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The scapula, or shoulder blade, is a flat, triangular-shaped bone that sits above the rib cage in the upper back. It is responsible for six types of motion, allowing for full-functional upper extremity movement. The scapula's stability is dependent on the surrounding musculature, with several muscles that attach directly to it. The levator scapulae, a long and slender muscle, is one of the muscles responsible for lifting the scapula. It extends from the transverse processes of vertebrae C1-C4 to the medial border of the scapula.
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What You'll Learn
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 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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Rhomboids major and minor
The rhomboid muscles, comprising the rhomboid major and rhomboid minor, are a group of deep intrinsic shoulder muscles that form the shoulder girdle. They are located deep to the trapezius muscle, with the rhomboid minor partially overlapping the superior portion of the rhomboid major. The rhomboid major is a thin, flat, quadrilateral muscle that is twice as wide as the thicker rhomboid minor.
The rhomboid major originates from the spinous processes of the second to fifth thoracic vertebrae (T2-T5) and the supraspinous ligament. It inserts onto the lower portion of the medial border of the scapula, specifically between the scapular spine and the inferior angle. The rhomboid minor, on the other hand, originates from the nuchal ligament and spinous processes of the seventh cervical (C7) and first thoracic (T1) vertebrae. It inserts into the base of the medial end of the spine of the scapula, with its dorsal layer attaching dorsolaterally and inferiorly to the levator scapulae.
These muscles work together to perform several functions. Firstly, they retract the scapula, pulling it towards the vertebral column. Additionally, they act to elevate and rotate the scapula, ensuring it remains in position at the posterior thoracic wall. By working in conjunction with other muscles, such as the levator scapulae, the rhomboids help to elevate the medial border of the scapula and prevent scapular winging.
The rhomboids are innervated by the dorsal scapular nerve (C4-C5), a branch of the brachial plexus. They receive their arterial blood supply from three sources: the dorsal scapular artery and the deep branch of the transverse cervical artery.
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Serratus anterior
The serratus anterior 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 rib cage, passing beneath the scapula to insert on the underside of the scapula on its medial border.
The serratus anterior is a key scapular stabiliser, keeping the shoulder blades against the rib cage when at rest and during movement. It is the prime mover in both scapular protraction and scapular upward rotation. The upward rotation of the scapula allows for overhead lifting.
The serratus anterior is also known as the "boxer's muscle" because it is largely responsible for the protraction of the scapula, a movement that occurs when throwing a punch.
The serratus anterior is divided into three parts according to the points of insertion: serratus anterior superior (insertion near the superior angle), serratus anterior intermediate (insertion along the medial border), and serratus anterior inferior (insertion near the inferior angle). The lowest four digitations of the serratus anterior interdigitate with the fibres of the external oblique.
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Trapezius
The trapezius muscle is a large, paired muscle in a trapezoid shape, located in the upper back. The muscle gets its name from its shape, resembling a kite or a trapezium. The trapezius is made up of long muscle fibres that span a large width of the upper back. This muscle is used a lot throughout the day and is involved in several movements.
The trapezius is responsible for several functions, including maintaining and adjusting posture, moving the head, neck and upper back, and supporting the spinal column. The muscle also assists in scapular rotation and stabilisation, working with other muscles such as the rhomboids, levator scapulae, serratus anterior, deltoid and latissimus dorsi.
The trapezius has three sections: upper, middle and lower. The upper section connects to the skull and neck, while the middle and lower sections attach to the bones in the thoracic spine and the scapula. The trapezius muscle is controlled by the spinal accessory nerve, which allows for its movement.
In terms of exercises, the trapezius can be targeted through exercises such as the cheerleader exercise, seated rows, and high rows. The upper trapezius can be developed through exercises such as the clean, hang clean, shoulder shrug, and neck extension. The middle fibres are targeted by pulling the shoulder blades together, and the lower trapezius is engaged by drawing the shoulder blades downward with almost straight and stiff arms.
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Pectoralis minor
The pectoralis minor is a thin, triangular muscle located under the pectoralis major. Together, they form the anterior wall of the axilla. The pectoralis minor originates from the margins of the third to fifth ribs, near the costal cartilage. Its fibres pass upward and laterally to insert into the medial border and superior surface of the coracoid process of the scapula.
The pectoralis minor is clinically important and serves as a surgical landmark. This is due to the structures that lie beneath the muscle and its tendon. The nerves and blood supply to the upper limb run deep to the pectoralis minor. These include the posterior, lateral, and medial cords of the brachial plexus. The medial pectoral nerve pierces the pectoralis minor, and it receives innervation from the medial and lateral pectoral nerves. The pectoralis minor also receives vascular supply from the thoracoacromial artery, superior thoracic artery, and lateral thoracic artery.
The pectoralis minor is involved in the movement of the scapula. It depresses the point of the shoulder, drawing the scapula towards the thorax and throwing its inferior angle posteriorly. When the ribs are immobilized, the pectoralis minor brings the scapula forward. It also acts as an accessory muscle of inspiration during respiration.
A shortened pectoralis minor can cause issues such as pain and restricted movement in the neck and upper back. It can also restrict flexion of the shoulder joint by limiting scapular rotation. This abnormal tension can further lead to thoracic outlet syndrome, where the muscle impinges on the brachial plexus and axillary blood vessels, causing shoulder impingement.
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Frequently asked questions
The scapula, or shoulder blade, is the bone that sits above the rib cage in the upper back. It connects the clavicle to the humerus, forming the shoulder joint.
The levator scapulae, a superficial muscle in the back, is primarily responsible for lifting the scapula.
Yes, the trapezius, rhomboids, serratus anterior, serratus posterior superior, and serratus posterior inferior muscles also contribute to the scapula's motion.
Optimal scapula motion is crucial for proper shoulder alignment and upper extremity motion. Knowledge of scapular anatomy is essential for sports medicine professionals and designing advanced exercise programs.
