Logan Steele
The scapula, or shoulder blade, is a sturdy, flat, triangular bone that sits above the rib cage in the upper back. It has six types of motion, which allow for full-functional upper extremity movement. These motions are protraction, retraction, elevation, depression, upward rotation, and downward rotation. The scapula's stability is dependent on the surrounding musculature, with several muscles attaching directly to it. These muscles include the levator scapulae, trapezius, rhomboids, serratus anterior, and pectoralis minor. The scapula also has intrinsic and extrinsic muscles. The intrinsic muscles of the scapula include the rotator cuff muscles, while the extrinsic muscles include the triceps, biceps, and deltoid.
| Characteristics | Values |
|---|---|
| Bones | Shoulder blade; sits above the rib cage in the upper back |
| Joint | Shoulder joint; connects the clavicle to the humerus |
| Shape | Sturdy, flat, triangular |
| Nerves | Dorsal scapular, upper and lower subscapular, and suprascapular nerves |
| Muscles | Intrinsic: rotator cuff muscles, teres major, subscapularis, teres minor, infraspinatus, levator scapulae, rhomboids, serratus anterior |
| Extrinsic: triceps, biceps, deltoid | |
| Third group: levator scapulae, trapezius, rhomboids, serratus anterior | |
| Protraction | Serratus anterior, pectoralis major, pectoralis minor |
| Retraction | Trapezius, rhomboids, latissimus dorsi |
| Elevation | Trapezius, levator scapulae, rhomboid |
| Depression | Latissimus dorsi, serratus anterior, pectoralis major and minor, trapezius |
| Upward rotation | Trapezius, serratus anterior |
| Downward rotation | Latissimus dorsi, levator scapulae, rhomboids, pectoralis major and minor |
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What You'll Learn
The role of the serratus anterior
The serratus anterior is a fan-shaped muscle located at the lateral wall of the thorax. It originates from the first to eighth or ninth rib and inserts at the anterior surface of the scapula. The muscle is divided into three parts: the superior, intermediate, and inferior. The superior part extends from the first to the second rib to the superior angle of the scapula. The intermediate part extends from the second to the third rib to the medial border of the scapula. The inferior part extends from the fourth to the eighth or ninth rib to the medial border and inferior angle of the scapula.
The serratus anterior has several important functions. Firstly, it is responsible for protraction and upward rotation of the scapula, allowing for overhead lifting and a full range of motion in the shoulder. When the serratus anterior is weakened or impaired, scapular protraction and upward rotation are affected, reducing shoulder stability and increasing the risk of injury. Secondly, the serratus anterior actively stabilizes the scapula within the shoulder complex. It works in conjunction with other muscles, such as the upper and lower trapezius fibres, to maintain the position of the scapula and prevent dislocation. Thirdly, the serratus anterior assists in respiration by lifting the rib cage and supporting breathing, particularly during periods of respiratory distress.
The serratus anterior is vulnerable to injury and pain, especially in sports with repetitive motions such as swimming, tennis, or weightlifting. Damage to the long thoracic nerve, which supplies innervation to the serratus anterior, can result in weakness or paralysis of the muscle. This can lead to scapular winging and an increased risk of subacromial impingement syndrome.
The serratus anterior is also known as the "boxer's muscle" due to its role in protraction of the scapula during the throwing of a punch. Additionally, it has been referred to as the "big swing muscle," highlighting its importance in generating power and stability during overhead movements.
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The trapezius and scapular movement
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. The scapula can move in six directions, each produced by specific primary muscles. These movements are protraction, retraction, elevation, depression, upward rotation, and downward rotation.
The trapezius is a large, triangular, broad, and thin muscle that covers the upper back, shoulders, and neck. It is a paired trapezoid-shaped surface muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae of the spine and laterally to the spine of the scapula. The trapezius has upper, middle, and lower groups of fibres. The upper fibres can elevate and upwardly rotate the scapula and extend the neck. The middle fibres adduct (draw together) the scapulae. The lower fibres depress the scapula and aid the upper fibres in upwardly rotating it. The trapezius also assists in scapular retraction and abduction of the shoulder above 90 degrees.
The trapezius works with other muscles to produce scapular movement. For example, the serratus anterior works in conjunction with the lower trapezius to rotate the scapula upward during arm elevation. The levator scapulae works with the upper trapezius to lift and rotate the shoulder. The pectoralis minor assists the trapezius in stabilising the scapula by drawing it forward and downward against the thoracic wall. The latissimus dorsi works with the lower trapezius to assist in downward rotation of the scapula. The supraspinatus works with the upper trapezius to initiate the first 15 degrees of shoulder abduction.
