Maximus Gage
The deltoid muscle is a large, triangular-shaped muscle that lies over the shoulder joints. It is the main muscle of the shoulder and is responsible for a wide range of movements at the shoulder joint. The muscle consists of three groups of fibres, which further subdivide the muscle into three parts: the anterior, or clavicular, part; the posterior, or scapular, part; and the lateral/intermediate, or acromial, part. Each part has its own function and contributes to the overall movement and stability of the shoulder joints and upper arm.
| Characteristics | Values |
|---|---|
| Shape | Triangular |
| Location | Uppermost portion of the arm and at the tip of the shoulder |
| Parts | Anterior, or clavicular; Posterior, or scapular; Lateral/Intermediate, or acromial |
| Function | Shoulder abduction, flexion, medial rotation, horizontal flexion, elevation, extension, internal rotation, external rotation, and stability of the shoulder joint |
| Blood supply | Thoracoacromial branch of the axillary artery |
| Secondary blood supply | Posterior circumflex artery |
| Innervation | Axillary nerve |
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What You'll Learn
Deltoid muscle shape
The deltoid muscle is triangular in shape, with the base of the triangle located on top of the shoulder. The muscle fibres wrap around the top part of the humerus (upper arm bone), with the top of the triangle found at the deltoid tuberosity, a bony ridge on the upper part of the humerus that serves as the insertion point for the muscle.
The deltoid muscle is named after the Greek letter delta, which is shaped like an equilateral triangle. It is a large, oval-shaped muscle positioned on the uppermost portion of the arm and at the tip of the shoulder, providing a round contour to the shoulders. The deltoid muscle is the main muscle of the shoulder and is responsible for a wide range of movements at the shoulder joint.
The deltoid muscle consists of three groups of fibres, which subdivide the muscle into three parts: the anterior, or clavicular, part; the posterior, or scapular, part; and the lateral/intermediate, or acromial, part. Each part has its own origin point, but all three parts insert onto the same location, the deltoid tuberosity of the humerus.
The anterior deltoid, or front delts, is located on the front portion of the shoulder and upper arm region, with its origin on the anterior surface of the clavicle (collarbone). The lateral deltoid, or middle delts, is located directly atop the shoulder, with its origin on the acromion process of the scapula (shoulder blade). The acromion process is a bony projection that can be felt on the top portion of the scapula. The posterior deltoid, or rear delt, is located on the back part of the shoulder and upper arm region, with its origin on the spine of the scapula, a bony ridge located on the upper part of the shoulder blade.
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Deltoid muscle location
The deltoid muscle is a large, triangular-shaped muscle that lies over the shoulder joints, or glenohumeral joints, and traverses from the spine of the scapula to the lateral portion of the clavicle. It is the main muscle of the shoulder and is positioned on the uppermost portion of the arm and at the tip of the shoulder, providing a round contour to the shoulders. The base, or widest part, of the triangle is located on top of the shoulder, with the muscle fibres wrapping around the top part of the humerus, or upper arm bone. The top of the triangle is found at the deltoid tuberosity, a bony ridge on the upper part of the humerus that serves as the insertion point for this muscle.
The deltoid muscle consists of three groups of fibres, which subdivide the muscle into three parts: the anterior, or clavicular, part; the posterior, or scapular, part; and the lateral/intermediate, or acromial, part. Each part has its own point of origin but all three parts of the muscle insert onto the same location, the deltoid tuberosity. The origin for the anterior head is the anterior surface of the clavicle, or collarbone, with the muscle then inserting onto the deltoid tuberosity of the humerus. The second part of the deltoid, the lateral deltoid, is located directly atop the shoulder, with its origin found on the acromion process of the scapula, a bony projection that can be felt on the top portion of the scapula, or shoulder blade. The insertion point for the lateral delts is the deltoid tuberosity of the humerus. The posterior deltoid muscle, also known as the scapular or rear delt, is the third portion of the deltoid and is located on the rear, or back, part of the shoulder and upper arm region. Its origin is the spine of the scapula, a bony ridge located on the upper part of the shoulder blade, and it inserts onto the deltoid tuberosity of the upper humerus.
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Deltoid muscle blood supply
The deltoid muscle is a large, thick, triangular shoulder muscle, named for its resemblance to the Greek letter 'delta' (Δ). Due to its size, the deltoid muscle receives a rich vascular supply from various sources.
