Capsuloligamentous Constraint.

Figure 1 - Maximum humeroscapular angle

Figure 2 - Amount of internal and external rotation

About capsuloligamentous constraint

What is the purpose of the capsule and ligaments of the glenohumeral joint?

The capsule and ligaments of the glenohumeral joint serve as check reins to glenohumeral translation and rotation. They are not "primary stabilizers" in that they do not effectively hold the humeral head centered in the glenoid socket in most functional positions of the joint.

The capsule and its ligaments arise in continuity with the articular surface of the glenoid through the glenoid labrum, so that when they are under tension they provide a smooth continuation of the glenoid concavity. By serving as check reins at the limits of glenohumeral motion, the capsule and ligaments control the maximum humeroscapular angle that can be achieved in a given direction as well as the amount of internal and external rotation that is allowed at each humeroscapular position. For example, the posterior capsule limits how far the elevated arm can be brought across the body. Glenohumeral joints with lax posterior capsules can reach the 90 degree anterior humeroscapular plane. Shoulders with tight posterior capsules have difficulty reaching the 45 degree anterior humeroscapular plane. Similarly, the anterior capsule limits posterior motion of the elevated arm. Shoulders with anterior capsular laxity achieve significantly more posterior humeroscapular planes than shoulders with tight anterior structures. In this way, the capsule prevents the humerus from deviating far from positions of glenohumeral balance.

Certain portions of the capsular complex that serve major roles are condensed and thickened in the form of capsular ligaments. These ligaments appear to represent capsular reinforcements in directions where large torques may be encountered at the extremes of motion, as in swinging from branch to branch or in the transition between the cocking and the acceleration phases in a baseball pitch. These motions apply major torques to the joint. The strong anterior band of the inferior glenohumeral ligament is strategically positioned to check the range of rotation of the joint when the arm is elevated and forced into external rotation.

Movies

• The capsule (0.24 MB)
• The ligaments (2.61 MB)

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