Logan Steele
The scapula, or shoulder blade, is the bone that sits above the rib cage in the upper back. It is capable of six directions of movement, each produced by specific primary muscles. The muscles that rotate the scapula include the upper and lower trapezius, the serratus anterior, the levator scapulae, the teres major, the rhomboids major and minor, the subscapularis, the infraspinatus, the supraspinatus, the deltoid, the latissimus dorsi, the pectoralis major, and the coracobrachialis.
| Characteristics | Values |
|---|---|
| Muscles attached to the scapula | Deltoid, Latissimus Dorsi, Trapezius, Serratus Anterior, Biceps Brachii, Coracobrachialis, Pectoralis Minor, Triceps, Levator Scapulae, Teres Major, Rhomboids Major and Minor, Subscapularis, Infraspinatus, Supraspinatus, Teres Minor |
| Muscles that rotate the scapula | Serratus Anterior, Upper and Lower Trapezius |
| Serratus Anterior muscle weakness test | Therapist applies a downwards resisting force against the scapular plane abduction of the shoulder at about 120–130° and against upward rotation of the scapula |
| Serratus Anterior muscle weakness test results | Failure to resist the force, resulting in the shoulder breaking into adduction and the scapula's inability to rotate upwards |
| Serratus Anterior muscle pain causes | Tension, stress, overuse, Serratus Anterior Myofascial Pain Syndrome (SAMPS) |
| Serratus Anterior muscle pain results | Impaired scapular protraction and upward rotation, reduced scapular/shoulder stability, increased risk of injury to the rotator cuff and shoulder girdle |
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What You'll Learn
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 muscle fibres follow the course of the ribs onto which they attach. The serratus anterior muscle is further divided into three parts: the superior part, the intermediate part, and the inferior part. The superior part originates from the first to the second rib and inserts at the superior angle of the scapula. The intermediate part originates from the second to the third rib and inserts at the medial border of the scapula. The inferior part originates from the fourth to the eighth or ninth rib and inserts at the medial border and inferior angle of the scapula.
The contraction of the entire 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 arm to lift above 90 degrees. Conversely, the superior part depresses the scapula and acts antagonistically. The serratus anterior is also responsible for the active stabilisation of the scapula within the shoulder. When the scapula is fixed, the muscle lifts the ribs and acts as an accessory inspiratory muscle.
The innervation of the serratus anterior is supplied by the long thoracic nerve (C5-7), a branch of the brachial plexus. The vascular supply to the muscle comes from the superior and lateral thoracic arteries (branches of the axillary artery) and branches from the thoracodorsal artery (a branch of the subscapular artery).
The serratus anterior is a key scapular stabiliser, keeping the shoulder blades against the ribcage at rest and during movement. It is the prime mover in scapular protraction and scapular upward rotation. When the serratus anterior is inhibited, scapular protraction and scapular upward rotation are impaired, limiting the overhead range of motion and reducing overall scapular/shoulder stability. This can increase the risk of injury to the rotator cuff and shoulder girdle.
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Trapezius muscle
The trapezius muscle is a large, paired muscle in the upper back, extending from the occipital bone to the lower thoracic vertebrae of the spine and laterally to the spine of the scapula. The muscle is named for its shape, which resembles a trapezium or diamond-shaped quadrilateral. Each side of the body has one trapezius muscle, which together form a trapezoid shape with four sides, two of which are parallel. These muscles are essential for maintaining posture and moving the upper back, neck, and head.
The trapezius muscle has three sections: upper, middle, and lower. The upper section connects to the skull and neck (cervical spine), while the middle and lower sections attach to bones in the thoracic spine. The trapezius muscle also connects to the scapula (shoulder blade) and collarbone (clavicle). The upper fibres of the trapezius elevate the scapulae, while the middle fibres retract the scapulae and the lower fibres depress the scapulae. In addition, the trapezius induces scapular rotation, with the upper and lower fibres rotating the scapula around the sternoclavicular articulation.
The trapezius muscle works in conjunction with other muscles to produce coordinated movements, particularly those involving the scapula. For example, the rhomboids major and minor work with the trapezius to retract and stabilise the scapula, playing a key role in shoulder movement and posture. The levator scapulae elevates the scapula and works with the upper trapezius to lift and rotate the shoulder. The serratus anterior works with the lower trapezius to rotate the scapula upward during arm elevation, allowing the arm to lift smoothly above shoulder height.
The trapezius muscle is crucial for movements such as pushing, reaching forward, or pulling down, as it helps maintain scapular stability. It also assists in abduction of the shoulder above 90 degrees by rotating the glenoid upward. Dysfunction of the trapezius can result in winged scapula or scapular dyskinesia, characterised by abnormal mobility or function of the scapula.
