Page 142 - Clinical Anatomy

ECA2 7/18/06 6:43 PM Page 127

The bony and ligamentous pelvis 127

tuberosities when sitting. (The sacroiliac joint is reinforced for this task as
will be described below.)
3◊◊During walking the pelvis swings from side to side by a rotatory move-
ment at the lumbosacral articulation which occurs together with similar
movements of the lumbar intervertebral joints. Even if the hip joints are
fixed, this swing of the pelvis enables the patient to walk reasonably well.
4◊◊As with all but a few small bones in the hand and foot, the pelvis pro-
vides attachments for muscles.
5◊◊In the female it provides bony support for the birth canal.

Joints and ligamentous connections of
the pelvis

The symphysis pubis is the name given to the cartilaginous joint between the
pubic bones. Each pubic bone is covered by a layer of hyaline cartilage and
is connected across the midline by a dense layer of fibrocartilage. The centre
of the latter may break down to form a cleft-like joint space which, however,
is not seen before the first decade and which is not lined by a synovial
membrane.
The joint is surrounded and strengthened by fibrous ligaments, espe-
cially above and below.
The sacroiliac joints are the articulations between the auricular surfaces
of the sacrum and ilium on each side and are true synovium-lined and
cartilage-covered joints.
The sacrum ‘hangs’ from these joints supported by the extremely dense
posterior sacroiliac ligaments lying posteriorly to the auricular joint surfaces.
These support the whole weight of the body, tending to drag the sacrum
forward into the pelvis and, not surprisingly, are the strongest ligaments in
the body.
Their action is assisted by an interlocking of the grooves between the
auricular surfaces of the sacrum and ilium.
The sacrotuberous ligament passes from the ischial tuberosity to the side
of the sacrum and coccyx.
The sacrospinous ligament passes from the ischial spine to the side of the
sacrum and coccyx.
These two ligaments help to define two important exits from the pelvis:
1◊◊the greater sciatic foramen—formed by the sacrospinous ligament and the
greater sciatic notch;
2◊◊the lesser sciatic foramen—formed by the sacrotuberous ligament and the
lesser sciatic notch.

Note.◊There is a useful surface landmark in this region, the dimple con-
stantly seen on each side immediately above the buttock, which defines:
1◊◊the posterior superior iliac spine;
2◊◊the centre of the sacroiliac joint;
3◊◊the level of the second sacral segment;
4◊◊the level of the end of the dural canal of the spinal meninges.