Joints of the Shoulder Complex

MEDICAL UNIVERSITY OF SOUTH CAROLINA
COLLEGE OF HEALTH PROFESSIONS
REHABILITATION SCIENCES DEPARTMENT

The Joints of the Shoulder Complex

Four joints are defined. All 4 must be functional to permit maximum use of the upper limb.

Glenohumeral joint - most familiar of the 4 joints. Consists of the articulation between the glenoid cavity of the scapula and head of the humerus (Netter: 398). The glenohumeral joint has the greatest freedom of movement of any joint, but is also the most frequently dislocated joint (generally in an anterior/interior direction). Due to its large humeral head, its small glenoid cavity, and its loose capsule, the glenohumeral joint is designed to produce movement around an infinite number of axes intersecting in the humeral head. Such movements can be broken down into basic components as follows, along transverse, sagittal, and coronal planes, respectively:

rotation: may be demonstrated best by locking the elbow in flexion, holding the arm close to the trunk, and moving the hand and forearm out away from the trunk and back again (170 degrees total rotation, with external rotation contributing 80 degrees and internal rotation contributing 90 degrees).

flexion/extension: may be demonstrated by moving the arm with the elbow extended up (flexion) and down (extension) in an anteroposterior direction. Approximately 90-100 degrees of flexion can occur with the scapula stabilized; with full upward rotation of the scapula, flexion may be measured at 170-180 degrees (the last few degrees may be due to trunk bending). Flexion is most easily accomplished with the glenohumeral joint in an internally rotated position (Blakely and Palmer, 1984).

abduction/adduction: may be demonstrated by moving the arm with the elbow extended back and forth in a straight line which lies immediately anterior to the trunk. Assuming the glenohumeral joint to be externally rotated, abduction may be accomplished actively to 120 degrees with the scapula stabilized; if the scapula is allowed to concurrently upwardly rotate, then full abduction may be measured at 170-180 degrees (as in flexion, the last few degrees of abduction may be due to trunk bending). The concurrent upward rotation of the scapula in an approximate 1:2 ratio with humeral elevation during abduction is referred to as the "scapulohumeral rhythm". Adduction of the glenohumeral joint generally courses 0-25 degrees, and is accompanied by downward rotation of the scapula.

1. Joint classification - Ball and socket (synovial joint).

2. Ligaments - structures supporting the head of the humerus in the glenoid cavity. The ball and socket arrangement does not fit well, but is deepened by a rim of fibrocartilage around the edge of the glenoid cavity called the glenoid labrum.

a. Coracohumeral ligament: supports the head of the humerus in the glenoid cavity as a rope and assists the glenohumeral ligaments in reinforcing the anterior portion of the glenohumeral joint. Note the coracohumeral ligament as it attaches to the coracoid process and the greater tuberosity of the humerus (Netter: 398).

b. Articular (joint) capsule - thick, tough, yet pliable membrane which surrounds the joint (Netter: 398). Note that there are 2 openings in the joint capsule: 1) at the upper end of the intertubercular groove, which allows the passage of the tendon of the long head of the biceps brachii from the capsule into the groove (note the transverse humeral ligament as it stretches between the greater and lesser tuberosities and arches over the tendon as it emerges from the capsule - the transverse humeral ligament keeps the tendon positioned in the groove during shoulder movement); and, 2) an opening which serves as a communication anteriorly between the joint cavity and the subscapular bursa.

c. Glenohumeral ligaments (3) thickenings of the joint capsule protecting the glenohumeral joint anteriorly. They are identified via their attachments as (Netter: 398):
1. Superior:glenoid labrum -> fossa above the lesser tuberosity.
2. Middle:glenoid labrum -> lesser tuberosity.
3. Inferior:glenoid labrum -> anatomic neck of the humerus.

Sternoclavicular joint - articulation between the clavicle and manubrium of the sternum. The SC joint is the only point of bony connection between the trunk and upper limb (Netter: 171, 395). Movements of the SC joint consist of elevation (30-45 degrees maximum, which occurs with scapular elevation) and depression (5-10 degrees maximum - limited by the first rib - which occurs with scapular depression). Other movements include retraction/protraction (15 degrees each), and rotation (40 degrees total). Rotation occurs as the arm is elevated to allow the acromial end of the clavicle to rise in concert with the scapula (Brunnstrom, 1996).

1. Joint classification: has movements but not the form of a ball and socket joint. Located within the cavity of the SC joint is an articular disk (fibrocartilage) which provides a cushion for movement.

2. The SC joint's supporting ligaments allow the joint to be well anchored.
1. Anterior/Posterior sternoclavicular ligaments (thickenings of the joint capsule) (Netter: 395)
2. Costoclavicular ligament (1st rib -> clavicle) (Netter: 171, 395)
3. Interclavicular ligament (lies in the supraclavicular notch) (Netter: 171, 395)

Acromioclavicular (AC) joint - point at which the clavicle articulates laterally with the acromion (Netter: 396, 397). Little movement occurs at this joint, with the movements being reflected in scapular elevation, abduction (protraction), and rotation. These movements (8 degrees in any direction, as measured by Neer and Rockwood, 1984) serve to give flexibility to the distal shoulder girdle so that the glenoid fossa may face upward, downward, or forward, as the need be, to allow functional movement of the upper limb.

