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The scapula, commonly referred to as the shoulder blade, is a flat, triangular bone that sits above the rib cage in the upper back. It connects the clavicle to the humerus, forming the shoulder joint. The scapula can move in six directions, each produced by specific primary muscles. The rhomboids (major and minor) function to stabilise the medial border of the scapula and are active in scapular adduction or retraction. The rhomboid minor originates from the spinous process of the seventh cervical and first thoracic vertebrae and inserts into the medial border of the scapula near the base of the scapular spine. The rhomboid major originates from the second through fifth thoracic vertebrae and inserts into the scapular border just below the insertion of the minor.
| Characteristics | Values |
|---|---|
| Common Name | Shoulder Blade |
| Description | A sturdy, flat, triangular bone that sits above the rib cage in the upper back |
| Function | It creates the shoulder joint where it meets with the head of the humerus (upper arm bone) |
| Movement | The scapula can move in six directions, including protraction, retraction, elevation, depression, upward rotation, and downward rotation |
| Muscles Attached | Latissimus Dorsi, Trapezius, Serratus Anterior, Pectoralis Minor, Teres Major, Levator Scapulae, Rhomboids, Deltoid, Biceps, Triceps, Coracobrachialis |
| Stabilizers | Serratus Anterior, Rhomboid Major and Minor, Levator Scapulae, Trapezius |
| Glenohumeral "Protectors" | Supraspinatus, Infraspinatus, Teres Minor, Subscapularis (also known as the Rotator Cuff Muscles) |
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What You'll Learn
The rhomboids (major and minor)
The rhomboids are two separate muscles: the rhomboid major and the rhomboid minor. These muscles lie deep beneath the trapezius to form parallel bands that extend from the vertebrae to the medial border of the scapula. The rhomboid minor is a cylindrical muscle that originates at the ligamentum nuchae and C7 and T1 vertebra, inserting at the scapula's medial border near the spine of the scapula. The rhomboid major, on the other hand, is a quadrangular muscle located inferior to the rhomboid minor. It originates from the spinous processes of the T2-T5 vertebra and inserts just below the rhomboid minor on the medial border of the scapula.
The rhomboid muscles play a crucial role in the movement and stabilization of the scapula. They work together with the serratus anterior, trapezius, and other muscles to anchor the scapula and prevent a condition known as "winging." Additionally, these muscles are responsible for retraction, elevation, and rotation of the scapula, as well as protraction of its medial border, ensuring its proper positioning at the posterior thoracic wall.
The motor function of the rhomboid muscles is controlled by the dorsal scapular nerve (DSN), which originates from the ventral ramus of the spinal nerve root C5. The rhomboid minor and major receive arterial blood supply from three sources: the dorsal scapular artery and the deep branch of the transverse cervical artery.
In certain individuals, a variation known as the rhomboid occipitalis can be observed. This thin muscle extends between the rhomboid minor and the occipital bone, adding to the complexity of the musculature in this region.
Overall, the rhomboids are essential for the proper functioning and stability of the scapula, contributing to the full range of motion required for the shoulder joint to operate effectively.
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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 ribs and inserts at the anterior surface of the scapula. The serratus anterior is one of the muscles responsible for rotational movements and stabilization of the scapula.
The main function of the serratus anterior is the anterolateral movement of the scapula. This movement involves rotating the scapula and lifting the arm above 90 degrees. Additionally, the serratus anterior is involved in protraction and upward rotation of the scapula, pulling the scapula forward and keeping it against the rib cage. This muscle is also important for scapular stabilization, ensuring that the shoulder blades remain against the rib cage during rest and movement.
The serratus anterior is a key muscle for athletes, particularly in sports that require repetitive motions such as swimming, tennis, or weightlifting. In athletic individuals, the serratus anterior may even be visible to the naked eye along the ribs underneath the axilla.
The innervation of the serratus anterior is supplied by the long thoracic nerve (C5-7), a branch of the brachial plexus. This nerve is crucial for the muscle's function, and damage to it can result in a functional loss of the serratus anterior. The vascular supply to the muscle comes from the superior and lateral thoracic arteries, as well as branches from the thoracodorsal artery.
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Pectoralis minor
The pectoralis minor is a muscle that originates from the margins of the third to fifth ribs, close to the costal cartilages. It is triangular in shape and is located under the pectoralis major, forming the anterior wall of the axilla. The pectoralis minor muscle is important in the stabilization of the scapula, pulling it downward and forward (protraction) against the thoracic wall. This muscle also depresses the point of the shoulder, drawing the scapula superiorly and throwing its inferior angle posteriorly.
