Synergism of the muscles, tendons and ligaments around the glenohumeral joint.(Literature review)
The Supraspinatus muscle collaborates with several structures, including muscles and ligaments, to effectively stabilize and facilitate movement in the shoulder joint. Below is a detailed breakdown:
Muscles that Work with the Supraspinatus
1. Deltoid Muscle: The supraspinatus initiates arm abduction (0° to 15°) and works in concert with the deltoid to continue abduction beyond this range. As the angle increases, the deltoid becomes increasingly dominant in the abduction process.
2. Other Rotator Cuff Muscles:
– Infraspinatus: Aids in external rotation and stabilizes the humeral head.
– Teres Minor: Contributes to external rotation and stabilization of the humeral head.
– Subscapularis: Helps stabilize the humeral head within the glenoid cavity, counteracting forces during movement.
Ligaments that Support the Supraspinatus
1.Inferior Glenohumeral Ligament (IGHL): Provides passive stabilization by limiting superior and anterior translation of the humeral head, enhancing the stabilizing role of the supraspinatus during abduction.
2. Coracohumeral Ligament: Assists in limiting inferior translation of the humeral head, especially when the arm is adducted, supporting the supraspinatus in maintaining joint stability.
Together, these muscles and ligaments ensure both dynamic and static stability of the shoulder joint while facilitating smooth movements such as abduction and external rotation.
The Subscapularis muscle, an essential component of the rotator cuff, also works synergistically with various muscles and ligaments to stabilize and facilitate movement in the shoulder joint.
Muscles that Work with the Subscapularis
1. Rotator Cuff Muscles:
– Supraspinatus: Helps stabilize the humeral head within the glenoid fossa and complements the subscapularis during shoulder movements.
– Infraspinatus and Teres Minor: Serve as antagonists to the subscapularis by providing external rotation, balancing its internal rotation force. Together, these muscles form a force couple that stabilizes the glenohumeral joint by compressing the humeral head into the glenoid cavity.
2. Latissimus Dorsi: Works synergistically with the subscapularis during internal rotation and adduction of the shoulder, particularly when the function of the subscapularis is compromised.
3. Pectoralis Major: Aids in internal rotation and adduction of the shoulder, complementing the subscapularis during these movements.
4. Deltoid (Anterior Fibers): Contributes to internal rotation alongside the subscapularis and assists in arm elevation.
Ligaments that Support the Subscapularis
1. Coracohumeral Ligament: Reinforces the area between the subscapularis and supraspinatus tendons, providing added stability to the anterior shoulder.
2. Glenohumeral Ligaments (especially the Anterior Band of IGHL): These ligaments limit excessive anterior translation of the humeral head, complementing the stabilizing role of the subscapularis during shoulder movements.
Functional Synergy
– The subscapularis primarily provides internal rotation and prevents anterior displacement of the humeral head while working in conjunction with other rotator cuff muscles to maintain dynamic stability.
– Additionally, it plays a role in “concavity compression,” where opposing forces from the subscapularis (anterior) and infraspinatus/teres minor (posterior) help stabilize the humeral head within the glenoid cavity.
In summary, the subscapularis muscle synergizes with the other rotator cuff muscles—particularly the supraspinatus, infraspinatus, and teres minor—as well as larger muscles such as the latissimus dorsi and pectoralis major. Ligaments like the coracohumeral and glenohumeral ligaments further support its stabilizing functions. Together, these structures ensure proper shoulder mechanics and joint stability during movement.
The Infraspinatus and Teres minor muscles.
This muscles are components of the rotator cuff, primarily function as external rotators of theshoulder joint. They collaborate with various other muscles and ligaments to stabilize and mobilize the shoulder joint effectively.
Synergistic Muscles
1. Rotator Cuff Muscles:
– Supraspinatus: Initiates arm abduction and stabilizes the humeral head, complementing the actions of infraspinatus and teres minor by preventing superior translation of the humeral head.
– Subscapularis: Provides anterior stabilization and counteracts excessive anterior displacement, coordinating with infraspinatus and teres minor to maintain joint stability during movement.
2. Deltoid Muscle:
– The deltoid works alongside the rotator cuff muscles during shoulder abduction. Infraspinatus and teres minor counterbalance the upward pull of the deltoid, preventing superior displacement of the humeral head.
3. Teres Major:
– Although not a rotator cuff muscle, teres major aids with shoulder adduction and internal rotation, complementing the stabilization provided by infraspinatus and teres minor.
4. Trapezius and Serratus Anterior:
– These muscles stabilize the scapula, providing an optimal base for infraspinatus and teres minor to act on the humerus effectively during external rotation and other movements.
Synergistic Ligaments
1. Glenohumeral Ligaments:
– The superior, middle, and inferior glenohumeral ligaments provide passive stability to the shoulder joint. They work alongside the active stabilization role of infraspinatus and teres minor to limit excessive translation of the humeral head.
2. Capsular Mechanoreceptors:
– Mechanoreceptors within the glenohumeral capsule interact with rotator cuff muscles through reflex arcs, enhancing their synergistic action to stabilize the joint during dynamic movements.
Functional Roles
– Infraspinatus and teres minor work together to externally rotate the humerus, stabilize the glenohumeral joint by compressing the humeral head into the glenoid cavity, and counteract anterior or superior translation forces during arm movements.
– During overhead activities, these muscles help clear the greater tuberosity from impinging under the coracoacromial arch by externally rotating the humerus.
In summary, infraspinatus and teres minor synergize with other rotator cuff muscles (such as supraspinatus and subscapularis), larger movers like the deltoid and trapezius, and passive stabilizers like the glenohumeral ligaments to guarantee stability, mobility, and proper biomechanics of the shoulder joint.