- Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. 5th ed. Philadelphia: Elsevier; 2023.
- Moore KL, Dalley AF, Agur AMR. Moore's Clinically Oriented Anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2023.
- Federative International Programme for Anatomical Terminology (FIPAT). Terminologia Anatomica. 2nd ed. FIPAT.library.dal.ca; 2019. fipat.library.dal.ca/TA2
- Kervyn G, Zielinski M, Vinent L, et al. Z-Anatomy: the libre 3D atlas of anatomy. Models derived from BodyParts3D, The Database Center for Life Science (CC BY-SA 2.1 JP). CC BY-SA 4.0. www.z-anatomy.com/
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