1. Joint classification: Plane (gliding) joint with an articular disk.

2. Supporting ligaments (Netter: 398):
a. Acromioclavicular ligament: forms the superior capsule of the AC joint. The capsule then continues around the AC joint itself with the formation of 2 small anterior and posterior AC ligaments.
b. Coracoclavicular ligament: consists of the conoid ligament (medial) and the trapezoid ligament (lateral), which bind the scapula to the clavicle. When the head of the clavicle rotates forward at the SC joint, the lateral clavicle elevates (because of the "S" shape, which tenses the coracoclavicular ligament and, in turn, helps elevate the scapula; thus shoulder girdle elevation occurs).

Scapulothoracic joint (Netter: 170): not a true joint (sometimes referred to as a "false" or "pseudo" joint) and is formed by the scapula as it glides over the posterior thorax. Movements include: elevation (approximately 60 degrees- 80 degrees measured at the acromion process); depression (approximately 5-10 degrees); protraction (abduction)/retraction (adduction) (approximately 30 degrees total movement- as measured at the SC joint). A circular movement may also be produced by combining all these movements. The scapula is connected to the clavicle via the coracoclavicular ligament, and thus, moves in conjunction with the clavicle. The scapulothoracic joint is primarily supported by the serratus anterior (Netter: 177, 178). Loss of the serratus anterior (i.e. long thoracic nerve injury) produces "scapular winging".

Coracoacromial ligament: The coracoacromial ligament is stretched between the coracoid process and the acromion and completes, with the acromion and clavicle, a bony-ligamentous arch which covers the head of the humerus. The coracoacromial ligament is triangular in shape, with its base arising from the coracoid process. It is relatedabove to the clavicle and deltoid; below to the subacromial bursa and the tendon of the supraspinatus. Along with the bony structures, the coracoacromial ligament creates a passageway for the exit of the supraspinatus (supraspinatus outlet), as it leaves its scapular origin to insert on the greater tuberosity of the humerus. Via its attachments, the coracoacromial ligament further stabilizes and anchors the acromion; irritation of the subacromial bursa by this ligament can also produce subacromial bursitis.

Click to see the images below:

