Biology of the Shoulder

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Glenohumeral Joint

 

Function:

The glenohumeral joint is a ball-and-socket joint that allows for the arm to move in a circular rotation as well as movement of the arm towards and away from the body. The motion that the glenohumeral joint provides is flexion, extension, abduction and adduction. For images of these movements, see http://www.exrx.net/Articulations/Shoulder.html#anchor105322 (1).

 

Bones:

The glenohumeral joint is a ball-and socket joint that is formed between two bones, the humerus and the scapula. The humerus head, acting as the ball, fits into the end of the scapula known as the glenoid, the socket. In this specific joint, the humerus head, however, does not fit perfectly within the glenoid because the humerus head is much larger than the surface area of the glenoid socket. This size discrepancy creates a situation where the two bones do not snugly fit together without the help of other physical structures. Thus this joint is dependent upon other structures for stability (2).

Cartilage:

The most important piece of cartilage is the labrum, otherwise descibed as the articular cartilage. The labrum is a piece of cartilage that lies directly between the the humerus head and the glenoid. This piece of cartilage provides a smooth surface that allows for the humerus head to rotate with minimal friction, thus cushioning both the humerus and the scapula. Also, the labrum is shaped like a ring, with the outer part of the labrum being much thicker than the center of the ring. This specific shape allows for the labrum to fit against the humerus head and the glenoid, physically matching up the larger humerus head with the small surface of the glenoid. Thus the labrum is also very important for the stabilization of the joint (3).

http://www.athleticadvisor.com/Injuries/UE/Shoulder/shoulder.htm
 

Muscles:

Rotator Cuff

The main muscles that are used in conjunction with the glenohumeral joint are the group of muscles known as the rotator cuff. The rotator cuff is made up of four muscles, the supraspinatus, subscapularis, infraspinatus, and teres minor. All four of these muscles connect the scapula to the humerus. One main purpose of the rotator cuff muscles is to pull the humerus into the scapula such that the two bones are fitted tightly against one another. Thus rotator cuff muscles are important for stabilizing the glenohumeral joint. Strengthening of the rotator cuff helps prevent further instability and repeat damage after the shoulder has dislocated. The other important role of the rotator cuff is to help with movement of the arm, particularly the rotation of the arm. The supraspinatus helps with abduction of the arm, and is particularly susceptible to injury during flexion and abduction of the arm (4).

 
http://www.medicalmultimediagroup.com/pated/shoulder_problems/cufftearold.html

 

Ligaments:

In addition to the labrum and the rotator cuff muscles, other structures exist that help with the stabilization and movement of the joint. There are four ligaments that help with the glenohumeral joint. These ligaments are the coracohumeral ligament (between the coracoid process and the humerus) and the three glenohumeral ligaments (between the glenoid and the humerus) (5).

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Created by: Blair Smith, Connie Lee, Daniel Solomon, Matthew Whitson and Stephanie Chang
Date last modified: 5/2/2004