The deltoid muscle receives blood from the thoracoacromial branch of the axillary artery. The thoracoacromial artery gives rise to two collaterals that supply the anterior part of the deltoid muscle: the deltoid artery and the acromial artery. The deltoid artery gives off a superior collateral branch that runs under the clavicle. The acromial artery runs deep to the anterior part of the deltoid muscle, near the clavicle and the acromion.
The deltoid muscle also receives minor contributions from the posterior circumflex humeral artery, which supplies the posterior and middle parts of the deltoid, and the profunda brachii artery, a branch of the brachial artery. The profunda brachii artery is the only artery supplying the deltoid that is not a branch of the axillary artery.
The deltoid muscle is innervated by the axillary nerve, which arises from the anterior rami of the cervical nerves C5 and C6. The axillary nerve supplies the deltoid muscle with seven neuromuscular segments, three in the anterior head, one in the middle head, and three in the posterior head.
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Deltoid muscle innervation
The deltoid muscle is a thick, triangular shoulder muscle, resembling the inverted Greek letter delta in shape. It is a key player in shoulder stability and motion, and its function must be accurately tested to determine muscular or nervous injury.
The deltoid muscle is innervated by the axillary nerve, which arises from C5 and C6 roots and is a terminal branch of the brachial plexus. The axillary nerve has three possible distribution patterns:
- A single branch to the teres minor, an anterior branch to the clavicular and acromial deltoid, and a posterior branch to the spinal deltoid.
- An anterior branch to the posterior two-thirds of the deltoid and a posterior branch to the teres minor.
- An anterior branch to the acromial and clavicular deltoid and a posterior branch to the spinal deltoid.
The deltoid muscle can also be innervated by the lateral pectoral nerve, as observed in 86.2% of cases in one study. This nerve passes over the axillary artery and perforates the clavipectoral fascia, following the thoracoacromial vessels. The lateral pectoral nerve has two topographical patterns:
- A proximal variant, where the nerve enters the pectoral region under the clavicle.
- A distal variant, where the nerve enters the pectoral region from the axillary fossa around the caudal border of the pectoralis minor.
Additionally, according to Bergman's encyclopedia of anatomical variations, the deltoid muscle can be innervated by the medial pectoral nerve. The detailed topography of the lateral pectoral nerve for innervating the deltoid has not been well defined in the literature.
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Deltoid muscle movement
The deltoid muscle is a large, triangular-shaped muscle that lies over the shoulder joints, giving the shoulders their round contour. It is the main muscle of the shoulder and is responsible for a wide range of arm movements at the shoulder joint.
The deltoid muscle is composed of three groups of fibres, which further subdivide the muscle into three parts: the anterior, or clavicular, part; the posterior, or scapular, part; and the lateral/intermediate, or acromial, part. Each part has its own origin point, but all three parts insert onto the same location.
The anterior deltoid, or front delts, is located on the front portion of the shoulder and upper arm region. Its origin is the anterior surface of the clavicle, or collarbone, and it inserts onto the deltoid tuberosity of the humerus (upper arm bone). In isolation from the other fibres of the muscle, this part of the deltoid flexes, medially rotates, and horizontally flexes the upper arm at the shoulder joint.
The lateral deltoid, also known as the intermediate or middle delts, is located directly atop the shoulder. Its origin is the acromion process of the scapula, which is a bony projection that can be felt on the top portion of the shoulder blade. The insertion point for the lateral delts is the same as for the anterior deltoid: the deltoid tuberosity of the humerus.
The posterior deltoid, or rear delts, is the third portion of the deltoid muscle. It is located on the rear, or back, part of the shoulder and upper arm region. The origin of this muscle is the spine of the scapula, a bony ridge located on the upper part of the shoulder blade. The posterior deltoid inserts onto the deltoid tuberosity of the upper humerus, just like the other two parts of the deltoid muscle.
Together, the three parts of the deltoid muscle work to produce abduction of the shoulder joint, which occurs when the arm is lifted to the side. The deltoid muscle also assists in the elevation of the arm during glenohumeral elevation and plays a vital role in the movement and stability of the shoulder joints and upper arm.
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Frequently asked questions
The deltoid muscle is the main muscle of the shoulder. It is a large, triangular-shaped muscle that wraps around the upper arm bone.
The deltoid muscle is responsible for the abduction of the arm at the shoulder joint. It also assists in the elevation of the arm during a process called glenohumeral elevation. The deltoid muscle helps move your upper arm and stabilizes the shoulder joint.
The deltoid muscle consists of three groups of fibres, which subdivide the muscle into three parts: the anterior, or clavicular part; the posterior, or scapular part; and the lateral/intermediate, or acromial part.
