The Pelvic Girdle and Hip Joint 159bone that is the largest of the three bones. It forms
the upper and side “winged” portion of the pelvis. Its
internal surface, which is large, smooth, and concave,
is termed the iliac fossa (L. fossa, a trench or ditch)
as seen in figure 4.1C. The superior convex border
of the ilium is termed the iliac crest (L. crista, bony
ridge) and can be easily palpated below the waist
on the sides of the body, running both forward and
backward. The top of the iliac crest is generally level
with the space between the spines of the fourth and
fifth lumbar vertebrae (L4-L5). If the crests are fol-
lowed in an anterior direction, they begin to curve
downward, and the bony prominences that can be
felt on the front of the pelvis are called the anterior
superior iliac spines (L. spina, short, sharp process of
bone). If the crests are followed in a posterior direc-
tion, a rough, broader prominence can be felt—the
posterior superior iliac spines as seen in figure 4.1A.
These landmarks are often abbreviated the ASIS and
PSIS, respectively, and are key for evaluating pelvic
symmetry and alignment.
The ischium is an irregular bone that is the stron-
gest of the three bones. It is located in the lower,
posterior portion of the pelvis. The most inferior
portion of this bone has roughened eminences, upon
which we sit, that are termed the ischial tuberosities
(L. tuber, a knob) (figure 4.1B) or “sitz bones.” You
can easily palpate the tuberosities of the ischium
while sitting on a chair by leaning forward and plac-
ing the fingers under the bottom of the pelvis from
behind. Then, slowly begin to rock your weight back
to sit upright, and the tuberosities can be felt press-
ing down on the fingers. You can also palpate them
in a standing position by placing the fingertips at the
bottom of the buttocks and slowly leaning the trunk
slightly backward and forward. This landmark is key
for teaching turnout and pelvic alignment. The ischial
tuberosities lie in approximately the same horizontal
plane as the lesser trochanters of the femurs.
A thin, flattened portion of the ischium, called the
ramus (L. a branch), ascends upward and forward to
join with the inferior ramus of the pubis as seen in
figure 4.1B. The pubis is also an irregular bone, and
it is located in the anterior and inferior portion of the
pelvis. The thin and flattened superior ramus of the
pubis ascends to join with the ilium. These rami, as well
as other portions of the pubis and ischium, form a large
opening in the pelvis termed the obturator foramen
(L. foramen, an aperture). This is the largest foramen
in the body. The obturator (L. obturo, to occlude an
opening) foramen is covered by a membrane, and this
membrane and the surrounding bones form attach-
ments for muscles that are key for effecting turnout in
dance (the deep outward rotator muscles).
Each os coxae also contains a horseshoe-shaped
cavity, composed of elements of the ilium, ischium,
and pubis, called the acetabulum (L. a shallow vessel
or cup), which can be seen in figure 4.1B. Its lower
margin is incomplete, and the gap is called the
acetabular notch. The spherical proximal end of
the femur, called the head of the femur (L. femur,
thigh) and seen in figure 4.2, fits into this hip socket
or acetabulum. Distal to the head, the femur tapers
to form the neck of the femur, which is a common
fracture site in older women. This neck angles to join
with the long shaft of the femur. At this junction,
two large bony projections are located. The largest
projection faces laterally and is appropriately termed
the greater trochanter (L. major bony prominence).
The smaller projection, located on the medial aspect
of the upper femur, is termed the lesser trochanter
(L. minor bony prominence). The line running
between these projections on the front of the femur
is termed the intertrochanteric line (L. line between
trochanters), while the prominent ridge located
on the back of the shaft of the femur is termed the
linea aspera (L. linea, line + asper, rough), as seen in
figure 4.2B.
You can locate the greater trochanter of the femur
by placing your thumb on the lateral aspect of the
crest of the ilium and reaching down on the thigh
with the middle finger. When you internally and
externally rotate the leg, you should feel the greater
trochanter move beneath the skin. This landmark
is useful for evaluating hip mechanics and body
alignment. During standing, the tip of the greater
trochanter is approximately level with the center of
the head of the femur.
When studying the bones that make up the pelvis,
it is interesting to note that this is one area of the
skeleton where there are marked gender-linked differ-
ences necessary to meet the demands of childbearing.
The female pelvis is generally broader, roomier, and
less vertical than that of a male and has a wider inlet
(superior pelvic aperture) and larger outlet (inferior
pelvic aperture). The coccyx and sacrum are also situ-
ated more posteriorly in women than in men (Mercier,
1995; Moore and Dalley, 1999). In contrast, the pelvis
of the male is narrower and deeper.Joint Structure and Movements of the Pelvic Girdle
The os coxae are firmly joined to the sacrum posteri-
orly at the sacroiliac joints and anteriorly to each other
at the pubic symphysis to form one solid structure, the
pelvic girdle. The pelvic girdle provides a link between