Dominic Stone
The scapula, or shoulder blade, is a sturdy, flat, triangular bone that sits above the rib cage in the upper back. It connects the clavicle to the humerus, forming the posterior of the shoulder girdle and the glenohumeral (shoulder) joint. The scapula can move in six directions, each produced by specific primary muscles. These include the serratus anterior, pectoralis major, pectoralis minor, trapezius, rhomboids, levator scapulae, latissimus dorsi, deltoid, triceps, biceps, and rotator cuff muscles. The rotator cuff muscles include the supraspinatus, infraspinatus, subscapularis, and teres minor.
| Characteristics | Values |
|---|---|
| Number of directions the scapula can move in | 6 |
| Names of the muscles that move the scapula | Serratus anterior, pectoralis major, pectoralis minor, trapezius, rhomboids, latissimus dorsi, levator scapulae, rotator cuff muscles, teres major, subscapularis, teres minor, infraspinatus, supraspinatus, triceps, biceps, deltoid, levator scapulae, rhomboids, serratus anterior |
| Number of muscles attached to the scapula | 17 |
| Names of muscles attached to the scapula | Rotator cuff muscles, teres major, subscapularis, teres minor, infraspinatus, supraspinatus, deltoid, levator scapulae, rhomboids, serratus anterior, latissimus dorsi, biceps brachii, brachialis, triceps brachii, brachioradialis, coracobrachialis, pectoralis major, pectoralis minor, trapezius, rhomboids, teres major, teres minor |
| Nerves to the scapula | Dorsal scapular, upper and lower subscapular, suprascapular nerves |
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What You'll Learn
The intrinsic muscles of the scapula
The scapula, or shoulder blade, is a sturdy, flat, triangular bone that connects the clavicle to the humerus. The scapula forms the posterior of the shoulder girdle. The scapula provides attachment to several groups of muscles, including the intrinsic muscles.
In addition to the rotator cuff muscles, the intrinsic muscles of the scapula include the teres major, which arises from the lower third of the dorsal aspect of the lateral border. The teres major is separated from the infraspinatus muscle by a fibrous septum attached to a ridge on the outer part of the back of the scapula.
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The extrinsic muscles of the scapula
The scapula, or shoulder blade, is a flat, triangular bone that sits above the rib cage in the upper back. It connects the clavicle to the humerus and forms the posterior of the shoulder girdle. The scapula provides attachment points for several groups of muscles, including the extrinsic muscles.
The triceps, one of the extrinsic muscles, originates from the infraglenoid tubercle of the scapula. The long head of the biceps brachii arises from the supraglenoid tubercle, while the short head originates from the lateral part of the tip of the coracoid process.
The deltoid muscle arises from the lower border of the crest of the spine and the lateral border of the acromion. It provides muscular support to the glenohumeral joint, along with the four rotator cuff muscles: the supraspinatus, infraspinatus, subscapularis, and teres minor.
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Protraction, retraction, elevation, depression and rotation
The scapula, or shoulder blade, is a bone that sits above the rib cage in the upper back. It is a sturdy, flat, triangular bone that connects the clavicle to the humerus, forming the posterior of the shoulder girdle. The scapula enables multiple types of motion, including protraction, retraction, elevation, depression, upward rotation, and downward rotation, allowing for a fully functional upper extremity area.
Protraction is the forward movement of the scapula about the thoracic wall (scapulothoracic joint), also known as scapular abduction. This motion is accomplished by the serratus anterior, pectoralis major, and pectoralis minor muscles, with the rhomboid major and minor controlling the rate and range of scapular protraction.
Retraction, the opposite movement of protraction, involves pulling the shoulder blades together toward the spine. It is accomplished by the trapezius, rhomboids, and latissimus dorsi muscles.
Elevation occurs when the upper trapezius and serratus anterior muscles contract, while depression is a passive movement that occurs with the relaxation of the trapezius and levator scapulae, allowing the scapula to drop by the force of gravity. The latissimus dorsi, serratus anterior, pectoralis major and minor, and trapezius muscles also contribute to depression.
Rotation of the scapula can be external or internal. External rotation requires active contraction of the descending and transverse parts of the trapezius muscle, while concurrent contraction of the levator scapulae muscle neutralizes rotation, producing elevation. Internal rotation is also a passive movement, occurring with the relaxation of the trapezius and levator scapulae, and is facilitated by the levator scapulae, rhomboids, and pectoralis minor muscles.
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The rotator cuff muscles
The rotator cuff is a group of four muscles in the shoulder that provide stability to the glenohumeral joint while allowing a wide range of movement. The four muscles are supraspinatus, infraspinatus, teres minor, and subscapularis. These muscles form a musculotendinous cuff around the glenohumeral joint, providing muscular support and stability. They arise from the scapula and connect to the head of the humerus.
The supraspinatus muscle is the only muscle of the rotator cuff that is not a rotator of the humerus. The infraspinatus, on the other hand, is a powerful lateral rotator of the humerus. The teres minor is a narrow and long muscle entirely covered by the deltoid and is hardly differentiated from the infraspinatus. The subscapularis originates on the anterior surface of the scapula, also known as the subscapular fossa.
Injuries to the rotator cuff muscles are common and can occur at any age, often due to trauma or overuse. These injuries can lead to shoulder pain, impaired function, and a reduced quality of life. The most common imaging method to evaluate rotator cuff injuries is MRI, which can detect tears and inflammation to establish a proper treatment protocol.
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The deltoid muscle
The primary function of the anterior deltoid is flexion, internal rotation, and horizontal adduction. To stretch this muscle, the shoulder can be extended, externally rotated, and horizontally abducted. The posterior deltoid, on the other hand, is responsible for extension, external rotation, and horizontal abduction. To stretch the posterior deltoid, the shoulder can be flexed, internally rotated, and horizontally adducted.
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