Dominic Stone
The deltoid muscle is the muscle forming the rounded contour of the human shoulder. It is a thick, triangular shoulder muscle, getting its name from its shape, which resembles the Greek letter 'delta' (Δ). The deltoid is a multipennate muscle, with multiple rows of diagonal fibres converging on a central tendon. The muscle fibres then run inferiorly towards the humeral shaft and converge to form a short tendon that inserts at the deltoid tuberosity on the lateral aspect of the humerus. The deltoid is the prime mover of arm abduction along the frontal plane.
| Characteristics | Values |
|---|---|
| Muscle type | Multipennate muscle |
| Muscle shape | Triangular |
| Muscle function | Shoulder abduction, flexion, and internal rotation |
| Muscle origin | Clavicle, acromion, and spine of scapula |
| Muscle insertion | Humerus |
| Muscle innervation | Axillary nerve |
| Muscle blood supply | Thoracoacromial artery, circumflex humeral arteries, and profunda brachii artery |
| Muscle coverage | Rotator cuff muscles, pectoralis major, tendon of pectoralis minor, coracobrachialis, biceps brachii, triceps brachii, coracoacromial ligament, subacromial bursa, bony structures, and neurovascular structures |
| Muscle segments | Seven neuromuscular segments |
| Muscle parts | Three parts: anterior, middle, and posterior |
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What You'll Learn
The deltoid muscle is a multipennate muscle
The deltoid muscle is a thick, triangular shoulder muscle that gets its name from its shape, which resembles the Greek letter 'delta' (Δ). It is a large muscle with a wide origin, spanning the clavicle, acromion, and spine of the scapula. It passes inferiorly, surrounding the glenohumeral joint on all sides, and inserts onto the humerus.
The deltoid muscle has three functionally and anatomically distinct parts: the acromial part (also known as the middle or central part), and the clavicular and scapular spinal parts. The acromial part is the largest and strongest part of the deltoid muscle, and it is a multipennate muscle. It arises as four intramuscular septa, which interdigitate with the three tendons at the insertion site (one each for the anterior, posterior, and middle parts). The four septa are connected by short, strong muscle fibres.
The clavicular (anterior) and scapular spinal (posterior) parts of the deltoid muscle are unipennate and converge directly onto the inserting tendon. The deltoid muscle as a whole can be considered a multipennate muscle due to the structure of its middle part. The middle part of the deltoid muscle contains four deep fibrous bands that glide inside half-cone-shaped distal fibrous structures, which merge into the distal tendon of the deltoid muscle. This multipennate structure favours strength over the range of motion of the muscle.
The deltoid muscle is responsible for elevating the arm in the scapular plane, and its contraction elevates the humeral head. It is the principal abductor of the arm at the glenohumeral joint, although it requires assistance from the supraspinatus muscle for initial abduction. The deltoid also plays a significant role in stabilization during arm abduction, along with the rotator cuff muscles.
The deltoid muscle is innervated by the axillary nerve (C5, C6), a branch of the brachial plexus. It receives a rich vascular supply from various sources, including the thoracoacromial artery, the circumflex humeral arteries, and the profunda brachii artery. The deltoid muscle is a superficial muscle, lying deep only to its overlying fascia, the platysma muscle, and skin. This makes it easily observable and palpable.
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It has three distinct parts
The deltoid muscle is the muscle forming the rounded contour of the human shoulder. It is also known as the 'common shoulder muscle'. The deltoid is a thick, triangular shoulder muscle. It gets its name from its shape, which resembles the Greek letter ‘delta’ (Δ). The muscle has a wide origin, spanning the clavicle, acromion, and spine of the scapula. It then passes inferiorly, surrounding the glenohumeral joint on all sides, and inserts onto the humerus.
The deltoid has three functionally and anatomically distinct parts. These are the acromial part (sometimes known as the middle or central part), and the clavicular (anterior) and scapular spinal (posterior) parts. The acromial part is the largest and strongest of the three, and is a multipennate muscle. It arises as four intramuscular septa, which interdigitate with the three tendons at the insertion site (one each for the anterior, posterior, and middle parts). The four septa are connected by short, strong muscle fibres. The clavicular and scapular spinal parts are both unipennate and converge directly onto the inserting tendon.
The three parts of the deltoid each have a different origin. The clavicular (anterior) part originates from the superior surface and the anterior border of the lateral third of the clavicle. The acromial part (middle fibres) abducts the arm, while the clavicular and scapular spinal parts play a significant role in stabilization, ensuring a steady plane of abduction. The clavicular part (anterior fibres) can also act as a flexor and internal rotator of the arm, while the scapular spinal part (posterior fibres) can extend and externally rotate the arm.
The deltoid is a superficial muscle of the shoulder, lying deep only to its overlying fascia, the platysma muscle, and skin. Due to its superficial nature, the deltoid can be easily observed and palpated. It overlies a number of other muscular structures, including the rotator cuff muscles, the pectoralis major, and the tendon of pectoralis minor, as well as tendons of coracobrachialis, both heads of biceps brachii, and long and lateral heads of the triceps brachii muscle. The deltoid also covers the coracoacromial ligament, subacromial bursa, and bony structures, as well as neurovascular structures.
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The muscle is responsible for arm abduction
The deltoid muscle is the muscle forming the rounded contour of the human shoulder. It is also known as the 'common shoulder muscle', particularly in other animals such as the domestic cat. Anatomically, the deltoid muscle is made up of three distinct sets of muscle fibres, namely the anterior or clavicular part (commonly known as the front delt), the posterior or scapular part (commonly known as the rear delt), and the intermediate or acromial part (commonly known as the side delt). The deltoid muscle is the principal abductor of the arm at the glenohumeral joint. The acromial part (middle fibres) abducts the arm, while the clavicular and scapular spinal parts play a significant role in stabilization, ensuring a steady plane of abduction.
