The Pelvic Girdle and Hip Joint 163located just below the acetabulum and the back of
the femoral neck. This ligament prevents hip internal
rotation and horizontal adduction.
Specialized Structures of the Hip
Various specialized structures and factors are asso-
ciated with the hip that provide additional joint
stability or aid with joint function. These structures
include the glenoid labrum and bursae, while suction
also makes a significant contribution.
Acetabular Labrum
In addition to the normal articular cartilage pres-
ent at the hip joint, there is a specialized ring of
fibrocartilage situated along the margin of the
acetabulum. This rim of fibrocartilage, called the
acetabular labrum (L. labrum, a lip-shaped struc-
ture), is considerably thicker at the circumference
than at the center, thus increasing the effective depth
of the acetabulum and helping to hold the femoral
head in place. In addition, by being thicker above
and behind, it helps provide cushioning for the
top and back of the acetabulum against the large
compression forces of the head of the femur during
erect stance and movements. Thus, this labrum helps
improve joint stability and protects the bone.
Suction
The hip joint has another factor facilitating joint
stability. There is a difference in atmospheric pres-
sure in the hip joint such that a vacuum is created
that pulls the head of the femur into the socket. With
the depth of the acetabulum, the presence of the
acetabular labrum, and the extensive congruency of
this joint, suction plays a more prominent role at the
hip joint. Even if all the ligaments and muscles are
cut, the joint will stay together, and relatively large
forces are required to separate the bones as long as
the capsule is intact. In adult cadavers, 45 pounds
(20 kilograms) of force was required to separate the
joint 0.1 inch (3 millimeters), and in healthy adults,
90 pounds (41 kilograms) of force was required to
separate the joint even when it was in a loose-packed
position (Smith, Weiss, and Lehmkuhl, 1996).Bursae
Numerous bursae are associated with the hip joint.
There are two that more commonly become inflamed
in dancers. One is a bursa located over the greater
trochanter as seen in figure 4.42 on page 233, which
helps protect the soft tissues that cross the back por-
tion of this projection. The other is located between
the iliopsoas and the underlying articular capsule.Muscles
In addition to the strong capsule and ligaments of
the hip, there are many strong muscles that cross the
hip joint and have a significant stabilizing effect on
the joint. Because of their importance in support-
ing the weight of the body and generating the large
forces associated with locomotor movements, these
muscles are more massive and stronger than those
associated with the upper extremity.FIGURE 4.4 Key hip joint ligaments (right hip). (A) Anterior view, (B) posterior view.