376 Dance Anatomy and Kinesiology
join onto the sternum and cartilage of the first rib
(first costal cartilage) to form the sternoclavicular
joint (figure 7.4B). The sternoclavicular joint can
be classified as a saddle joint (Moore and Agur,
1995), and it contains a fibrocartilage articular disc
that divides the joint cavity into two and serves as a
shock absorber. This small joint serves as the only
bony attachment of the entire upper extremity to the
axial skeleton. However, the sternoclavicular joint is
surrounded by a fibrous capsule that is reinforced by
various strong ligaments, and it is a stable joint that
is rarely dislocated.
Laterally, the paired clavicles join with the acro-
mion processes of their respective scapulae at the
acromioclavicular joints (figure 7.4A). This gliding
joint (Moore and Agur, 1995) is surrounded by a
capsule and reinforced by various strong ligaments.
These ligaments limit the range of motion possible
at this joint and prevent the clavicle and acromion
process from being pulled apart (Kreighbaum and
Barthels, 1996). However, they are not very effective
at preventing the clavicle from riding over the top
of the acromion when a lateral blow is applied to
the shoulder, and two nearby strong ligaments (thetrapezoid and conoid coracoclavicular ligaments)
further connect the clavicle to the scapula via the
coracoid process and provide indirect support to
help prevent such a dislocation.
Functionally, movements of the sternoclavicular
joint, and to a lesser degree the acromioclavicular
joint, contribute to movements of the shoulder girdle.
It is less complex to describe the combined movements
of these joints in terms of the resultant movements of
the scapulae that they create. These movements of the
scapulae on the thorax are sometimes referred to as
occurring at the scapulothoracic “joints,” although
these are not true joints. Possible movement pairs
of the scapulae include scapular elevation-depres-
sion, abduction-adduction, and upward rotation-
downward rotation (figure 7.5) (Smith, Weiss, and
Lehmkuhl, 1996).
With elevation, the scapula as a whole moves
upward toward the ear. This movement occurs
when the shoulders are shrugged, such as in jazz
isolations. Depression is the opposite movement
to elevation and involves movement of the scapula
as a whole downward. During standing, gravity will
tend to depress the scapulae when the elevators ofFIGURE 7.3 Bony landmarks of the right humerus. (A) Anterior view, (B) posterior view.