Glenohumeral joint

Sternoclavicular joint

Scapulothoracic joint

Coracoacromial ligament and Acromioclavicular joint

Rotator Cuff - Chest Muscles -Fascia -Bursae- Shoulder Index

Last modified:5:09 PM on 12/1/96

Four joints are defined. All 4 must be functional to permit maximum use of the upper limb.
Glenohumeral joint - most familiar of the 4 joints. Consists of the articulation between the glenoid cavity of the scapula and head of the humerus (Netter: 398). The glenohumeral joint has the greatest freedom of movement of any joint, but is also the most frequently dislocated joint (generally in an anterior/interior direction). Due to its large humeral head, its small glenoid cavity, and its loose capsule, the glenohumeral joint is designed to produce movement around an infinite number of axes intersecting in the humeral head. Such movements can be broken down into basic components as follows, along transverse, sagittal, and coronal planes, respectively:
	rotation: may be demonstrated best by locking the elbow in flexion, holding the arm close to the trunk, and moving the hand and forearm out away from the trunk and back again (170 degrees total rotation, with external rotation contributing 80 degrees and internal rotation contributing 90 degrees).
	flexion/extension: may be demonstrated by moving the arm with the elbow extended up (flexion) and down (extension) in an anteroposterior direction. Approximately 90-100 degrees of flexion can occur with the scapula stabilized; with full upward rotation of the scapula, flexion may be measured at 170-180 degrees (the last few degrees may be due to trunk bending). Flexion is most easily accomplished with the glenohumeral joint in an internally rotated position (Blakely and Palmer, 1984).
	abduction/adduction: may be demonstrated by moving the arm with the elbow extended back and forth in a straight line which lies immediately anterior to the trunk. Assuming the glenohumeral joint to be externally rotated, abduction may be accomplished actively to 120 degrees with the scapula stabilized; if the scapula is allowed to concurrently upwardly rotate, then full abduction may be measured at 170-180 degrees (as in flexion, the last few degrees of abduction may be due to trunk bending). The concurrent upward rotation of the scapula in an approximate 1:2 ratio with humeral elevation during abduction is referred to as the "scapulohumeral rhythm". Adduction of the glenohumeral joint generally courses 0-25 degrees, and is accompanied by downward rotation of the scapula.
1. Joint classification - Ball and socket (synovial joint).
2. Ligaments - structures supporting the head of the humerus in the glenoid cavity. The ball and socket arrangement does not fit well, but is deepened by a rim of fibrocartilage around the edge of the glenoid cavity called the glenoid labrum.
	a. Coracohumeral ligament: supports the head of the humerus in the glenoid cavity as a rope and assists the glenohumeral ligaments in reinforcing the anterior portion of the glenohumeral joint. Note the coracohumeral ligament as it attaches to the coracoid process and the greater tuberosity of the humerus (Netter: 398).
	b. Articular (joint) capsule - thick, tough, yet pliable membrane which surrounds the joint (Netter: 398). Note that there are 2 openings in the joint capsule: 1) at the upper end of the intertubercular groove, which allows the passage of the tendon of the long head of the biceps brachii from the capsule into the groove (note the transverse humeral ligament as it stretches between the greater and lesser tuberosities and arches over the tendon as it emerges from the capsule - the transverse humeral ligament keeps the tendon positioned in the groove during shoulder movement); and, 2) an opening which serves as a communication anteriorly between the joint cavity and the subscapular bursa.
	c. Glenohumeral ligaments (3) thickenings of the joint capsule protecting the glenohumeral joint anteriorly. They are identified via their attachments as (Netter: 398): 1. Superior:glenoid labrum -> fossa above the lesser tuberosity. 2. Middle:glenoid labrum -> lesser tuberosity. 3. Inferior:glenoid labrum -> anatomic neck of the humerus.
Sternoclavicular joint - articulation between the clavicle and manubrium of the sternum. The SC joint is the only point of bony connection between the trunk and upper limb (Netter: 171, 395). Movements of the SC joint consist of elevation (30-45 degrees maximum, which occurs with scapular elevation) and depression (5-10 degrees maximum - limited by the first rib - which occurs with scapular depression). Other movements include retraction/protraction (15 degrees each), and rotation (40 degrees total). Rotation occurs as the arm is elevated to allow the acromial end of the clavicle to rise in concert with the scapula (Brunnstrom, 1996).
	1. Joint classification: has movements but not the form of a ball and socket joint. Located within the cavity of the SC joint is an articular disk (fibrocartilage) which provides a cushion for movement.
	2. The SC joint's supporting ligaments allow the joint to be well anchored. 1. Anterior/Posterior sternoclavicular ligaments (thickenings of the joint capsule) (Netter: 395) 2. Costoclavicular ligament (1st rib -> clavicle) (Netter: 171, 395) 3. Interclavicular ligament (lies in the supraclavicular notch) (Netter: 171, 395)
Acromioclavicular (AC) joint - point at which the clavicle articulates laterally with the acromion (Netter: 396, 397). Little movement occurs at this joint, with the movements being reflected in scapular elevation, abduction (protraction), and rotation. These movements (8 degrees in any direction, as measured by Neer and Rockwood, 1984) serve to give flexibility to the distal shoulder girdle so that the glenoid fossa may face upward, downward, or forward, as the need be, to allow functional movement of the upper limb.
	1. Joint classification: Plane (gliding) joint with an articular disk.
	2. Supporting ligaments (Netter: 398): a. Acromioclavicular ligament: forms the superior capsule of the AC joint. The capsule then continues around the AC joint itself with the formation of 2 small anterior and posterior AC ligaments. b. Coracoclavicular ligament: consists of the conoid ligament (medial) and the trapezoid ligament (lateral), which bind the scapula to the clavicle. When the head of the clavicle rotates forward at the SC joint, the lateral clavicle elevates (because of the "S" shape, which tenses the coracoclavicular ligament and, in turn, helps elevate the scapula; thus shoulder girdle elevation occurs).
Scapulothoracic joint (Netter: 170): not a true joint (sometimes referred to as a "false" or "pseudo" joint) and is formed by the scapula as it glides over the posterior thorax. Movements include: elevation (approximately 60 degrees- 80 degrees measured at the acromion process); depression (approximately 5-10 degrees); protraction (abduction)/retraction (adduction) (approximately 30 degrees total movement- as measured at the SC joint). A circular movement may also be produced by combining all these movements. The scapula is connected to the clavicle via the coracoclavicular ligament, and thus, moves in conjunction with the clavicle. The scapulothoracic joint is primarily supported by the serratus anterior (Netter: 177, 178). Loss of the serratus anterior (i.e. long thoracic nerve injury) produces "scapular winging".
Coracoacromial ligament: The coracoacromial ligament is stretched between the coracoid process and the acromion and completes, with the acromion and clavicle, a bony-ligamentous arch which covers the head of the humerus. The coracoacromial ligament is triangular in shape, with its base arising from the coracoid process. It is relatedabove to the clavicle and deltoid; below to the subacromial bursa and the tendon of the supraspinatus. Along with the bony structures, the coracoacromial ligament creates a passageway for the exit of the supraspinatus (supraspinatus outlet), as it leaves its scapular origin to insert on the greater tuberosity of the humerus. Via its attachments, the coracoacromial ligament further stabilizes and anchors the acromion; irritation of the subacromial bursa by this ligament can also produce subacromial bursitis.