Posted on 11 May 2010 21:12
By Ground Up Strength
There is a big problem with information about the shoulder. It's not just one joint.
To be more precise, there is one joint that we call the "shoulder joint" but it doesn't act alone. Eric Beard will take us through a video ride to simplify these complex seeming details of the shoulder but I will begin with a bit of explanation first.
The shoulder joint itself is known as the glenohumeral joint. It is a multi-axial ball and socket enarthrodial joint. This joint is the articulation between the glenoid fossa of the scapula and the head of the humerus. This is the area that most people think of as the shoulder joint. The humerus is, however, one bone of the shoulder.
No complete movement of the glenohumeral joint can occur without accompanying movement of the shoulder girdle. The shoulder girdle is formed from the back by the scapula and from the front by the clavicle bones, and these bones tend to move as a unit. Unlike the pelvic girdle, however, the shoulder girdle is not complete. There is no bony link of the scapula to the rest of the skeleton and the scapula do not meet with each other. Since the humerus is articulated with the scapula there is therefore no bony link of the humerus to the axial skeleton.
The shoulder girdle (or pectoral girdle) is made up of three joints. The sternoclavicular (SC), acromioclavicular joint (AC), and the scapulothoracic joint. Sometimes movements of the shoulder girdle are confused with movements of the shoulder joint so the terminology can be confusing. See the table below to differentiate the movments terms between the shoulder joint and the shoulder girdle.
1. The sternoclavicular (SC) is a multiaxial arthrodial, gliding, or plane joint. As its name implies this is the articulation of the clavicle and sternum.
2. The acromioclavicular joint (AC) is also a gliding joint and is the articulation of the clavicle with the acromion process of the scapula. This is the "top" of the shoulder and is the area that most people think of as the shoulder proper, as opposed to the shoulder joint.
3. The scapulothoracic joint is not really a true synovial joint. This is simply the scapula's relationship with the thorax. The scapula has no ligamentous support and it is only supported by its muscles. It has no independant movement but its movement occurs as a result of motion at the SC and AC joints. It may not be proper to think of the scapulothoracic as a joint but thinking of it this way, as part of the three joints of the shoulder girdle, helps us remember the primary importance of the scapula and its muscles in all movement of the shoulder.
For a much more comprehensive description of thes shoulder complex joints see by Joint Structure and Function: A Comprehensive Analysis, by Pamela K. Levangie, et al.
Together the shoulder joint (glenohumeral) and the shoulder girdle make up the shoulder complex. The movement and health of this complex must be considered together. The videos and the accompanying tables, therefore, are not just about the deltoids!
The rotator cuff is a very important group of muscles that are intrinsic to the glenohumeral joint: the subscapularis, infraspinatus, supraspinatus, and teres minor. These muscles are of primary importance in maintaining dynamic stability of the shoulder joint.
Pairing of Shoulder Joint Movements and Associated Shoulder Girdle Movements
|Shoulder Joint||Shoulder Girdle|
|Flexion||Elevation & Upward Rotation|
|Extension||Depression & Downward Rotation|
* sometimes refered to as abduction
** sometimes refered to as adduction
Eric Beard, a great corrective exercise specialist out of Boston has agreed to make some videos exploring the shoulder complex. Actually, I asked him just to make a video demonstrating the movements and he instead has begun a series of seven videos on the shoulder complex, which he calls "short". Yep, GUS is not the only one with the motto "if it's worth doing it's worth overdoing". For more shoulder information you are going to want to check out Eric's site theAthleticShoulder.com
Video One: Shoulder Complex Arthrokinematics by Eric Beard
Here Eric starts with the movements of the shoulder joint, including flexion, extension, abduction, adduction, internal rotation (or medial rotation), external rotation (or lateral rotation) and horizontal adduction and abduction. These shoulder joint movements, he says, have a great deal of mobility but not much stability. This is one of the central features of the shoulder. It has such a wide range of motion in so many different planes and that comes with a price: reduced stability.
From there he shows us how to palpate the sernoclavicular joint. He explains that there should be some subtle movements of the sternoclavicular joint during various movements of the shoulder. For instance you should find some elevation and depression of the SC joint when your arm is abducting and adducting and some protraction and retraction of the joint during horizontal abduction and adduction of the shoulder joint. If there is not enough movement of the sternoclavicular the acromioclavicular joint, in Eric's words, gets beat up. You've probably heard of AC joint injuries as this is the most commonly separated joint of the shoulder complex.
The movements of the scapulothoracic joint comes next and you can see these movements in the table above. The pairings of the shoulder joint movements with the shoulder girdle movements are more specifically pairings of the shoulder joint with the scapulothoracic. Most of the time "the scapula" rather than the SC joint is refered to when discussing these movements but, even though it is not a "true" joint, as stated above, it is best to think of it in those terms.
Video Two: Shoulder Joint Range of Motion by Eric Beard
This second video deals with the various ranges of motion of the shoulder complex. Eric begins by re-emphasizing the importance of sternoclavicular joint movement. Apparently this is an area that is often ignored.
Sternoclavicular Ranges of Motion
- Retraction (moving toward the body)
- Protraction (moving away from the body) - 15 to 30°
- Depression - 10°
- Elevation - 45°
*Posterior Rotation - 10 to 45°
The sternoclavicular does not move on its own. The scapula must move to initiate movement at the SC.
Glenohumeral (Shoulder Joint) Ranges of Motion
- Flexion - 165 to 180°
- Extension - 35 to 60° (Eric notes that most do not have this range of motion in extension)
- Abduction - 180° (about one-third of this from the glenohumeral alone and two-third from the scapulothoracic joint)*
- External Rotation - 90°
- Internal Rotation - 70°**
* the movement of the scapulothoracic and the glenohumeral which occurs together is refered to as "scapulo-humeral rhythm". Remember that the clavicle must be moving as well.
** when checking for internal and external rotation of the shoulder note that you should be doing it passively. Notice while demonstrating internal rotation range of motion that Eric just lets his arm hang. He does not force it down further. So this is "passive" meaning that you are not actively trying to extend the range of motion through muscular force which would be "active"
Check back for more videos to come!
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This page created 11 May 2010 21:12
Last updated 22 Feb 2015 17:07