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The scapula, or shoulder blade, is a flat, triangular bone that sits above the rib cage in the upper back. It has a large surface area, allowing a significant number of muscles to attach to it. The protraction and retraction of the scapula happen around a vertical axis passing through the lateral end of the clavicle. The scapula can move in six directions, and each movement is produced by specific primary muscles. The muscles that protract the scapula include the serratus anterior, the pectoralis minor, and the rhomboid minor.
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What You'll Learn
Serratus Anterior Muscle
The Serratus Anterior Muscle, also known as the ""big swing muscle" or the "boxer's muscle", is a key muscle in the human body. It 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. Its main part lies deep under the scapula and the pectoral muscles. It is easily palpable and may even be visible to the naked eye in athletic bodies along the ribs underneath the axilla.
The serratus anterior muscle is divided into three parts according to their points of insertion: the serratus anterior superior, the serratus anterior intermediate, and the serratus anterior inferior. The superior part is inserted near the superior angle, the intermediate part along the medial border, and the inferior part near the inferior angle of the scapula. The inferior part is the most prominent and powerful of the three. The serratus anterior is innervated by the long thoracic nerve, a branch of the brachial plexus.
The serratus anterior muscle has several important functions. Firstly, it is the prime mover in scapular protraction, pulling the scapula forward and around the rib cage. This movement is essential for the anteversion of the arm and is particularly noticeable when someone throws a punch. Secondly, it assists in scapular upward rotation, working in conjunction with the upper and lower fibres of the trapezius muscle to enable overhead lifting. Thirdly, it actively stabilises the scapula within the shoulder, keeping the shoulder blades against the rib cage during rest and movement. Finally, when the scapula is fixed, the serratus anterior acts as an accessory inspiratory muscle, lifting the ribs and supporting breathing.
Weakness of the serratus anterior muscle can lead to altered line of pull of the rotator cuff muscle, increasing the risk of subacromial impingement syndrome. It can also result in scapular winging, where the scapula tilts in a medial, "wing-like" position. Common causes of serratus anterior muscle weakness include tension, stress, and overuse, particularly in sports with repetitive motions such as swimming, tennis, or weightlifting.
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Pectoralis Minor Muscle
The pectoralis minor muscle is a thin, triangular muscle located at the anterior aspect of the chest, beneath the pectoralis major muscle. It is one of the most superficial muscles in this region and is part of the anterior axioappendicular (thoracoappendicular) muscles, along with the pectoralis major, subclavius, and serratus anterior muscles. The pectoralis minor muscle plays a significant role in the movement of the scapula, particularly in protraction, and it works in conjunction with the serratus anterior muscle to achieve a full range of motion for the scapula.
Originating from the anterior surface of the 3rd, 4th, and 5th ribs, near the costal cartilages, the pectoralis minor muscle inserts into the medial border and upper surface of the coracoid process of the scapula. This muscle is responsible for protracting and depressing the scapula, which involves pulling the scapula forward and down. This action is crucial for reaching the arm forward. Additionally, the pectoralis minor muscle aids in respiration by elevating the ribs during deep inspiration when the pectoral girdle is fixed or elevated.
The pectoralis minor muscle also has clinical importance and serves as a surgical landmark due to its proximity to vital structures. Beneath the pectoralis minor lie the nerves and blood supply to the upper limb, including the brachial plexus and its posterior, lateral, and medial cords. The muscle is innervated by the medial pectoral nerve (C8, T1), a minor branch of the brachial plexus arising from the cervical spinal cord. The lateral pectoral nerve may also contribute to its innervation through a communicating branch called the 'ansa pectoralis'.
In terms of vascular supply, the pectoralis minor receives blood from several arteries, including the thoracoacromial artery, superior thoracic artery, and lateral thoracic artery. These arteries are branches of the axillary artery, which the pectoralis minor divides into three parts: the first part medial to the medial border of the muscle, the second part deep or posterior to it, and the third part lateral to the lateral border. This muscle is associated with the axillary nodes, which are classified based on their positions relative to it.
A tense or shortened pectoralis minor muscle can result in pain and discomfort. It can entrap nerves in the armpit region, causing pain, numbness, and tingling sensations down the arm and into the hand. Additionally, a shortened pectoralis minor can restrict the movement of the shoulder joint by limiting scapular rotation. Therefore, maintaining proper muscle health and flexibility is crucial to avoid such issues.
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Levator Scapulae Muscle
The levator scapulae is a long and slender muscle that is a part of the group of superficial extrinsic muscles of the back. It is a posterior axio-appenducular muscle that connects the upper limb to the vertebral column and is located in the posterior triangle of the neck. 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 superior third of the levator scapulae lies deep to the sternocleidomastoid, while the inferior third is deep to the trapezius muscle. The levator scapulae is innervated by the anterior rami of spinal nerves C3 and C4, as well as the dorsal scapular nerve (C5), a branch of the brachial plexus. The dorsal scapular artery is the predominant blood supply to the levator scapulae muscle.
