Logan Steele
The scapula is a sturdy, flat, triangular bone that sits just behind the shoulders. It is a key part of the shoulder joint and acts as an anchor for many of the arm, upper back, and shoulder muscles. The scapula permits a range of motion for the shoulder, including protraction, retraction, elevation, depression, and rotation. The scapula is also important for completing daily movements, such as raising your arms over your head or brushing your teeth. The stability of the scapula depends on the coordinated activity of the surrounding musculature, with the main stabilizers being the serratus anterior, rhomboid major and minor, levator scapulae, and trapezius muscles.
| Characteristics | Values |
|---|---|
| Main stabilizers | Serratus anterior, rhomboid major and minor, levator scapulae, and trapezii |
| Glenohumeral "protectors" | Supraspinatus, infraspinatus, teres minor, and subscapularis |
| Intrinsic muscles | Rotator cuff muscles, teres major, subscapularis, teres minor, and infraspinatus |
| Extrinsic muscles | Triceps, biceps, and deltoid |
| Third group of muscles | Levator scapulae, trapezius, rhomboids, and serratus anterior |
| Protraction | Serratus anterior, pectoralis major, and pectoralis minor muscles |
| Retraction | Trapezius, rhomboids, and latissimus dorsi muscles |
| Elevation | Trapezius, levator scapulae, and rhomboid muscles |
| Depression | Latissimus dorsi, serratus anterior, pectoralis major and minor, and the trapezius muscles |
| Upward rotation | Trapezius and serratus anterior muscles |
| Downward rotation | Latissimus dorsi, levator scapulae, rhomboids, and the pectoralis major and minor muscles |
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The Serratus Anterior
The vascular supply to the serratus anterior comes from the superior and lateral thoracic arteries (branches of the axillary artery) and branches from the thoracodorsal artery (branch of subscapular artery). The innervation of the serratus anterior is supplied by the long thoracic nerve (C5-7), a branch of the brachial plexus.
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Rhomboid Major and Minor
The rhomboid muscles are a group of two muscles: the rhomboid major and the rhomboid minor. They are located in the upper back, stretching from the top of the spine (at the base of the neck) to the scapula (shoulder blade). The rhomboid major is an extrinsic muscle of the shoulder, located deep to the trapezius muscle and inferior to the rhomboid minor. It 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 rhomboid muscles are responsible for several important functions, including scapular retraction and downward rotation. They assist in lifting the shoulder blade and play a crucial role in stabilizing the scapula during arm elevation. By acting eccentrically, the rhomboid muscles control the position of the scapula as the arm moves up and down, countering the lateral translation force of the serratus anterior muscle. This ensures smooth and synchronous movement of the shoulder complex.
The rhomboid muscles receive innervation from the dorsal scapular nerve (C5). Their blood supply comes from the dorsal scapular artery and the dorsal branches of the posterior intercostal arteries. These muscles are essential for maintaining the stability and mobility of the shoulder joint, allowing for a full range of motion during activities such as reaching and lifting.
Injuries to the rhomboid muscles can occur, and one sign of their dysfunction is pain in the upper back or shoulder region. In some cases, injury to the dorsal scapular nerve can cause paralysis of the rhomboid muscles, affecting the positioning and movement of the scapula. It is important to maintain proper shoulder muscle health through rest, stretching, and strengthening exercises to prevent injuries and ensure optimal function of the rhomboid muscles and the scapula.
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Levator Scapulae
The levator scapulae is a long, slender muscle that belongs to the extrinsic muscles of the back. It is a thin, strap-like skeletal muscle that originates from the transverse processes of the first four cervical vertebrae (C1-C4) and inserts at the superior angle and medial border of the scapula, between the superior angle and base of the spine of the scapula. The upper third of the levator scapulae lies beneath the sternocleidomastoid muscle, while its lower third is covered by the trapezius muscle.
The main function of the levator scapulae is to elevate and retract the shoulder girdle at the scapulothoracic joint. It also helps prevent depression of the girdle when carrying heavy loads. Additionally, the muscle is involved in the stabilization of the scapula and the inferior rotation of the glenoid cavity. When the scapula is fixed, contraction of the levator scapulae leads to the lateral flexion of the cervical vertebral column, providing stability during rotation.
The actions of the levator scapulae are complemented by other muscles, including the trapezius, latissimus dorsi, rhomboids, pectoralis major, and pectoralis minor. These muscles work together to achieve protraction, retraction, elevation, depression, upward rotation, and downward rotation of the scapula, allowing for full-functional upper extremity movement and contributing to the stability of the shoulder joint.
