Deltoid muscle

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Deltoid muscle
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Deltoid muscle
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Muscles connecting the upper extremity to the vertebral column
Origin and insertion of deltoid muscle Deltoid muscle origin and insertion.jpg
Origin and insertion of deltoid muscle
Details
Origin The anterior border and upper surface of the lateral third of the clavicle, acromion, spine of the scapula
Insertion Deltoid tuberosity of humerus
Artery Thoracoacromial artery, anterior and posterior humeral circumflex artery
Nerve Axillary nerve
Actions Shoulder abduction, flexion and extension
Antagonist Latissimus dorsi
Identifiers
Latin musculus deltoideus
MeSH D057645
TA98 A04.6.02.002
TA2 2452
FMA 32521
Anatomical terms of muscle

The deltoid muscle is the muscle [ citation needed ] 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 fibers, namely the

Contents

  1. anterior or clavicular part (pars clavicularis)
  2. posterior or scapular part (pars scapularis)
  3. intermediate or acromial part (pars acromialis)

The deltoid's fibres are Pennate muscle. However, electromyography suggests that it consists of at least seven groups that can be independently coordinated by the nervous system. [1]

It was previously called the deltoideus (plural deltoidei) and the name is still used by some anatomists. It is called so because it is in the shape of the Greek capital letter delta (Δ). Deltoid is also further shortened in slang as "delt".

A study of 30 shoulders revealed an average mass of 191.9 grams (6.77 oz) in humans, ranging from 84 grams (3.0 oz) to 366 grams (12.9 oz). [2]

Structure

Origin

  1. The anterior or clavicular fibers arise from most of the anterior border and upper surface of the lateral third of the clavicle. [3] The anterior origin lies adjacent to the lateral fibers of the pectoralis major muscle as do the end tendons of both muscles. These muscle fibers are closely related and only a small chiasmatic space, through which the cephalic vein passes, prevents the two muscles from forming a continuous muscle mass. [4]
  2. Intermediate or acromial fibers arise from the superior surface of the acromion process of the scapula. [3]
  3. Posterior or spinal fibers arise from the lower lip of the posterior border of the spine of the scapula. [3]
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Side.
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Front.
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Back.
Deltoid muscle animation4.gif
Animation.
Deltoid muscle.
  Anterior part of deltoid (arises from most of the anterior border and upper surface of the lateral third of the clavicle.)
  Intermediate part of deltoid (arises from the superior surface of the acromion process.)
  Posterior part of deltoid (arises from the lower lip of the posterior border of the spine of the scapula.)

Insertion

From this extensive origin the fibers converge toward their insertion on the deltoid tuberosity on the middle of the lateral aspect of the shaft of the humerus; the intermediate fibers passing vertically, the anterior obliquely backward and laterally, and the posterior obliquely forward and laterally.

Though traditionally described as a single insertion, 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. It additionally gives off extensions to the deep brachial fascia. Furthermore, the deltoid fascia contributes to the brachial fascia and is connected to the medial and lateral intermuscular septa. [5]

Blood supply

The deltoid is supplied by the thoracoacromial artery (acromial and deltoid branches), the circumflex humeral arteries, and the profunda brachii artery (deltoid branch). [6]

Nerve supply

The deltoid is innervated by the axillary nerve. [7] The axillary nerve originates from the anterior rami of the cervical nerves C5 and C6, via the superior trunk, posterior division of the superior trunk, and the posterior cord of the brachial plexus. [8]

Deltoid Muscle Labelled Deltoid Muscle.png
Deltoid Muscle Labelled

Studies have shown that there are seven neuromuscular segments to the deltoid muscle. Three of these lie in the anatomical anterior head of the deltoid, one in the anatomical middle head, and three in the anatomical posterior head of the deltoid. [9] These neuromuscular segments are supplied by smaller branches of the axillary nerve, and work in coordination with other muscles of the shoulder girdle include pectoralis major and supraspinatus. [9]

The axillary nerve is sometimes damaged during surgical procedures of the axilla, such as for breast cancer. It may also be injured by anterior dislocation of the head of the humerus. [10]

Structures under deltoid [11]

Function

Deltoid muscle with superior limb in abduction Deltoid muscle.JPG
Deltoid muscle with superior limb in abduction

When all its fibers contract simultaneously, the deltoid is the prime mover of arm abduction along the frontal plane. The arm must be medially rotated for the deltoid to have maximum effect. [12] This makes the deltoid an antagonist muscle of the pectoralis major and latissimus dorsi during arm adduction. The anterior fibers assist the pectoralis major to flex the shoulder. The anterior deltoid also works in tandem with the subscapularis, pecs and lats to internally (medially) rotate the humerus. The intermediate fibers perform basic shoulder abduction when the shoulder is internally rotated, and perform shoulder transverse abduction when the shoulder is externally rotated. They are not utilized significantly during strict transverse extension (shoulder internally rotated) such as in rowing movements, which use the posterior fibers. The posterior fibers assist the latissimus dorsi to extend the shoulder. Other transverse extensors, the infraspinatus and teres minor , also work in tandem with the posterior deltoid as external (lateral) rotators, antagonists to strong internal rotators like the pecs and lats.