The trapezius is mainly postural, but it is also used for active movements such as side bending, rotation of the head, elevating and depressing the shoulders, and internally rotating the arm. It is often the first muscle encountered when dissecting a cadaver. The trapezius is also important for shoulder elevation, with the upper trapezius frequently involved in neck injuries. The upper portion of the trapezius can be developed by elevating the shoulders, with exercises such as the hang clean and shoulder shrug. The middle fibres are developed by pulling the shoulder blades together, and the lower part by drawing the shoulder blades downward while keeping the arms almost straight and stiff.
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Rhomboid major and minor
The rhomboid major and minor are a group of deep intrinsic shoulder muscles. They are a collective group of muscles that, together with the sternocleidomastoid, trapezius, pectoralis muscles, latissimus dorsi, and serratus anterior, form the shoulder girdle. The rhomboid minor is a cylindrical muscle that originates at the ligamentum nuchae and C7 and T1 vertebra. It inserts at the scapula's medial border near the base of the spine of the scapula. The rhomboid major is a quadrangular muscle located inferior to the rhomboid minor. The origin of the rhomboid muscles is from the spinous processes of the T2-T5 vertebra and inserts on the medial border of the scapula, just inferior to the rhomboid minor.
Functionally, the rhomboid muscles retract, elevate and rotate the scapula. They also protract the medial border of the scapula, keeping it in position at the posterior thoracic wall. The serratus anterior, trapezius, and rhomboid major and minor work with the rhomboids to anchor the scapula and prevent winging. The main action of the rhomboid muscles is scapular retraction around the scapulothoracic joint. Scapular retraction is a simultaneous sliding of the scapula superiorly and medially along the trunk. This superomedial movement of the scapula rotates the glenoid cavity inferiorly, dropping the shoulder girdle. By opposing excessive scapular protraction, the rhomboids help to maintain a correct posture when sitting, standing and walking.
The rhomboids are important in upper limb movement and stability of both the shoulder girdle and scapula. Both rhomboids receive innervation from the dorsal scapular nerve, and their vascular supply is the dorsal scapular artery. Variants in rhomboid musculature have been found but are very rare. While surgeries of the rhomboid musculature are infrequent, winged scapula and rhomboid palsy are clinical pathologies associated with the rhomboids.
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The levator scapulae
The main function of the levator scapulae is to elevate and retract the shoulder girdle at the scapulothoracic joint. It also helps to prevent the depression of the girdle when carrying heavy loads. When the scapula is fixed, contraction of the levator scapulae leads to the lateral flexion of the cervical vertebral column to the side and stabilizes the vertebral column during rotation. Bilateral contraction of the muscle helps in the extension of the cervical spine.
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Rotator cuff muscles
The rotator cuff is a group of four distinct muscles and their tendons that provide strength and stability to the shoulder complex. They are also referred to as the SITS muscle group, an acronym that refers to the names of the four muscles: the supraspinatus, infraspinatus, teres minor, and subscapularis. These muscles arise from the scapula and connect to the head of the humerus, forming a cuff around the glenohumeral joint.
The rotator cuff muscles are responsible for stabilising the shoulder joint, allowing a wide range of movement while maintaining the stability of the glenohumeral joint. They keep the head of the humerus within the small glenoid fossa of the scapula, enlarging the range of motion in the joint and avoiding mechanical obstruction. This group of muscles is essential for almost every type of shoulder movement, including flexion, abduction, internal rotation, and external rotation.
The supraspinatus 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, making it hardly differentiated from the infraspinatus. The subscapularis originates on the anterior surface of the scapula, also known as the subscapular fossa.
The rotator cuff muscles receive their vascular supply mainly from three arteries: the suprascapular artery, the subscapular artery, and the posterior circumflex humeral artery. Balanced strength and flexibility in each of these four muscles are vital to maintaining the functioning of the entire shoulder girdle.
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Frequently asked questions
The scapula, commonly referred to as the shoulder blade, is the bone that sits above the rib cage in the upper back.
The scapula can move in six directions, each movement is produced by specific, primary muscles. Protraction is accomplished by the serratus anterior, pectoralis major, and pectoralis minor muscles. Retraction is accomplished by the trapezius, rhomboids, and latissimus dorsi muscles.
The intrinsic muscles of the scapula include the rotator cuff muscles, teres major, subscapularis, teres minor, and infraspinatus. The extrinsic muscles include the triceps, biceps, and deltoid. The third group includes the levator scapulae, trapezius, rhomboids, and serratus anterior.
During a shoulder press exercise, the upper trapezius, lower trapezius, and serratus anterior work together to achieve upward rotation. During a cable row, the middle trapezius and rhomboids are engaged in scapular retraction as the shoulder extends.
The scapula serves as the foundation for the humerus, the bone of the upper arm. The proper movement of the scapula is crucial for aligning the glenoid fossa, the shoulder socket, with the head of the humerus. This alignment is essential for maintaining upper limb stability during all types of movements.