The levator scapulae can be susceptible to tightness and trigger points due to forward head posture, which can cause cervicogenic headaches. Assessing and treating levator scapulae length and tension are important in relieving associated pain and discomfort.
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Trapezius
The trapezius is a large, triangular, broad, and thin muscle that covers the upper back, shoulders, and neck. It is made up of two big muscles, with three sections—upper, middle, and lower—that run from the base of the neck down to the middle of the back. The trapezius muscles are also referred to as "traps" or "trap muscles".
The trapezius muscles are paired and shaped like trapeziums or diamond-shaped quadrilaterals. They extend longitudinally from the occipital bone to the lower thoracic vertebrae of the spine and laterally to the spine of the scapula. The upper fibres of the trapezius originate from the back of the head and proceed downward and laterally to be inserted into the posterior border of the lateral third of the clavicle. The middle fibres arise from the back of the neck and the spinous processes of the first, second, and third thoracic vertebrae. They are inserted into the medial margin of the acromion and into the superior lip of the posterior border of the spine of the scapula. The lower fibres of the trapezius arise from the spinous processes of the remaining thoracic vertebrae and proceed upward and laterally to converge near the scapula.
The trapezius muscles help maintain and adjust posture, allowing and supporting the spinal column to remain erect when a person is standing. They are also used for active movements such as side bending, rotation of the head, elevating and depressing the shoulders, and internally rotating the arm. The trapezius muscles are involved in retraction, elevation, and depression of the scapula. The upper fibres of the trapezius elevate and upwardly rotate the scapula and extend the neck. The middle fibres adduct (medially retract) the scapula, and the lower fibres depress and aid the upper fibres in upwardly rotating the scapula. The descending muscle fibres of the trapezius internally rotate the arms, while the transverse muscle fibres retract the scapulae, and the ascending muscle fibres medially rotate the scapulae.
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Rotator Cuff
The rotator cuff is a group of four muscles and tendons that surround the shoulder joint and hold the bones together. The four muscles are the supraspinatus, subscapularis, infraspinatus, and teres minor. These muscles originate from the scapula (shoulder blade) and connect to the head of the humerus (upper arm bone), forming a cuff at the shoulder joint. This allows the rotator cuff to keep the shoulder and upper arm stable during movement.
The rotator cuff muscles have several functions, including abduction, internal rotation, and external rotation of the shoulder. They also control the fine-tuning movements of the shoulder. For example, the supraspinatus allows for rotation and lifting of the arm, while the subscapularis lets you hold your arm outstretched away from your body. The infraspinatus and subscapularis are particularly important for scapular plane shoulder abduction, generating forces that are two to three times greater than the supraspinatus muscle. However, the supraspinatus is more effective for general shoulder abduction due to its moment arm. The teres minor helps with turning and rotating the arm.
The rotator cuff is essential for the stability and mobility of the shoulder, which is the most flexible joint in the human body. It compresses the glenohumeral joint during abduction of the arm, allowing the deltoid muscle to elevate the arm. Without the rotator cuff, the humeral head would ride up partially out of the glenoid fossa, reducing the efficiency of the deltoid muscle.
Injuries to the rotator cuff are common, especially among athletes who play contact sports. Symptoms of a rotator cuff injury include shoulder pain, arm weakness, and difficulty moving the shoulder without pain. Treatment for a rotator cuff injury typically involves immobilizing the shoulder joint in a sling for 4 to 6 weeks, followed by passive exercises to improve stability, strength, and range of motion.
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Frequently asked questions
The main muscles that stabilize the scapula are the serratus anterior, rhomboid major and minor, levator scapulae, and trapezius.
The scapula is a sturdy, flat, triangular bone that serves as part of the shoulder joint and as an anchor for many of the arm, upper back, and shoulder muscles.
Some scapular stabilization exercises include:
- Driving through both hands evenly, pushing the sternum away from the wall until both scapulas open up and your upper back is slightly rounded.
- Holding a long band with both hands, palms facing each other, and pulling the band apart with both arms as wide as possible.
- Facing a flat wall and holding a medicine ball in front of you, then pressing the medicine ball against the wall.
The intrinsic muscles of the scapula include the rotator cuff muscles, teres major, subscapularis, teres minor, and infraspinatus.
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