The main function of the levator scapulae muscle is to elevate and retract the shoulder girdle at the scapulothoracic joint. It also helps prevent the depression of the girdle when carrying heavy loads. Additionally, the levator scapulae muscle contributes to the stabilisation 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 to the same side and helps stabilise the vertebral column during rotation. Bilateral contraction of the levator scapulae helps in the extension of the cervical spine.
The levator scapulae muscle can be palpated, and its length and tension can be assessed by placing the patient in a supine position, stabilising the ipsilateral scapula, and performing a contralateral side bend and head rotation. Trigger points are common in this muscle and can be palpated for in both the superior and inferior attachments. Pain or discomfort caused by the levator scapulae can be relieved by various modalities and active movements.
The levator scapulae muscle is not commonly involved in surgical procedures. However, it is implicated in the Eden-Lange procedure, which aims to recreate the functionality lost in trapezius muscle palsy, also known as "winged scapula". In this procedure, the tendon of the levator scapulae is transferred to the acromion. The Modified Eden-Lange procedure is a variation that involves transferring the rhomboid minor to the supraspinatus fossa and attaching the rhomboid major to the infraspinatus fossa, with the levator scapulae then attached to the spine of the scapula.
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Rhomboid Minor Muscle
The rhomboid minor is a small skeletal muscle in the upper back that connects the scapula to the vertebrae of the spinal column. It is one of the muscles that form the shoulder girdle, helping to keep the shoulder blade and shoulder stable. The scapula, or shoulder blade, is the bone that sits above the rib cage in the upper back, creating the shoulder joint where it meets the head of the humerus (upper arm bone).
The rhomboid minor arises from the nuchal ligament and the 7th cervical and 1st thoracic vertebrae, inserting onto the medial border of the scapula. It is innervated by the dorsal scapular nerve, a branch of the brachial plexus, and receives its arterial blood supply from the dorsal scapular artery. The muscle fibres travel inferolaterally, inserting onto the portion of the medial border of the scapula adjacent to the spine of the scapula.
The rhomboid minor acts together with the rhomboid major muscle. When the trapezius muscle is contracted, the rhomboid minor and major retract the scapula. They also work together to elevate the medial border of the scapula medially and upward, rotating the scapulae downward in synergy with the levator scapulae muscle. The rhomboid minor and major thus contribute to arm movement, enabling a person to lift their arm above their head.
The rhomboid minor can be located by holding the hand on the posterior aspect of the hip and pushing the elbow backward against resistance, during which the muscle can be palpated. Pain in the rhomboid muscles may feel like tenderness around the shoulder blade and can be caused by repetitive motions, overstretching, or sitting for an extended period. Gentle exercises, pain relief medications, anti-inflammatory drugs, and hot and cold therapy can help ease rhomboid muscle pain.
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Rhomboid Major Muscle
The rhomboid major is a skeletal muscle of the back that connects the scapula with the vertebrae of the spinal column. It is a quadrangular or diamond-shaped muscle located inferior to the rhomboid minor. The rhomboid major is considered a superficial back muscle and is deep to the trapezius. The trapezius has evolved separately, but the rhomboid major and other muscles in this group evolved from the first eight or ten ribs and the transverse processes of the cervical vertebrae.
The rhomboid major muscle originates from the spinous processes of the thoracic vertebrae T2–T5 and the supraspinous ligament. It inserts onto the lower portion of the medial border of the scapula, from about the level of the scapular spine to the scapula's inferior angle. The rhomboid major, along with the rhomboid minor, keeps the scapula pressed against the thoracic wall and retracts the scapula towards the vertebral column. This helps to hold the scapula and the upper limb onto the ribcage. The rhomboid major also works with the levator scapulae to elevate and retract the scapula, and with the serratus anterior to anchor the scapula and prevent winging.
The rhomboid major is innervated by the dorsal scapular nerve, which originates from the ventral ramus of the spinal nerve root C5. The dorsal scapular nerve provides innervation to the levator scapulae and serratus posterior superior muscles before innervating the rhomboid major and minor at their anterior border. The rhomboid major and minor muscles also derive their arterial blood supply from the dorsal scapular artery.
The implications of scapular instability caused by the rhomboid major include scapular winging during scapular protraction, excessive lateral rotation, and depression of the scapula. Treatment for scapular instability may include surgery followed by physical therapy or occupational therapy. Physical therapy may include stretching and endurance exercises for the shoulder, with Pilates and yoga also suggested as potential treatments.
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Frequently asked questions
The muscles that protract the scapula are the serratus anterior, pectoralis minor, and the lowermost fibres of the serratus anterior muscle.
The scapula, commonly referred to as the shoulder blade, is a flat, triangular bone that sits above the rib cage in the upper back.
There are 17 muscles attached to the scapula due to its large surface area, keeping it fixed to the thoracic wall and allowing movement.
Some examples of muscles attached to the scapula include the supraspinatus muscle, deltoid muscle, triceps brachii muscle, infraspinatus muscle, and teres major muscle.
The function of the scapulothoracic joint is to enable and integrate the movements of the scapula against the underlying chest wall with the movements of the upper limb.
