Pelvic girdle

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7 Pelvic girdle

Chapter contents

Measurement of pelvic size

Sacroiliac joints

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.

Ilium (Figs 7.1 and 7.2)

Type

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.

Pubis (Figs 7.1 and 7.2)

Type

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

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.

The pelvis (Figs 7.4 and 7.5)

The pelvis is formed posteriorly by the sacrum and coccyx and anteriorly by the two hip bones.

Fig. 7.4 Female pelvis (anterior aspect).

A–Iliac crest

B–Iliac fossa

C–Sacral promontory

D–Arcuate line

E–Ischial spine

G–Obturator foramen

H–Symphysis pubis

K–Pelvic brim

M–Anterior superior iliac spine

N–Sacroiliac joint.

Fig. 7.5 Male pelvis (anterior aspect).

B–Arcuate line

C–Ischial tuberosity

E–Symphysis pubis.

The greater (false) pelvis

The upper portion of the pelvis is referred to as the greater pelvis. It is larger than the lesser (true) pelvis and lies above the pelvic brim; the pelvic brim is the oblique plane formed by the sacral promontory posteriorly, the arcuate line of the ilium and the pecten pubis (iliopectineal line) laterally and the pubic tubercle and crest and the upper border of the symphysis pubis anteriorly. The greater pelvis forms part of the abdominal cavity.

The lesser (true) pelvis

The lesser pelvis lies below the pelvic brim and can be divided into 3 areas:

The pelvic inlet

Bounded by the pelvic brim.

Male – heart-shaped.

Female – circular.

The pelvic outlet

Formed by the pubic arch – the rami of the ischium and pubis anteriorly the sacrotuberous ligaments and the ischial tuberosities laterally and the apex of the sacrum posteriorly.

The pelvic cavity

The area between the inlet and the outlet contains the rectum, bladder and parts of the reproductive system.

Table 7.1 Differences between the male and female pelvis

	Male	Female
General shape	Narrow, deep	Wide, shallow
Bone structure	Heavy	Light
Pelvic cavity	Long, tapering downwards	Short, cylindrical
Sacrum	Narrow, long, curved	Wide, short, less curved
Pelvic inlet	Heart-shaped	Circular
Ischial tuberosities	Close	Wide apart
Pubic arch	Less than 90°	More than 90°
Greater sciatic notch	Acute, narrow	90°, wide
Symphysis pubis	Limited movement	More flexible

Measurement of pelvic size (Figs 7.8 and 7.9)

It is sometimes necessary to establish that the pelvis is of a suitable size to permit the normal passage of a fetus.

Fig. 7.8 Pelvic measurements (anterior aspect).

A–Transverse diameter

B–Interspinous diameter.

Fig. 7.9 Pelvic measurements (lateral aspect).

C–True conjugate diameter

D–Anteroposterior diameter.

Measurement of the pelvic inlet

True conjugate diameter –

the anteroposterior measurement from the upper, inner border of the symphysis pubis to the sacral promontory in the midline.

Transverse diameter –

the maximum distance across the pubic inlet.

Measurement of the pelvic outlet

Anteroposterior diameter –

between the lower, inner border of the symphysis pubis and the apex of the sacrum.

Intertuberous diameter –

between the ischial tuberosities.

Hip joint (Figs 7.10 and 7.11)

Fig. 7.10 Left hip joint (coronal section).

B–Articular hyaline cartilage

C–Synovial membrane

D–Ligament of head of femur

E–Transverse acetabular ligament

F–Synovial fluid

G–Head of femur

H–Fibrous capsule

I–Articular hyaline cartilage

J–Synovial fluid

K–Acetabular labrum.

Fig. 7.11 Left hip joint (anterior aspect).

1 – lliofemoral ligament

2 – Pubofemoral ligament.

Type

Synovial ball and socket joint.

Bony articular surfaces

The head of the femur with the acetabulum of the hip bone. The articular surfaces are covered with articular hyaline cartilage, except for the fovea of the head of femur.

Fibrous capsule

Attached medially to the edge of the acetabulum, the acetabular labrum and the transverse acetabular ligament, anteriorly to the intertrochanteric line and laterally to the neck of femur. The capsule is loose inferiorly to allow movement.

Synovial membrane

Lines the fibrous capsule and covers the ligament of the head of femur, the intracapsular part of the neck of femur and the pad of fat in the acetabular fossa. The membrane secretes synovial fluid, which lubricates the joint.

Intracapsular structures

Acetabular labrum –

fibrocartilaginous rim round the acetabulum to deepen the socket.

Pad of fat –

lies in the acetabular fossa.

Movements

Flexion by the iliacus and the psoas assisted by the rectus femoris.

Extension by the gluteus maximus, assisted by the hamstrings.

Abduction by the gluteus medius and the gluteus minimus.

Adduction by the adductor muscles.

Medial rotation by the anterior parts of the gluteus medius, the gluteus minimus and the tensor fasciae latae.

Lateral rotation by the obturator, gemelli and quadriceps femoris.

Circumduction by a combination of the above movements.

Blood supply

Branches of the obturator, gluteal and femoral arteries.

Nerve supply

Branches of the femoral, obturator and gluteal nerves.

Radiographic appearances of the hip joint (Figs 7.12, 7.13 and 7.14)

Fig. 7.13 Hip joint: lateral projection.

1 – Ischial spine

2 – Acetabulum

3 – Ischial tuberosity

4 – Greater trochanter

5 – Lesser trochanter

6 – Shaft of femur

7 – Greater trochanter

8 – Neck of femur

9 – Head of femur

10 – Iliac crest

11 – Pubic ramus

12 – Symphysis pubis.

(From Bryan 1996.)

Fig. 7.14 Right hip joint: CT scan.

A–Greater trochanter

C–Head of femur.

(From Bryan 1996.)

Slipped upper femoral epiphysis

Epiphysis is displaced backwards and downwards.

Radiological sign –

imperfect alignment of the epiphysis with the neck of femur.

Perthes’ disease (Fig. 7.17)

Osteochondritis of the epiphysis of the femoral head.

Fig. 7.17 Perthes’ disease, right femoral head.

(Courtesy of Ernest Higginbottom.)

Radiological signs –

widening of the epiphyseal line, irregular metaphyseal outline, flattened epiphysis. Some increase in bone density within the head of femur.

Sacroiliac joints

Type

Synovial plane joint.

Bony articular surfaces

The articular surface of the ilium with the auricular facet of the sacrum; the joint spaces are directed obliquely forwards. The articular surface on the ilium is covered with articular hyaline cartilage and that on the sacrum with fibrocartilage.

Fibrous capsule

Attached medially to the sacrum and laterally to the ilium.

Synovial membrane

Lines the fibrous capsule. Secretes synovial fluid, which lubricates the joint.

Related

Bones and Joints A Guide for Students