Bony Anatomy of the Shoulder Girdle
Scapula, Humerus, Clavicle, and the Joints of the Shoulder
Jun 5, 2009
The shoulder girdle is a collection of bones and joints involving the upper arm, scapula, clavicle and sternum.
The Shoulder Joints
The true shoulder joint, or glenohumeral joint, is made up of the head of the humerus (the upper arm bone) nestling against the scapula (shoulder blade) in its glenoid fossa, a shallow depression at the outer top corner of the scapula.
The scapula is joined to the clavicle at the acromioclavicular or AC joint, where the acromion process of the scapula meets the clavicle just superior to the glenoid fossa.
The clavicle is anchored to the manubrium of the sternum at the sternoclavicular joint, the only point at which the shoulder girdle has a bony anchor to the torso.
There is another pseudo-joint sometimes called the scapulothoracic joint where the scapula slides over the ribs.
Anatomy of the Scapula
The scapula itself is a flattish bone shaped a little like Africa. On the left scapula, the glenoid fossa is near Morocco. The coast across the top is called the superior border of the scapula. Down its right-hand side is called the medial or vertebral border. The southernmost point, around the Cape of Good Hope, is called the inferior angle. The west coast is called the lateral border.
Toward the top of the scapula, from Mauritania in the west to the Sudan in the east, is a pronounced ridge like a huge mountain range called the scapular spine; above it, the scapula drops away to form a continent-wide valley called the supraspinous fossa, and below it, the rest of the scapula is flattened out into the infraspinous fossa.
The scapula also has two sides: the superficial side, exposed to the sky, and the deep side, or the underground surface that sits against the ribcage. The entire deep surface forms another shallow depression called the subscapular fossa.
At the westernmost edge, the spine of the scapula goes up and forms a roof over the glenoid fossa called the acromion process. Additionally, there is a hooked knob on the deep surface of the scapula, extending deep into the earth below Mali, called the coracoid process; it goes through to the front of the body and can be felt as a knobbly point just below the collarbone.
Of course, these directions are mirrored in the right scapula.
Anatomy of the Humerus
The humerus, or upper arm bone, is a long bone with a classic knob at each end. At the superior end, which forms the shoulder, is the humeral head. It has two distinct swellings called the lesser and greater tuberosities, which are separated by a groove called the bicipital groove or intertubercular sulcus.
Anatomy of the Clavicle
The clavicle is a long bone with a subtle S-shaped curvature. At its lateral edge, it meets the acromion process of the scapula; at its medial edge, it articulates with the sternum.
An awareness of the several different joints that exist between the scapula, humerus, clavicle, sternum, and ribcage makes it easier to appreciate the function and structure of the shoulder girdle.
See also: Anatomy of the Rotator Cuff
 |
