Dominic Stone
The deltoid muscle is a large, thick, triangular-shaped shoulder muscle that gives the shoulder its rounded contour. It is composed of three parts: the anterior or clavicular part, the intermediate or acromial part, and the posterior or scapular spinal part. The deltoid muscle is a key shoulder stabilizer and helps with arm movement. It is a superficial muscle, lying deep only to its overlying fascia, the platysma muscle, and skin.
| Characteristics | Values |
|---|---|
| Shape | Thick and triangular |
| Name origin | Named after the Greek letter 'delta' due to its shape |
| Parts | Anterior or clavicular, middle or acromial, and posterior or spinal |
| Function | Shoulder abduction and stabilisation |
| Muscle type | Skeletal |
| Common issues | Adhesive capsulitis, axillary nerve palsy, bursitis, deltoid fibrosis, rotator cuff tears, shoulder impingement syndrome, shoulder separation, strains and overuse injuries, tendonitis |
| Blood supply | Thoracoacromial branch of the axillary artery |
| Nerve supply | Axillary nerve |
| Arterial supply | Thoracoacromial artery (acromial and deltoid branches), circumflex humeral arteries, and the profunda brachii artery (deltoid branch) |
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What You'll Learn
The deltoid is a large, thick, triangular shoulder muscle
The deltoid is composed of three distinct portions: the anterior or clavicular part (front delt), the intermediate or acromial part (middle or central, and also known as the side delt), and the posterior or scapular part (rear delt). The acromial part is the largest and strongest of the three. The deltoid has a very broad origin and a narrow base, creating its triangular shape. The muscle has a wide origin, spanning the clavicle, acromion, and spine of the scapula, and passes inferiorly, surrounding the glenohumeral joint on all sides.
The deltoid is a key shoulder stabilizer, giving the shoulder its rounded contour. It is involved in multiple actions, including abduction of the arm at the glenohumeral joint when the acromial part contracts individually, flexion and medial rotation of the arm when the clavicular part contracts individually, and extension and lateral rotation of the arm when the scapular spine part contracts individually. The deltoid is the prime mover of arm abduction along the frontal plane when all its fibres contract simultaneously. It also assists in forward elevation.
The deltoid is a common site for intramuscular injections, including vaccinations. It is susceptible to various conditions, such as adhesive capsulitis (frozen shoulder), axillary nerve palsy, bursitis, and deltoid fibrosis. Deltoid pain can occur in individuals who perform repetitive overhead activities, such as house painters, swimmers, and pitchers.
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It is a common site for intramuscular injections
The deltoid muscle is a large, thick, triangular shoulder muscle. It gets its name from its shape, which resembles the inverted Greek letter 'delta' (Δ). The deltoid is a common site for intramuscular injections, including vaccinations. This is because it is easy for clinicians to administer injections at this site and for patients to expose it. It is also the most commonly used site for vaccines worldwide.
Intramuscular injections are a common practice in modern medicine. They are used to deliver drugs and vaccines. Intramuscular injections are often used when other types of delivery methods are not recommended. For example, some drugs are irritating to veins, or a suitable vein cannot be located. In other cases, drugs may be destroyed by the digestive system when swallowed.
The deltoid muscle is a preferred site for intramuscular injections because of its easy accessibility. It is a superficial muscle, meaning it lies deep only to its overlying fascia, the platysma muscle, and skin. Its superficial nature makes it easy to observe and palpate. The deltoid is also a key shoulder stabilizer, preventing inferior glenohumeral joint displacement while the arm is completely adducted and bearing a heavy load.
However, it is important to note that there is a lack of uniform guidelines and algorithms for administering intramuscular injections in the deltoid muscle. As a result, there is a risk of injury to the underlying vessels and nerves. To avoid this, healthcare professionals should be properly trained and educated on the proper injection technique, and patients should be instructed on how to expose the injection site. Safe injection techniques include washing hands with soap and warm water, using a needle that is long enough to reach the muscle without penetrating the nerves and blood vessels underneath, and applying light pressure to the injection site with a piece of gauze.
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It is the principal abductor of the shoulder
The deltoid muscle is a thick, triangular shoulder muscle that gets its name from its shape, which resembles the inverted Greek letter delta (Δ). It is a common site for intramuscular injections, including vaccinations. The deltoid is the principal abductor of the shoulder, allowing for arm abduction or raising your arm to the side of your body. It also assists in flexion and extension of the arm, as well as stabilization of the shoulder joint.
