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The scapula, also known as the shoulder blade, is a flat, triangular bone located at the back of the trunk, over the posterior surface of ribs two to seven. The scapula provides a point of attachment for a number of muscles that make up the arm and shoulder. There are 17 muscles that attach to the scapula, including the deltoid, latissimus dorsi, trapezius, serratus anterior, and biceps brachii. The scapula also articulates with the humerus and clavicle, forming the glenohumeral (shoulder) joint and acromioclavicular joint, respectively. The stability of the scapula depends on the surrounding musculature, and any disturbance in the rhythm of its movement can lead to fatigue, impingement, instability, and limited elevation.
| Characteristics | Values |
|---|---|
| Number of muscles attached to the scapula | 17 |
| Description of the scapula | Flat, triangular-shaped bone |
| Location of the scapula | Upper thoracic region on the dorsal surface of the rib cage |
| Functions of the scapula | Connects with the humerus at the glenohumeral joint, also connects with the clavicle at the acromioclavicular joint to form the shoulder joint |
| Types of muscles | Intrinsic, extrinsic, and rotator cuff muscles |
| Intrinsic muscles | Rotator cuff muscles, teres major, subscapularis, teres minor, and infraspinatus |
| Extrinsic muscles | Triceps, biceps, and deltoid |
| Third group of muscles | Levator scapulae, trapezius, rhomboids, and serratus anterior |
| Functions of the third group of muscles | Rotational movements and stabilization of the scapula |
| Movements of the scapula | Protraction, retraction, elevation, depression, upward rotation, and downward rotation |
| Muscles responsible for protraction | Serratus anterior, pectoralis major, and pectoralis minor |
| Muscles responsible for retraction | Trapezius, rhomboids, and latissimus dorsi |
| Muscles responsible for elevation | Upper trapezius and levator scapulae |
| Muscles responsible for depression | Lower trapezius |
| Muscles responsible for upward rotation | Upper and middle trapezius |
| Muscles responsible for downward rotation | Rhomboids |
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What You'll Learn
The four rotator cuff muscles
The scapula, or shoulder blade, is a flat, triangular-shaped bone that connects the clavicle to the humerus. There are 17 muscles that attach to the scapula, and four of these make up the rotator cuff. These four muscles are the supraspinatus, infraspinatus, subscapularis, and teres minor. The rotator cuff muscles act to stabilize the glenohumeral joint.
The supraspinatus muscle is responsible for abduction at the shoulder joint and is innervated by the suprascapular nerve. It originates from the supraspinous fossa, which is the superior portion of the posterior side of the scapula. The infraspinatus muscle, on the other hand, originates from the infraspinous fossa, which is the inferior portion of the posterior side of the scapula. It is involved in lateral rotation at the shoulder joint. The infraspinatus muscle is supplied by the posterior circumflex humeral artery, a branch of the axillary artery.
The subscapularis muscle originates on the anterior surface of the scapula, also known as the subscapular fossa. This muscle is one of the intrinsic muscles of the scapula, attaching directly to the surface of the bone. The subscapular fossa is a large concavity on the ventral surface of the scapula, allowing for the attachment of the subscapularis muscle via three ridges within this fossa.
The teres minor muscle is one of the smaller muscles of the scapula. It is part of the rotator cuff, working together with the other three muscles to stabilize the shoulder joint. The teres minor muscle also assists with abduction and external and internal rotation of the glenohumeral joint.
Injuries to the rotator cuff muscles are common, especially in individuals who frequently use their shoulders for overhead motions, such as pitchers or swimmers. It is important to rest and stretch the shoulder muscles properly to prevent injuries and maintain their flexibility and strength.
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The extrinsic muscles
The scapula, or shoulder blade, is a flat, triangular bone that connects the clavicle to the humerus. It has 17 muscles attached to it, including three groups of extrinsic muscles. These extrinsic muscles attach to the processes of the scapula and affect motion at the glenohumeral joint.
The first group of extrinsic muscles includes the triceps, biceps, and deltoid. The deltoid muscle is on the outside of the shoulder and helps move the arm forward, backward, and to the side. The long head of the biceps brachii arises from the supraglenoid tubercle, while the long head of the triceps arises from the infraglenoid tubercle.
The second group of extrinsic muscles consists of the levator scapulae, trapezius, rhomboids, and serratus anterior. These muscles are responsible for rotational movements and stabilization of the scapula. The levator scapulae inserts along the dorsal aspect of the medial border, from the superior angle up to the root of the spine. The upper trapezius and levator scapulae raise the scapula, while the lower trapezius brings it down. The rhomboids and middle trapezius enable retraction, or adduction, by separating the scapula from the thoracic wall during rowing motions. The serratus anterior, on the other hand, facilitates protraction or abduction by bringing the scapula against the thoracic wall when reaching forward.
The third group of muscles includes the pectoralis major and pectoralis minor. The pectoralis minor inserts into the medial border and superior surface of the coracoid process. These muscles work together with the serratus anterior and levator scapulae to enable protraction, or the forward movement of the scapula.
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The levator scapulae
The main function of the levator scapulae is to elevate the scapula and tilt the glenoid cavity inferiorly by rotating the scapula downward. It also acts to stabilize the vertebral column during rotation. If the cervical spine is fixed, contraction of the levator scapulae helps in elevating and rotating the scapula, such that the lateral angle moves inferiorly (rotates the point of the shoulder down). When the scapula is stabilized, contraction of this muscle laterally flexes and rotates the neck to the same side. Bilateral contraction helps in the extension of the cervical spine.
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The rhomboid muscles
The rhomboid major is a broad, quadrilateral muscle that originates from the spinous processes of the second to fifth thoracic vertebrae (T2-T5). It extends obliquely and inserts into the medial border of the scapula, between the inferior angle and the root of the spine. The rhomboid major is innervated by the dorsal scapular nerve and receives arterial blood from the dorsal scapular artery. It performs actions such as elevation and retraction of the scapula.
The rhomboid minor, on the other hand, is a small, cylindrical muscle that originates from the nuchal ligament and the spinous processes of the seventh cervical (C7) and first thoracic (T1) vertebrae. It extends obliquely and inserts into the base of the medial end of the spine of the scapula, with the dorsal layer attaching dorsolaterally and the ventral layer inserting inferomedially. The rhomboid minor is also innervated by the dorsal scapular nerve and shares the same arterial blood sources as the rhomboid major. It performs similar functions of elevation and retraction of the scapula.
Both the rhomboid major and minor muscles work together to stabilize the scapula and reinforce the shoulder. They are considered extrinsic back muscles and are important for the overall movement and stability of the upper extremity.
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The serratus anterior
The contraction of the serratus anterior leads to an anterolateral movement of the scapula along the ribs. The pull of the inferior part at the lower scapula shifts the shoulder joint superiorly, enabling the lifting of the arm above 90 degrees (elevation). Conversely, the superior part depresses the scapula. The serratus anterior also actively stabilises the scapula within the shoulder.
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