The deltoid muscle is responsible for arm abduction, which means raising your arm out to the side of your body. It also compensates for lost arm strength in the case of an injury, such as a rotator cuff tear. The deltoid muscle is the prime mover of arm abduction along the frontal plane when all its fibres contract simultaneously. The arm must be medially rotated for the deltoid to have maximum effect. This makes the deltoid an antagonist muscle of the pectoralis major and latissimus dorsi during arm adduction. The deltoid muscle is also responsible for flexion (moving your arm forward, towards an overhead position) and extension (moving your arm backward, behind your body).
The deltoid muscle is a thick, triangular shoulder muscle. It gets its name from its shape, which is similar to the Greek letter 'delta' (Δ). The muscle has a wide origin, spanning the clavicle, acromion, and spine of the scapula. It passes inferiorly, surrounding the glenohumeral joint on all sides, and inserts onto the humerus. The deltoid is a multipennate muscle, with four intramuscular septa that interdigitate with the three tendons at the insertion site. The four septa are connected by short, strong muscle fibres. The deltoid muscle has a very broad origin and a narrow base, thus creating its triangular shape. The deltoid is a superficial muscle, lying close to the surface of the skin. This makes it easily observable and palpable.
The deltoid muscle is tested by asking the patient to abduct the arm against resistance applied with one hand, and feeling for the contracting muscle with the other hand. To properly test the function of the deltoid and the axillary nerve, the arm must be beyond 15 degrees of abduction. Once the arm is in this position, the patient then pushes against resistance. If the muscle is functioning properly, contraction of the muscle should be felt near the acromion of the scapula.
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The deltoid is the prime mover of arm abduction
The deltoid muscle is a large, thick, triangular-shaped muscle that forms the rounded contour of the human shoulder. It is also known as the 'common shoulder muscle' and is considered the primary mover in the movement of the arm away from the body, which is known as abduction. This action occurs primarily when the arm is lifted sideways, away from the body. The deltoid is a very powerful muscle and is used in many everyday activities, such as putting clothes on a line, carrying shopping bags, and washing hair, as well as athletic activities like netball, swimming, and water polo.
The deltoid has three functionally and anatomically distinct parts: the anterior or clavicular part (commonly known as the front delt), the posterior or scapular part (commonly known as the rear delt), and the intermediate or acromial part (commonly known as the side delt). The acromial part, or the middle fibres, is the largest and strongest part of the deltoid muscle. It abducts the arm, while the clavicular and scapular spinal parts play a significant role in stabilization, ensuring a steady plane of abduction. The deltoid's fibres are pennate muscle, and electromyography suggests that it consists of at least seven groups that can be independently coordinated by the nervous system.
The deltoid has a very broad origin and a narrow base, creating its triangular shape. It has a wide origin spanning the clavicle, acromion, and spine of the scapula. It passes inferiorly, surrounding the glenohumeral joint on all sides, and inserts onto the humerus. The deltoid is formed of acromial, clavicular, and scapular spinal parts. The deltoid insertion is divided into two or three discernible areas corresponding to the muscle's three areas of origin. The insertion is an arch-like structure with strong anterior and posterior fascial connections flanking an intervening tissue bridge.
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The muscle is susceptible to injury and atrophy
The deltoid is a large, thick, triangular shoulder muscle that is responsible for elevating the arm in the scapular plane. It is a powerful muscle that is used in many everyday activities and athletic endeavours. Due to its role and location, the deltoid is susceptible to injury and atrophy.
The deltoid is formed of acromial, clavicular, and scapular spinal parts, and it is a multipennate muscle. The acromial part, or the middle fibres, abducts the arm, while the clavicular and scapular spinal parts play a significant role in stabilization. The clavicular part can act as a flexor and internal rotator of the arm, while the scapular spinal part can extend and externally rotate the arm. The deltoid muscle fibres converge to a narrow, strong tendon and insert into the deltoid tuberosity located approximately halfway down the lateral aspect of the shaft of the humerus.
The deltoid muscle is impacted by common injuries and clinical procedures. Its function can be reduced or compromised by axillary nerve injury, rupture of the deltoid itself, or iatrogenic damage to the muscle. The axillary nerve may be injured by shoulder fracture or dislocation, and this can lead to atrophy of the deltoid muscle. The deltoid muscle has an intimate relationship with the axillary nerve and neighbouring rotator cuff muscles, and injury to these structures may be masked by compensating deltoid strength.
The most common abnormalities affecting the deltoid are tears, fatty atrophy, and enthesopathy. Deltoid muscle tears are often related to traumatic shoulder dislocation or massive rotator cuff tears. Muscle atrophy may result from various causes, including ageing, disuse, denervation, muscular dystrophy, cachexia, and iatrogenic injury.
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Frequently asked questions
The deltoid muscle is the muscle forming the rounded contour of the human shoulder. It is also known as the 'common shoulder muscle'.
When a muscle has a widespread expansion over a sizable area and the fascicles come to a single, common attachment point, it is called a convergent muscle. The attachment point could be a tendon, an aponeurosis, or a raphe.
Yes, the deltoid is a multipennate muscle with fascicles that insert into multiple tendons, converging towards a common tendon.
The deltoid is responsible for elevating the arm in the scapular plane. It is the prime mover of arm abduction along the frontal plane when all its fibres contract simultaneously.
The deltoid is made up of three distinct sets of muscle fibres: the anterior or clavicular part (front delt), the posterior or scapular part (rear delt), and the intermediate or acromial part (side delt).
