7 Pelvic girdle

Chapter contents

Hip bone

Ilium

Ischium

Pubis

The pelvis

Measurement of pelvic size

Fractures

Hip joint

Trauma

Pathology

Sacroiliac joints

Pathology

Symphysis pubis

The pelvic girdle is formed by the 2 hip bones, the sacrum and the coccyx. For notes on the sacrum and coccyx, see Chapter 9.

Hip bone (Figs 7.1 and 7.2)

This is a large, irregularly shaped bone composed of 3 bones – the ilium, ischium and pubis – which are fused together in the adult.

Fig. 7.1 Hip bone (external aspect).

Ilium

A–Iliac crest

B–Anterior superior iliac spine

C–Inferior gluteal line

D–Anterior inferior iliac spine

E–Acetabulum

F–Greater sciatic notch

G–Posterior inferior iliac spine

H–Posterior superior iliac spine.

Pubis

1 – Superior ramus

2 – Pubic tubercle

3 – Obturator foramen

4 – Inferior ramus.

Ischium

a–Ischial ramus

b–Ischial tuberosity

c–Lesser sciatic notch

d–Ischial spine.

Fig. 7.2 Hip bone (internal aspect).

Ilium

I–Iliac crest

J–Posterior superior iliac spine

K–Auricular surface

L–Posterior inferior iliac spine

M–Greater sciatic notch

N–Iliopubic eminence

O–Medial border

P–Anterior superior iliac spine

Q–Iliac fossa.

Pubis

5 – Inferior ramus

6 – Obturator foramen

7 – Articular area for symphysis pubis

8 – Pubic tubercle

9 – Superior ramus.

Ischium

e–Ischial spine

f–Lesser sciatic notch

g–Body

h–Ischial tuberosity

i–Ischial ramus

Ilium (Figs 7.1 and 7.2)

Type

Flat bone

Position

Forms the superior aspect of the hip bone, lying mainly above the acetabulum.

Articulations

The auricular surface of the ilium with the auricular facet of the sacrum to form the sacroiliac joint.

The ilium forms part of the acetabulum, which articulates with the head of the femur to form the hip joint.

Main parts

Iliac crest –

forms the superior border, which is easily palpated and provides attachment for numerous abdominal muscles. The highest part of the crest lies at the level of the 4th lumbar vertebra.

Anterior superior iliac spine –

easily palpated and lies at the lateral end of the iliac crest.

Anterior inferior iliac spine –

a bony prominence immediately above the acetabulum.

Anterior border –

from the anterior superior iliac spine to the acetabulum.

Posterior superior iliac spine –

lies at the posterior border of the iliac crest.

Posterior inferior iliac spine –

lies approximately 2.5 cm below the posterior superior iliac spine.

Posterior border –

curved border from the posterior superior iliac spine to the posterior border of the ischium.

Greater sciatic notch –

lies below the posterior inferior iliac spine. The sciatic nerve leaves the pelvis via the notch.

Internal (medial) surface –

divided into 2 areas, the iliac fossa and the sacro-pelvic surface, which are separated by the medial border.

Iliac fossa –

concave surface for the iliacus muscle.

Sacropelvic surface –

situated between the medial and posterior borders, and divided into 3 areas:

Iliac tuberosity – upper part, roughened for ligament attachment.

Auricular surface – middle part, for articulation with the sacrum.

Pelvic surface – lower part, forms part of the wall of the true pelvis.

Medial border –

forms part of the arcuate line (the border between the ‘true’ and ‘false’ pelvis).

External (lateral) surface –

consists of a large gluteal surface superiorly and a small area inferiorly which forms part of the acetabulum.

Gluteal surface –

crossed by 3 roughened ridges for attachment of the gluteal muscles.

Iliopubic eminence –

at the junction of the ilium and the pubis. Lies at the anterior aspect of the medial border.

Ischium (Figs 7.1 and 7.2)

Type

Flat bone.

Position

Forms the posterior and inferior portion of the hip bone.

Articulations

The ischium forms part of the acetabulum, which articulates with the head of femur to form the hip joint.

Main parts

Body –

forms part of the acetabulum and the greater sciatic notch.

Ischial tuberosity –

roughened area on the posterior and inferior aspect of the body; forms attachment for the hamstrings, long head of biceps femoris and semimembranosus.

Ischial spine –

at the lower end of the greater sciatic notch, for the sacrospinous ligament.

Lesser sciatic notch –

below the ischial spine.

Ischial ramus –

thin portion of bone on the inferior aspect; is continuous with the pubic ramus.

Pubis (Figs 7.1 and 7.2)

Type

Flat bone.

Position

Forms the inferior and medial aspect of the hip bone.

Articulations

The pubis forms part of the acetabulum, which articulates with the head of the femur to form the hip joint.

The right and left pubic bones articulate with each other to form the symphysis pubis.

Main parts

Body –

forms the anterior wall of the true pelvis and articulates with the opposite pubic bone to form the symphysis pubis.

Pubic crest –

subcutaneous and forms the upper border of the body.

Pubic tubercle –

on the lateral aspect of the pubic crest, for the inguinal ligament.

Superior ramus –

forms part of the acetabulum.

Inferior ramus –

extends downwards and laterally to join the ramus of the ischium.

Obturator foramen –

large opening formed by the ischium (body and ramus) and the pubis (superior and inferior rami). The foramen is occupied by the obturator membrane.

Acetabulum (Fig. 7.3)

Cup-shaped socket on the lateral aspect of the hip bone for articulation with the head of the femur. Formed by the pubis (anterior fifth), ischium (posterior two-fifths) and ilium (superior two-fifths).

Fig. 7.3 Acetabulum.

1 – Acetabular rim

2 – Acetabular notch

3 – Acetabular fossa.

Acetabular notch –

deficiency in the inferior aspect of the acetabular rim.

Acetabular fossa –

forms the base of the acetabulum and is non-articular.

Ossification

Primary centres

Ilium –

8th week intrauterine life.

Ischium –

age 4 months.

Pubis –

age 4–5 months.

Secondary centres

Ilium –

2 centres:

iliac crest appears at puberty;

anterior inferior iliac spine appears at puberty.

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