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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, an acronym that references the first letter of the names of the four muscles: 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 movements while maintaining the stability of the glenohumeral joint. They provide the "fine-tuning" movements of the head of the humerus within the glenoid fossa, keeping the head of the humerus within the small glenoid fossa of the scapula to enlarge the range of motion in the GH joint and avoid mechanical obstruction.
The supraspinatus muscle is the only muscle of the rotator cuff that is not a rotator of the humerus. The infraspinatus is a powerful lateral rotator of the humerus and facilitates external rotation, or the rotation of the arm outward at the shoulder. The subscapularis is the largest muscle of the rotator cuff and facilitates internal rotation of the arm at the shoulder. The teres minor is adjacent to and below the infraspinatus and, like that muscle, helps with external rotation. It is much smaller and becomes more active toward the end of a rotation or when the arm is in certain positions, such as when it is raised at a significant angle away from the body.
The rotator cuff muscles are essential players in almost every type of shoulder movement. Balanced strength and flexibility in each of the four muscles are vital to maintain functioning of the entire shoulder girdle. A rotator cuff tear is a common injury that can occur at any age and is the most common upper extremity condition seen by primary and sports medicine doctors and orthopedic surgeons. It can occur due to trauma or repetitive strain, with tears classified based on their size and muscle atrophy.
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Rhomboids major and minor
The scapula, or shoulder blade, is a bone in the upper back that sits above the rib cage. It is capable of six directions of movement, each produced by specific primary muscles. The rhomboids major and minor are two such muscles that attach to the scapula.
The rhomboid major is an extrinsic muscle of the shoulder, located deep to the trapezius and inferior to the rhomboid minor. It originates from the spinous processes of T2-T5 vertebrae and attaches to the medial border of the scapula, between the scapula spine and inferior angle. The rhomboid major is responsible for retracting and rotating the scapula.
The rhomboid minor is a thin, flat muscle located in the upper back, between the scapula and the spine. It is positioned superior to the rhomboid major and attaches to the medial border of the scapula. The rhomboid minor works in conjunction with the rhomboid major to produce scapular movement.
Together, the rhomboids major and minor play a crucial role in scapular stability and movement. They contribute to the upward rotation, posterior tilt, and external rotation of the scapula during arm elevation. This complex movement, known as the scapulohumeral rhythm, involves the coordination of the scapula, clavicle, and humerus to achieve the full range of arm motion.
By understanding the anatomy and functions of the rhomboids major and minor, we can appreciate their importance in maintaining shoulder stability and facilitating the dynamic movements of the scapula.
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Levator scapulae
The levator scapulae is a posterior axio-appenducular muscle that connects the upper limb to the vertebral column. It is located in the posterior triangle of the neck and originates on the posterior tubercle of the transverse process of cervical vertebrae 1 to 4. The levator scapulae inserts onto the vertebral margin of the scapula, between the superior angle and the root of the spine.
The levator scapulae is innervated by the cervical nerve (C3-C4) and the dorsal scapular nerve (C5), and it receives its blood supply from the dorsal scapular artery. This muscle is responsible for elevating the scapula and rotating it downward, as well as tilting the glenoid cavity inferiorly. When the scapula is fixed, contraction of the levator scapulae leads to lateral flexion of the cervical vertebral column, providing stability during rotation.
The levator scapulae is associated with several clinical conditions. Levator scapulae syndrome, for example, is characterised by tenderness over the upper medial angle of the scapula, and it often goes undiagnosed. Treatment options for this condition include physical therapy and local corticosteroid injections. Additionally, trigger points are common in this muscle and can cause pain or discomfort, which can be relieved through various active movements and modalities.
The length and tension of the levator scapulae can be assessed by placing a patient in a supine position, stabilising the ipsilateral scapula, and then performing a side bend and head rotation. The muscle's function and integrity are crucial in maintaining proper scapulohumeral coordination and stability.
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Frequently asked questions
The muscles that rotate the scapula include the upper and lower trapezius, the serratus anterior, the levator scapulae, the teres major and minor, the rhomboids major and minor, the subscapularis, the infraspinatus, and the supraspinatus.
The serratus anterior is a key scapular stabiliser, keeping the shoulder blades against the rib cage at rest and during movement. It is also responsible for scapular protraction and upward rotation.
The trapezius muscle influences the movements of the scapula and helps the shoulder with adduction and flexion in the initial degrees of movement.
A weak serratus anterior can lead to scapular winging, impaired scapular protraction, and reduced scapular upward rotation, limiting the overhead range of motion and decreasing overall shoulder stability.