The deltoid muscle has three functionally and anatomically distinct parts: the acromial (or intermediate), clavicular (or anterior), and scapular spinal (or posterior) parts. The acromial part, located in the middle, is the largest and strongest section of the deltoid muscle. It abducts the arm, allowing movement to the front, side, and back. The clavicular and scapular spinal parts play a crucial role in stabilization, ensuring a steady plane of abduction. Additionally, the clavicular part can act as a flexor and internal rotator of the arm, while the scapular spinal part assists in extending and externally rotating the arm.
The deltoid muscle originates from the scapular spine, superior acromial surface, and lateral third of the clavicle. It has a broad origin and a narrow base, creating its distinctive triangular shape. The deltoid muscle distally attaches to the deltoid tuberosity of the humerus. When the three parts of the deltoid contract simultaneously, they assist in abducting the arm past 15 degrees. The deltoid cannot initiate abduction independently but works alongside other shoulder muscles like the rotator cuff muscles to enable a full range of motion.
The deltoid muscle is a key shoulder stabilizer, preventing inferior glenohumeral joint displacement during activities like deadlifts. It also compensates for weak shoulder abduction due to rotator cuff tears. The deltoid receives its blood supply from the thoracoacromial branch of the axillary artery and is innervated by the axillary nerve, a branch of the brachial plexus. Deltoid muscle pain can occur in individuals who perform repetitive overhead arm movements, such as swimmers or pitchers.
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The deltoid covers several other muscular structures
The deltoid muscle is a large, thick, triangular shoulder muscle. It gets its name from its shape, which resembles the Greek letter 'delta' (Δ). The deltoid is a key shoulder stabilizer, helping to move the arm in different directions. It also protects and stabilizes the shoulder joint. The deltoid covers several other muscular structures, including:
- Rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis)
- Pectoralis major and the tendon of pectoralis minor
- Tendons of coracobrachialis, both heads of biceps brachii, and long and lateral heads of the triceps brachii muscle
- Coracoacromial ligament
- Subacromial bursa
- Bony structures (coracoid process and proximal humerus)
- Neurovascular structures (the axillary nerve and anterior and posterior circumflex humeral vessels) of the shoulder region
The deltoid is a common site for intramuscular injections, including vaccinations. It is also susceptible to various conditions and injuries, such as adhesive capsulitis (frozen shoulder), axillary nerve palsy, bursitis, and deltoid fibrosis.
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It is a key shoulder stabiliser
The deltoid is a large, thick, triangular-shaped shoulder muscle. It is a key shoulder stabiliser and is responsible for abducting the arm in the scapular plane. The deltoid is formed of three distinct sections: the acromial, clavicular and scapular spinal parts. The clavicular and scapular spinal parts play a significant role in stabilisation, ensuring a steady plane of abduction. The deltoid also compensates for weak shoulder abduction due to rotator cuff tears.
The deltoid muscle is superficial in nature, meaning it lies deep only to its overlying fascia, the platysma muscle and skin. Its superficial nature means it can be easily palpated. The deltoid covers 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 muscle gets its name from its shape, which resembles the Greek letter 'delta' (Δ). It has a wide origin, spanning the clavicle, acromion and spine of the scapula, and passes inferiorly, surrounding the glenohumeral joint on all sides. The deltoid is the principal abductor of the shoulder and is a very powerful muscle, used in many everyday activities and athletic pursuits.
The deltoid is the prime mover of arm abduction along the frontal plane. When the three parts of the deltoid contract simultaneously, the muscle can assist in abducting the arm past 15°. The anterior and posterior parts of the deltoid stabilise the arm, while the lateral segment assists in raising the arm from 15° to 100° degrees. The deltoid also works with the pectoralis major to flex the arm when walking.
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Frequently asked questions
The deltoid muscle is a large, thick, triangular shoulder muscle. It is the muscle that forms the rounded contour of the human shoulder.
The deltoid muscle helps you lift your arm to the front, side and back, and move it in different directions. It is also a key shoulder stabilizer.
The deltoid muscle gets its name from its shape, which resembles the Greek letter 'delta' (Δ).
The deltoid muscle is superficial to the glenohumeral (shoulder) joint. It is also superficial to the proximal tendons of the biceps brachii and triceps brachii muscles, and the axillary nerve.
