Logan Steele
The shoulder joint, or glenohumeral joint, is a ball-and-socket joint that allows for a wide range of movements. Several muscles are involved in elevating the shoulders, including the trapezius, levator scapulae, and rhomboid muscles. The trapezius is a large triangular muscle at the back of the shoulder, while the levator scapulae is a small strap-like muscle that begins in the neck and attaches to the scapula. The rhomboid muscles, consisting of the rhomboid major and minor, stretch from the top of the spine to the scapula and help elevate the shoulder blade. Additionally, the deltoid muscle, located on the outside of the shoulder, assists in arm abduction and lateral rotation.
| Characteristics | Values |
|---|---|
| Muscle | Trapezius |
| Location | Back part of neck and shoulders, partway down spine |
| Shape | Broad, flat, triangular |
| Function | Elevation and depression of the shoulder |
| Muscle | Deltoid |
| Location | Outside of the shoulder |
| Shape | Large, triangular |
| Function | Flexion, abduction, extension, lateral rotation of the arm |
| Muscle | Levator scapulae |
| Location | Neck |
| Shape | Small, strap-like |
| Function | Elevates the scapula |
| Muscle | Rhomboids |
| Location | Back |
| Shape | N/A |
| Function | Elevate the shoulder blade |
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What You'll Learn
Trapezius
The trapezius muscle is a large, paired, trapezoid-shaped muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae of the spine and laterally to the spine of the scapula. It is one of the broadest and most superficial (closest to the skin) muscles of the upper back and trunk. The trapezius is triangular, broad, and thin; it covers the upper back of the shoulders and neck. It is often referred to as the 'traps' or 'trap muscles'.
The trapezius muscles originate from the superior aspect of the nuchal line in the occipital, cervical, and upper thoracic region and insert at the lateral aspect of the clavicle, the acromion, and spine of the scapula. The trapezius muscles get their name from their shape, as they form a trapezoid (a shape with four sides, two of which are parallel) when viewed together. The upper, middle, and lower trapezius fibres work together to elevate and upwardly rotate the scapula, as well as extend the neck.
The upper trapezius fibres originate from the external occipital protuberance, the superior nuchal line of the occipital bone, and the ligamentum nuchae. They proceed downward and laterally to insert into the posterior border of the lateral third of the clavicle. The upper trapezius fibres are responsible for extending the head at the neck and elevating the scapula.
The middle trapezius fibres arise from the spinous process of the seventh cervical and the spinous processes of the first, second, and third thoracic vertebrae. They insert into the medial margin of the acromion and the superior lip of the posterior border of the spine of the scapula. The middle trapezius fibres adduct (medially retract) the scapulae, drawing them together and straightening the middle back and arms.
The lower trapezius fibres, or the inferior fibres, arise from the spinous processes of the remaining thoracic vertebrae (T4–T12). They proceed upward and laterally to converge near the scapula and end in an aponeurosis, which glides over the smooth triangular surface on the medial end of the spine. The lower trapezius fibres depress the scapula and aid the upper fibres in upwardly rotating it.
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Deltoid
The deltoid muscle is a large triangular muscle that forms the rounded contour of the human shoulder. It is also referred to as the 'common shoulder muscle' and is located on the outside of the shoulder. It is composed of three distinct sets of muscle fibres: the anterior or clavicular part (commonly known as the front delt), the posterior or scapular part (commonly known as the rear delt), and the intermediate or acromial part (commonly known as the side delt). The deltoid muscle is responsible for flexion and medial rotation of the arm, as well as arm abduction, extension, and lateral rotation. It helps to lift the arm to the front, side, and back, and is crucial for shoulder stability and motion.
The deltoid muscle is a key player in elevating the arm in the scapular plane, and its contraction elevates the humeral head. It works in conjunction with other shoulder muscles, such as the rotator cuff muscles, to enable a wide range of movements. The deltoid's role in arm abduction is particularly notable. When the three parts of the deltoid contract simultaneously, it assists in abducting the arm past 15 degrees. The deltoid cannot initiate abduction independently, but it plays a supporting role by stabilising the arm during the movement.
The deltoid muscle is susceptible to various conditions, including tears, fatty atrophy, and enthesopathy. Deltoid tears are often associated with traumatic shoulder dislocations or massive rotator cuff tears. Additionally, deltoid muscle pain can affect individuals who perform repetitive overhead arm movements, such as swimmers and pitchers. Conditions like adhesive capsulitis (frozen shoulder) and bursitis can also impact the deltoid muscle, causing pain, stiffness, and inflammation in the shoulder joint.
The deltoid muscle is a critical component of shoulder anatomy, enabling a wide range of arm movements and providing stability to the shoulder joint. Its unique structure, with three distinct parts, allows it to function in multiple planes of motion and contribute to the shoulder's overall flexibility and strength.