An important function of the deltoid in humans is preventing the dislocation of the humeral head when a person carries heavy loads. The function of abduction also means that it would help keep carried objects a safer distance away from the thighs to avoid hitting them, as during a farmer's walk. It also ensures a precise and rapid movement of the glenohumeral joint needed for hand and arm manipulation. [2] The intermediate fibers are in the most efficient position to perform this role, though like basic abduction movements (such as lateral raise) it is assisted by simultaneous co-contraction of anterior/posterior fibers. [13]

The deltoid is responsible for elevating the arm in the scapular plane and its contraction in doing this also elevates the humeral head. To stop this compressing against the undersurface of the acromion the humeral head and injuring the supraspinatus tendon, there is a simultaneous contraction of some of the muscles of the rotator cuff: the infraspinatus and subscapularis primarily perform this role. In spite of this there may be still a 1–3 mm upward movement of the head of the humerus during the first 30° to 60° of arm elevation. [2]

Clinical significance

The most common abnormalities affecting the deltoid are tears, fatty atrophy, and enthesopathy. Deltoid muscle tears are unusual and frequently related to traumatic shoulder dislocation or massive rotator cuff tears. Muscle atrophy may result from various causes, including aging, disuse, denervation, muscular dystrophy, cachexia and iatrogenic injury. Deltoidal humeral enthesopathy is an exceedingly rare condition related to mechanical stress. Conversely, deltoideal acromial enthesopathy is likely a hallmark of seronegative spondylarthropathies and its detection should probably be followed by pertinent clinical and serological investigation. [14]

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.

Site of the intramuscular injection in deltoid: The intramuscular injections are commonly given in the lower half of the deltoid to avoid injury to the axillary nerve, which [15] winds around the surgical neck of the humerus.

Other animals

The deltoid is also found in members of the great ape family other than humans. The human deltoid is of similar proportionate size as the muscles of the rotator cuff in apes like the orangutan, which engage in brachiation and possess the muscle mass needed to support the body weight by the shoulders. In other apes, like the common chimpanzee, the deltoid is much larger than in humans, weighing an average of 383.3 gram compared to 191.9 gram in humans. This reflects the need to strengthen the shoulders, particularly the rotatory cuff, in knuckle walking apes for the purpose of supporting the entire body weight. [2]

The deltoid muscle is a main component of both the bat and pterosaur wing musculature, [16] but in crown-group birds it is strongly reduced, as they favour sternum attached muscles. Some Mesozoic flying theropods, however, had more developed deltoideus. [17]

Related Research Articles

<span class="mw-page-title-main">Scapula</span> Bone that connects the humerus (upper arm bone) with the clavicle (collar bone)

The scapula, also known as the shoulder blade, is the bone that connects the humerus with the clavicle. Like their connected bones, the scapulae are paired, with each scapula on either side of the body being roughly a mirror image of the other. The name derives from the Classical Latin word for trowel or small shovel, which it was thought to resemble.

<span class="mw-page-title-main">Humerus</span> Long bone of the upper arm

The humerus is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a rounded head, a narrow neck, and two short processes. The body is cylindrical in its upper portion, and more prismatic below. The lower extremity consists of 2 epicondyles, 2 processes, and 3 fossae. As well as its true anatomical neck, the constriction below the greater and lesser tubercles of the humerus is referred to as its surgical neck due to its tendency to fracture, thus often becoming the focus of surgeons.

<span class="mw-page-title-main">Rotator cuff</span> Group of muscles

The rotator cuff is a group of muscles and their tendons that act to stabilize the human shoulder and allow for its extensive range of motion. Of the seven scapulohumeral muscles, four make up the rotator cuff. The four muscles are:

<span class="mw-page-title-main">Axillary nerve</span> Nerve of the human body near the armpit

The axillary nerve or the circumflex nerve is a nerve of the human body, that originates from the brachial plexus at the level of the axilla (armpit) and carries nerve fibers from C5 and C6. The axillary nerve travels through the quadrangular space with the posterior circumflex humeral artery and vein to innervate the deltoid and teres minor.

