(1) The ilium is divided into a body and a flared portion called the ala, or
wing. The upper border of the ala is called the iliac crest. This crest terminates
anteriorly as the anterior superior iliac spine (ASIS), below which is situated the anterior
inferior iliac spine (AIIS). The crest of the ilium terminates posteriorly as the posterior
superior iliac spine (PSIS), below which is situated the posterior inferior iliac spine
(PIIS). The greater sciatic notch is situated below the posterior inferior iliac spine
(figure 2-16). The internal or medial surface of the ilium presents a large, smooth,
concave depression called the iliac fossa. Behind the iliac fossa is a rough surface
divided into two portions. The superior portion is the iliac tuberosity and the inferior
portion is the auricular surface. A curved line, the arcuate line, that marks the inferior
boundary of the major or false pelvis indicates the inferior boundary of the iliac fossa.
The obturator foramen is a large aperture situated between the ischium and the pubis
and inferior to the acetabulum.
(2) The ischium is composed of a body, a superior ramus, and an inferior
ramus. The ischial spine or sciatic spine projects posteriorly from the body. Situated
below the spine is the lesser sciatic notch. The superior ramus branches downward
from the body. The ischial tuberosity is situated on the posterior aspect of the superior
ramus. The inferior ramus extends from the lower part of the superior ramus to join the
inferior ramus of the pubis.
(3) The pubis is divided into a body (which forms part of the acetabulum), a
superior ramus, and an inferior ramus. The superior ramus projects anteromedially
from the pubic body. The lateral portion of the superior ramus is marked by a rough
iliopectineal eminence that indicates the fusion of the ilium and the pubis. The medial
portion presents a pubic tubercle, which projects ventrally. The symphysial surface is
the articulating surface by means of which the left pubis and right pubis are joined.
2-14. ARTICULATIONS OF THE LOWER EXTREMITY
a. Sacroiliac. The union of the auricular surfaces of the sacrum and the ilium
forms the sacroiliac joint. It is a slightly movable joint.
b. Symphysis Pubis. The junction of the symphysial surfaces of the pubic
bones forms the symphysis pubis. The pubic fibrocartilaginous lamina is interposed
between the symphysial surfaces. This is a slightly movable joint.
c. Hip. The hip is formed by the head of the femur articulating with the
acetabulum of the os coxa. It is a ball-and-socket joint. The movements permitted by
the hip include flexion (swinging forward), extension, abduction, adduction, rotation, and