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Rhomboid major
The rhomboid major is a flat, broad, trapezoid/quadrangular muscle located in the back, deep to the trapezius muscle. It is one of the two rhomboid muscles, the other being the rhomboid minor, which is located superiorly to the rhomboid major. The rhomboid major originates from the spinous processes of the T2-T5 vertebrae and attaches to the medial border of the scapula, between the scapula spine and inferior angle. The muscle fibres extend obliquely in an inferolateral direction. The attachment occurs on both the dorsal and costal aspects of the medial border of the scapula.
The rhomboid major, along with the rhomboid minor, are a group of deep intrinsic shoulder muscles that form the shoulder girdle. These muscles are important for the movement of the upper extremity and stabilization of the shoulder through articulation with the trunk. The main function of the rhomboid major is scapular retraction, which involves sliding the scapula superiorly and medially along the trunk, rotating the glenoid cavity inferiorly, and dropping the shoulder girdle. This muscle also helps to elevate, protract, and rotate the scapula, keeping it in position at the posterior thoracic wall.
The rhomboid major is innervated by the dorsal scapular nerve (DSN), which originates from the ventral ramus of the spinal nerve root C5. The muscle receives arterial blood from three sources: the dorsal scapular artery, the deep branch of the transverse cervical artery, and the dorsal branch of the upper five or six posterior intercostal arteries. These blood vessels ultimately stem from the thyrocervical trunk.
The rhomboid major is susceptible to injuries, especially in individuals who do not exercise regularly or have incorrect shoulder placement during activities such as sports or carrying heavy objects. Weakness in the rhomboid major can lead to strains and tears, resulting in pain that generally extends from the edge of the shoulder blades to the spine.
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Levator scapulae
The levator scapulae is a posterior axio-appendicular muscle that connects the upper limb to the vertebral column. It is located in the posterior triangle of the neck, with its superior part covered by sternocleidomastoid and its inferior part by the trapezius. The levator scapulae originates on the posterior tubercle of the transverse process of cervical vertebrae 1 to 4, and inserts onto the vertebral margin of the scapula between the superior angle and the root of the spine.
The levator scapulae is innervated by 2-3 branches of the 3rd and 4th cervical nerves and frequently by a branch from the dorsal scapular nerve. It is supplied by the dorsal scapular artery, which typically has a small branch supplying the muscle by passing laterally to the supraspinatus fossa of the scapula. The levator scapulae functions to elevate the scapula and tilt the glenoid cavity inferiorly by rotating the scapula downward. When the scapula is fixed, contraction of the levator scapulae leads to lateral flexion of the cervical vertebral column to the side and stabilizes the column during rotation.
When the cervical spine is fixed, the levator scapulae elevates and rotates the scapula, moving the lateral angle inferiorly. In this scenario, contraction of the muscle laterally flexes and rotates the neck to the same side. Bilateral contraction of the levator scapulae contributes to the extension of the cervical spine. Additionally, when the shoulder is fixed, the levator scapulae rotates to the same side and flexes the cervical spine laterally.
The levator scapulae is clinically significant in assessing and treating various conditions. For example, its length and tension can be evaluated by positioning a patient in a supine position and manipulating the head and neck. Furthermore, the levator scapulae is associated with levator scapulae syndrome, characterised by tenderness over the upper medial angle of the scapula. This condition can be effectively treated with physical therapy and local corticosteroid injections.
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Serratus anterior
The serratus anterior (SA) is a fan-shaped muscle that originates on the superolateral surfaces of the first to eighth or ninth ribs at the lateral wall of the thorax. It then wraps posteromedially around the ribcage, passing beneath the scapula to insert on the underside of the scapula on its medial border. The serratus anterior is divided into three parts: upper/superior, middle/intermedius, and lower/inferior.
The upper part extends from the first and second ribs to the superior angle of the scapula. The middle part extends from the second and third ribs to the medial border of the scapula. The lower part is the most powerful and prominent part of the muscle, extending from the fourth to ninth ribs to the medial border and inferior angle of the scapula.
The serratus anterior acts as a prime mover in scapular protraction and scapular upward rotation. It is also a key scapular stabiliser, keeping the shoulder blades against the rib cage when at rest and during movement. This muscle is occasionally called the "big swing muscle" or the "'boxer's muscle' because it is responsible for the protraction of the scapula, or the pulling of the scapula forward and around the rib cage, which occurs when throwing a punch.
The serratus anterior also works with the upper and lower fibres of the trapezius muscle to sustain upward rotation of the scapula, which allows for overhead lifting. In addition, when the shoulder girdle is fixed, all three parts of the serratus anterior muscle work together to lift the ribs, assisting with respiration.
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Frequently asked questions
The trapezius, levator scapulae, and rhomboid muscles are responsible for elevating the shoulder blade.
The trapezius is a large triangular muscle at the back of the shoulder. It is responsible for elevating and depressing the shoulder blade and rotating it during arm abduction.
The levator scapulae is a small strap-like muscle that begins in the neck and descends to attach to the scapula. It elevates the scapula and is responsible for rotational movements and stabilization of the scapula.
