380 Dance Anatomy and Kinesiology
head of the biceps brachii. The glenoid labrum has
been found to be vital for joint stability, as well as
increasing the surface area of contact of the head of
the humerus (Levine and Flatlow, 2000) and serving
to add a cushioning effect against the impact associ-
ated with forceful movements of the arms.Bursae
There are various bursae located about the shoulder
joint. Two bursae that lie deep to the deltoid muscle
and separate and cushion the muscles of the rotator
cuff from the overlying coracoacromial arch and
sometimes become inflamed are the subdeltoid and
subcoracoid bursae. These bursae are located close
to each other, are sometimes connected, and hence
are often jointly referred to as the subacromial bursa
(see figure 7.7B)(Mercier, 1995).Muscles
Limited stability is provided by the glenoid labrum
and bony articulation, and the glenohumeral liga-
ments and capsule primarily provide restraints at the
extremes of motion; hence, the muscles surround-
ing the joint are essential for providing stabilization(particularly in midrange shoulder motion), as well
as movement (Park, Blaine, and Levine, 2002). This
stabilization role can be demonstrated by the fact
that when these shoulder muscles are paralyzed, the
shoulder joint will tend to sublux, with the weight of
the hanging arm separating the head of the humerus
from the glenoid cavity. This observation has led to the
expression that the shoulder is a “muscle-dependent
joint.” Hence adequate strength, balanced strength,
and coordinated activation of the muscles of this
region are essential for optimal function and injury
prevention.Description and Functions of Individual Muscles of the Shoulder Complex
There are many ways in which the muscles of the
shoulder complex can be organized and described.
This text will use a functional approach, dividing the
muscles into three groups—the scapular muscles, the
rotator cuff, and other major glenohumeral muscles.
(See Individual Muscles of the Shoulder Complex,
pp. 381-394.)FIGURE 7.7 The shoulder joint (right shoulder). (A) Anterior view, (B) lateral view with head of the humerus removed.