<span class="mw-page-title-main">Shoulder</span> Part of the body

The human shoulder is made up of three bones: the clavicle (collarbone), the scapula, and the humerus as well as associated muscles, ligaments and tendons.

<span class="mw-page-title-main">Upper limb</span> Consists of the arm, forearm, and hand

The upper limbs or upper extremities are the forelimbs of an upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digits, including all the musculatures and ligaments involved with the shoulder, elbow, wrist and knuckle joints. In humans, each upper limb is divided into the shoulder, arm, elbow, forearm, wrist and hand, and is primarily used for climbing, lifting and manipulating objects. In anatomy, just as arm refers to the upper arm, leg refers to the lower leg.

<span class="mw-page-title-main">Pectoralis major</span> Main human chest muscle

The pectoralis major is a thick, fan-shaped or triangular convergent muscle of the human chest. It makes up the bulk of the chest muscles and lies under the breast. Beneath the pectoralis major is the pectoralis minor muscle.

<span class="mw-page-title-main">Teres minor muscle</span> Muscle of the rotator cuff

The teres minor is a narrow, elongated muscle of the rotator cuff. The muscle originates from the lateral border and adjacent posterior surface of the corresponding right or left scapula and inserts at both the greater tubercle of the humerus and the posterior surface of the joint capsule.

<span class="mw-page-title-main">Triceps</span> Muscle on the back of the upper arm

The triceps, or triceps brachii, is a large muscle on the back of the upper limb of many vertebrates. It consists of three parts: the medial, lateral, and long head. It is the muscle principally responsible for extension of the elbow joint.

<span class="mw-page-title-main">Suprascapular nerve</span> Mixed nerve of the upper limb

The suprascapular nerve is a mixed nerve that branches from the upper trunk of the brachial plexus. It is derived from the ventral rami of cervical nerves C5-C6. It provides motor innervation to the supraspinatus muscle, and the infraspinatus muscle.

<span class="mw-page-title-main">Supraspinatus muscle</span> Muscle of the upper back

The supraspinatus is a relatively small muscle of the upper back that runs from the supraspinous fossa superior portion of the scapula to the greater tubercle of the humerus. It is one of the four rotator cuff muscles and also abducts the arm at the shoulder. The spine of the scapula separates the supraspinatus muscle from the infraspinatus muscle, which originates below the spine.

<span class="mw-page-title-main">Infraspinatus muscle</span> Main external rotator of the shoulder

In human anatomy, the infraspinatus muscle is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa. As one of the four muscles of the rotator cuff, the main function of the infraspinatus is to externally rotate the humerus and stabilize the shoulder joint.

<span class="mw-page-title-main">Shoulder joint</span> Synovial ball and socket joint in the shoulder

The shoulder joint is structurally classified as a synovial ball-and-socket joint and functionally as a diarthrosis and multiaxial joint. It involves an articulation between the glenoid fossa of the scapula and the head of the humerus. Due to the very loose joint capsule ,that gives a limited interface of the humerus and scapula, it is the most mobile joint of the human body.

<span class="mw-page-title-main">Subscapularis muscle</span> Large triangle muscle of the shoulder

The subscapularis is a large triangular muscle which fills the subscapular fossa and inserts into the lesser tubercle of the humerus and the front of the capsule of the shoulder-joint.

<span class="mw-page-title-main">Teres major muscle</span> Muscle of the upper limb

The teres major muscle is a muscle of the upper limb. It attaches to the scapula and the humerus and is one of the seven scapulohumeral muscles. It is a thick but somewhat flattened muscle.

<span class="mw-page-title-main">Posterior humeral circumflex artery</span> Blood vessel

The posterior humeral circumflex artery arises from the third part of the axillary artery at the distal border of the subscapularis.

<span class="mw-page-title-main">Surgical neck of the humerus</span> Part of one of the bones of the arm

The surgical neck of the humerus is a bony constriction at the proximal end of shaft of humerus. It is situated distal to the greater tubercle and lesser tubercle, and proximal to the deltoid tuberosity.

<span class="mw-page-title-main">Quadrangular space</span>

The quadrangular space, also known as the quadrilateral space (of Velpeau) and the foramen humerotricipitale, is one of the three spaces in the axillary space. The other two spaces are: triangular space and triangular interval.

