378 Dance Anatomy and Kinesiology
the scapulae stop contracting. However, when the
body weight is supported on the hands with the
arms down by the sides, the scapular depressors
must be contracted to hold the scapulae down to
prevent undesired elevation and to stabilize the
scapulae so the trunk can be elevated. Abduction or
protraction of the scapulae involves movement of
the scapulae away from the spinal column and each
other, sometimes referred to in dance as “widening
the shoulder blades.” Adduction or retraction of
the scapulae is the opposite motion to abduction,
and it involves bringing the scapulae toward each
other and toward the spinal column; in dance this
is sometimes referred to as “pinching the shoulder
blades.” Upward rotation of the scapula involves
turning the scapula about an axis through the spine
of the scapula such that the glenoid cavity moves
upward while the inferior angle moves laterally and
anteriorly on the thorax. This motion is hard to
produce in isolation but is an essential movement
that accompanies overhead movements of the arm.
The opposite motion, downward rotation, involves
a downward rotation of the glenoid cavity. It can be
exaggerated through bringing the hand behind the
low back. Some authors also include tilts, not further
described in this text.
Note that these movements do not have an exact
counterpart in the lower extremity because the bones
of the pelvis cannot move independently. However,
the movements of the pelvic girdle as a whole relative
to the spine at the lumbosacral joint serve a similar
function of adjusting the relationship of the pelvis
so that movements of the femur are fostered. How-
ever, one important difference is that due to the
relatively rigid linking of the pelvis posteriorly with
the sacrum (at the sacroiliac joints), movement of
one side of the pelvis will have a direct effect on
the opposite side. In contrast, due to the fact that
the scapulae are only linked muscularly posteriorly,
movement of one scapula and arm can occur inde-
pendently with minimal effect on the position or
function of the opposite arm.Joint Structure and Movements of the Shoulder
While the movements of the scapula just described
position the scapula to help facilitate movements of
the arm, the movement of the arm actually occurs at
the joint formed between the glenoid cavity of the
scapula and the head of the humerus. This joint is
called the shoulder joint or glenohumeral joint (see
figure 7.4A). The glenohumeral joint is a triaxial,ball-and-socket joint. Both the head of the humerus
and glenoid cavity are covered with articular cartilage.
This glenoid cavity is quite shallow, and only about
one-fourth to one-third of the almost hemispherical
head of the humerus makes contact with the glenoid
cavity (Frankel and Nordin, 1980). Furthermore,
the shape of the glenoid cavity is less curved and
more elongated (pear shaped) while the head of the
humerus is more spherical (Caillet, 1996), so that
rather than simple rotation occurring about a fixed
axis, the axis of rotation shifts as the shoulder joint
moves and the humeral head moves linearly (trans-
lates) as well as rotates (Hall, 1999). So, the shoulder
joint represents a very complex and much less stable
ball-and-socket joint that is more prone to dislocation
and recurrent subluxation than the hip joint.
As with other ball-and-socket joints, the shoulder
joint has three degrees of motion: flexion-extension
approximately in the sagittal plane (figure 7.6A),
abduction-adduction approximately in the frontal
plane, and external-internal rotation approximately
in the transverse plane (figure 7.6B). The special-
ized terms of horizontal abduction and horizontal
adduction (figure 7.6C) are given to movements of
the arm occurring in a horizontal plane with the arm
at shoulder height. Also, as with the hip joint, many
movements that occur during dance do not occur in
exact anatomical planes. Some texts give a specialized
term, scaption, to one of these types of movement.
Because the glenoid cavity faces slightly anterior to
the frontal plane, some authors hold that a more
natural movement is abduction in the plane of the
scapula, or scaption, rather than pure abduction in
the frontal plane. Another unique term used at the
shoulder joint is elevation. The term elevation is
generally used to describe movement of the humerus
away from the side in any plane. Note that this is a
movement of the arm, in contrast to the “elevation”
used to describe movement of the scapula. Many
of the movements at the glenohumeral joint can
occur through a very large range of motion, and the
shoulder joint is the most freely movable joint in the
human body (Hall, 1999).Shoulder Joint Capsule and Key Ligaments
The shoulder joint is surrounded by a sleevelike
fibrous capsule lined with synovial membrane that is
attached proximally to the perimeter of the glenoid
cavity. Distally it is attached to the anatomical neck
of the humerus, except medially, where it is attached
slightly lower on the humerus. The capsule is loose;
for example, when the arm is down by the side,
there are hanging folds in the inferior portion of