The pectoralis minor is clinically significant and serves as a surgical landmark due to the underlying structures and its tendon. The nerves and blood supply to the upper limb pass deep to the pectoralis minor muscle, including the posterior, lateral, and medial cords of the brachial plexus. The medial pectoral nerve, a minor branch of the brachial plexus, provides the primary nerve supply to the pectoralis minor. Additionally, the lateral pectoral nerve contributes to the innervation of the pectoralis minor through the ansa pectoralis, resulting in innervation from the spinal roots of C5-T1.
The pectoralis minor also plays a role in dividing the axillary artery into three parts: medial, deep/posterior, and lateral, in relation to its medial, posterior, and lateral borders, respectively. This muscle is associated with various blood vessels, such as the thoracoacromial artery, superior thoracic artery, and lateral thoracic artery.
A shortened pectoralis minor can cause issues such as thoracic outlet syndrome and shoulder impingement. This can lead to pain, numbness, and tingling in the arm and hand. Additionally, trigger points in the pectoralis minor can result in referred pain patterns that start in the front of the shoulder and extend down the arm to the hand and fingers.
To address a tense or shortened pectoralis minor, specific exercises like the serratus punch and modified push-up plus can be implemented to activate the serratus anterior while minimising the activity of the pectoralis minor. These exercises help correct forward-rounded shoulders and alleviate associated symptoms.
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Latissimus dorsi
The latissimus dorsi is a large, flat muscle on the back that stretches to the sides, behind the arm. The name "latissimus dorsi" comes from Latin and means "broadest [muscle] of the back". The muscle is also commonly referred to as the "lats", especially among bodybuilders.
The latissimus dorsi is the widest muscle in the human body. It is relatively thin and covers almost all back muscles at the posterior trunk, except the trapezius. The muscle is attached to the scapula and can pull the inferior angle of the scapula in various directions, producing movements on the shoulder joint. These movements include internal rotation, adduction, and extension of the arm. The muscle also assists in depression of the arm with the teres major and pectoralis major.
The latissimus dorsi is innervated by the sixth, seventh, and eighth cervical nerves through the thoracodorsal (long subscapular) nerve. The muscle is supplied predominantly by the thoracodorsal artery, a continuation of the subscapular artery, which is a branch of the third part of the axillary artery. The latissimus dorsi also receives blood supply from the dorsal perforating branches of the inferior three posterior intercostal arteries and the superior three lumbar arteries.
The latissimus dorsi is closely related to the teres major, with the two muscles embryologically originating from the pre-muscle sheath of the arm. The latissimus dorsi and teres major also work together to extend the humerus, with extension and adduction being strongest when the motion is started from a position of partial flexion or abduction.
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Teres major
The teres major is a thick muscle of the shoulder joint. It originates from the posterior surface of the inferior angle of the scapula and the lower part of the lateral border of the scapula. It is covered by the teres minor and infraspinatus muscles on its posterior aspect, and by the subscapularis muscle on its anterior aspect. The teres major is one of the intrinsic muscles of the scapula, along with the subscapularis, teres minor, and infraspinatus. These muscles attach to the scapular surface and assist with movements of the glenohumeral joint.
The teres major muscle fibres run parallel to the fibres of the latissimus dorsi muscle. They converge onto a single tendon that inserts into the intertubercular sulcus (medial lip) of the humerus. The teres major is vascularized by the thoracodorsal branch of the subscapular artery and the posterior circumflex humeral artery. Its innervation is supplied by the lower subscapular nerve (C5-C7), a branch of the brachial plexus.
The main function of the teres major is to produce movements of the humerus at the glenohumeral joint. It pulls the anterior surface of the humerus medially towards the trunk (internal rotation) and can also extend the arm from a flexed position. Additionally, it contributes to the stabilization of the shoulder joint. When the humeral attachment is fixed, the teres major, along with the pectoralis major and latissimus dorsi muscles, can pull the trunk superiorly through adduction, which is why it is also referred to as the climbing muscle.
The teres major also works in synergy with the teres minor, latissimus dorsi, and pectoralis major to adduct the arm from the abducted position (lowering it). This function facilitates overhead upper limb movements such as pulling and throwing.
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Frequently asked questions
The rhomboids (major and minor) are responsible for stabilizing the medial border of the scapula and are active in scapular adduction or retraction.
The scapula, commonly known as the shoulder blade, is a flat, triangular-shaped bone that sits above the rib cage in the upper back.
Muscles attached to the scapula include the latissimus dorsi, teres major, pectoralis minor, coracobrachialis, and levator scapulae.