<span class="mw-page-title-main">Axillary space</span>

The axillary spaces are anatomic spaces. through which axillary contents leave the axilla. They consist of the quadrangular space, triangular space, and triangular interval. It is bounded by teres major, teres minor, medial border of the humerus, and long head of triceps brachii.

<span class="mw-page-title-main">Shoulder impingement syndrome</span> Medical condition

Shoulder impingement syndrome is a syndrome involving tendonitis of the rotator cuff muscles as they pass through the subacromial space, the passage beneath the acromion. It is particularly associated with tendonitis of the supraspinatus muscle. This can result in pain, weakness, and loss of movement at the shoulder.

References

  1. ↑ Brown, JM; Wickham, JB; McAndrew, DJ; Huang, XF (2007). "Muscles within muscles: Coordination of 19 muscle segments within three shoulder muscles during isometric motor tasks". J Electromyogr Kinesiol. 17 (1): 57–73. doi:10.1016/j.jelekin.2005.10.007. PMID   16458022.
  2. 1 2 3 4 Potau, JM; Bardina, X; Ciurana, N; Camprubí, D. Pastor JF; de Paz, F. Barbosa M. (2009). "Quantitative Analysis of the Deltoid and Rotator Cuff Muscles in Humans and Great Apes". Int J Primatol. 30 (5): 697–708. doi:10.1007/s10764-009-9368-8. S2CID   634575.
  3. 1 2 3 "Deltoid Muscle". Wheeless' Textbook of Orthopaedics. December 2011. Retrieved January 2012.
  4. ↑ Leijnse, J N A L; Han, S-H; Kwon, Y H (December 2008). "Morphology of deltoid origin and end tendons – a generic model". J Anat. 213 (6): 733–742. doi:10.1111/j.1469-7580.2008.01000.x. PMC   2666142 . PMID   19094189.
  5. ↑ Rispoli, Damian M.; Athwal, George S.; Sperling, John W.; Cofield, Robert H. (2009). "The anatomy of the deltoid insertion" (PDF). J Shoulder Elbow Surg. 18 (3): 386–390. doi:10.1016/j.jse.2008.10.012. PMID   19186076. Archived from the original (PDF) on 2012-09-04.
  6. ↑ Standring, S. (2005). Gray's Anatomy: The Anatomical Basis of Clinical Practice (39th ed.). Elsevier Churchill Livingstone.
  7. ↑ Anatomy photo:03:03-0103 at the SUNY Downstate Medical Center
  8. ↑ "Deltoid muscle". Kenhub. Retrieved 2019-09-21.
  9. 1 2 Brown, J M M; Wickham, J B; McAndrew, D J; Huang, X F (2007). "Muscles within muscles: Coordination of 19 muscle segments within three shoulder muscles during isometric motor tasks". Journal of Electromyography and Kinesiology. 17 (1): 57–73. doi:10.1016/j.jelekin.2005.10.007. PMID   16458022.
  10. ↑ Avis, Duncan; Power, Dominic (2018-03-26). "Axillary nerve injury associated with glenohumeral dislocation". EFORT Open Reviews. 3 (3): 70–77. doi:10.1302/2058-5241.3.170003. ISSN   2058-5241. PMC   5890131 . PMID   29657847.
  11. ↑ Chaurasia, Bhagwan Din BD (2023). Chaurasia's Human Anatomy (9th ed.). New Delhi: CBS publisher (published 1979–2023). pp. 3–4. ISBN   9789354664762.
  12. ↑ Radiography of the Upper Extremities: 24 ARRT Category A. CE4RT, 2014. 201. Print.
  13. ↑ "Lateral Deltoid Raise - Shoulder Exercise & Workout | MG". Archived from the original on 2012-06-25. Retrieved 2013-06-17.
  14. ↑ Arend CF. Ultrasound of the Shoulder. Master Medical Books, 2013. Chapter on deltoideal enthesopathy available at ShoulderUS.com
  15. ↑ Rajput, Vishram singh (15 July 2014). Anatomy (2nd ed.). Thomson Press India Ltd., Faridabad, Haryana: Reed Elsevier India Private Limited. p. 65. ISBN   978-81-312-3729-8.
  16. ↑ Witton, Mark (2013). Pterosaurs: Natural History, Evolution, Anatomy. Princeton University Press. ISBN   978-0691150611.
  17. ↑ Voeten, Dennis F.A.E.; et al. (2018). ""(13 March 2018). "Wing bone geometry reveals active flight in Archaeopteryx". Nature Communications. 9 (1): 923. doi: 10.1038/s41467-018-03296-8 . PMC   5849612 . PMID   29535376.
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