The pectoral girdle or shoulder girdle is the set of bones which connects the upper limb to the axial skeleton on each side. It consists of the clavicle and scapula in humans and, in those species with three bones in the pectoral girdle, the coracoid. Some mammalian species (e.g. the dog and the horse) have only the scapula.
In humans, the only joints between the shoulder girdle and axial skeleton are the sternoclavicular joints on each side. No joint exists between each scapula and the rib cage; instead the muscular connection between the two permits relatively great mobility of the shoulder girdle in relation to the pelvic girdle.
In those species having only the scapula, no joint exists between the forelimb and the thorax, the only attachment being muscular.
Joints of the Pectoral Girdle
The pectoral girdle and
pelvic girdle share many similarities, however they differ sufficiently in structure to produce markedly different functions and abilities. Because the
upper limb is not usually involved in weight bearing, its stability has been sacrificed in exchange for greater mobility.
There are three anatomical and two physiological joints in the pectoral girdle, the glenohumeral, the acromioclavicular, the sternoclavicular, the scapulocostal and the suprahumeral (or subacromial) joints respectively.
The Glenohumeral Joint
The
glenohumeral joint is the articulation between the
head of the humerus and the
glenoid cavity of the
scapula. It is a
ball and socket type of
synovial joint. The glenohumeral joint allows for
adduction,
abduction,
medial and
lateral rotation,
flexion and
extension of the arm.
The Acromioclavicular Joint
The
acromioclavicular joint is the articulation between the
acromion process of the scapula and the
lateral end of the
clavicle. It is a
plane type of synovial joint. The acromion of the scapula rotates on the acromial end of the clavicle.
The Sternoclavicular Joint
The
sternoclavicular joint is the articulation of the
manubrium of the
sternum and the
1st costal cartilage with the
medial end of the
clavicle. It is a
saddle type of synovial joint but functions as a
ball and socket joint. The sternoclavicular joint accommodates a wide range of scapula movements and can be raised to a 60° angle during
elevation of the scapula.
The Scapulocostal Joint
The
scapulocostal joint (also known as the scapulothoracic joint) is a
physiological joint formed by an articulation of the
anterior scapula and the
posterior thoracic rib cage. It is musculotendinous in nature and is formed predominantly by the
trapezius,
rhomboids and
serratus anterior muscles. The
pectoralis minor also plays a role in its movements. The gliding movements at the scapulocostal joint are
elevation,
depression,
retraction,
protraction and
superior and
inferior rotation of the scapula.
The Suprahumeral Joint
The
suprahumeral joint (also known as the subacromial joint) is a
physiological joint formed by an articulation of the
coracoacromial ligament and the
head of the humerus. It is formed by the gap between the humerus and the acromoin process of the scapula. This space is filled mostly by the
subacromial bursa and the
tendon of
supraspinatus. This joint plays a role during complex movements while the arm is fully flexed at the glenohumeral joint, such as changing a lightbulb, or painting the roof of the
Sistine Chapel.
See also
Glenohumeral joint (Shoulder joint)
Shoulder
Acromioclavicular joint
Sternoclavicular joint
External links
Category:Skeletal system
