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'{{Redirect|Delts|the fraternity|Delta Tau Delta}} {{Infobox muscle | Name = Deltoid muscle | Latin = musculus deltoideus | Image = Deltoideus.png | Caption = Deltoid muscle | Image2 = 1119 Muscles that Move the Humerus b.png | Caption2 = Muscles connecting the upper extremity to the vertebral column | Origin = the anterior border and upper surface of the lateral third of the [[clavicle]], [[acromion]], [[Spine of scapula|spine]] of the [[scapula]] | Insertion = [[deltoid tuberosity]] of [[humerus]] | Blood = [[thoracoacromial artery]], [[anterior humeral circumflex artery|anterior]] and [[posterior humeral circumflex artery]] | Nerve = [[Axillary nerve]] | Action = [[shoulder]] [[Abduction (kinesiology)|abduction]], [[flexion]] and [[Extension (kinesiology)|extension]] | Antagonist = [[Latissimus dorsi]] }} 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, it appears to be made up of three distinct sets of fibers though [[electromyography]] suggests that it consists of at least seven groups that can be independently coordinated by the [[nervous system]].<ref>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. {{PMID|16458022}} {{doi|10.1016/j.jelekin.2005.10.007}}</ref> 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 alphabet|Greek]] capital letter [[Delta (letter)|delta]] (Δ). Deltoid is also further shortened in [[slang]] as "'''delt'''". A study of 30 shoulders revealed an average mass of {{convert|191.9|g}} in humans, ranging from {{convert|84|g}} to {{convert|366|g}}.<ref name="Potau">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 30:697–708. {{DOI|10.1007/s10764-009-9368-8}}</ref> ==Structure== Previous studies showed that the insertion of the intramuscular tendons of the deltoid muscle formed three discrete sets of [[muscle fiber]]s, often referred to as "heads":<ref>[http://www.fitstep.com/Advanced/Anatomy/Shoulders.htm The Anatomy of the Shoulder Muscles]: "The Deltoid is a three-headed muscle that caps the shoulder. The three heads of the Deltoid are the Anterior, Lateral, and Posterior."</ref> # The [[anterior]] or clavicular fibers arise from most of the anterior border and upper surface of the lateral third of the clavicle.<ref name="Wheeless">{{Cite web | title = Deltoid Muscle | publisher = Wheeless' Textbook of Orthopaedics | url = http://www.wheelessonline.com/ortho/deltoid_muscle | date = December 2011 | accessdate = January 2012 }}</ref> 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.<ref name="Leijnse-etal">{{Cite journal | title = Morphology of deltoid origin and end tendons&nbsp;– a generic model | last1 = Leijnse | first1 = J N A L | last2 = Han | first2 = S-H | last3 = Kwon | first3 = Y H | journal = J Anat |date=December 2008 | volume = 213 | issue = 6 | pages = 733–742 | doi = 10.1111/j.1469-7580.2008.01000.x | pmc= 2666142 | pmid=19094189 }}</ref> #*The '''anterior deltoids'''<ref>[http://www.exrx.net/Muscles/DeltoidAnterior.html Anterior Deltoid]</ref> are commonly called '''front delts'''<ref name="MaF">[http://www.muscleandfitness.com/training/arms/pick-your-delts Pick up your delts] from [[Muscle and Fitness]]: "target point: front/middle delts"</ref> for short. # Lateral or acromial fibers arise from the superior surface of the [[acromion]] process of the [[scapula]].<ref name="Wheeless" /> #*They are commonly called '''lateral deltoid'''.<ref name="ExLat">[http://www.exrx.net/Muscles/DeltoidLateral.html Lateral deltoid]</ref> This muscle is also called '''middle delts''',<ref name="MaF" /> '''outer delts''',<ref>[http://www.livestrong.com/article/530154-the-best-exercise-for-outer-delts/ The Best Exercise for Outer Delts] on LiveStrong.com in 2011</ref> or '''side delts'''<ref name="ExLat" /> for short. #*They are also mistakenly called '''medial deltoid''',<ref>[http://www.abcbodybuilding.com/anatomy/shouldersanatomy1.htm Shoulders Anatomy] {{Webarchive|url=https://web.archive.org/web/20120428203909/http://www.abcbodybuilding.com/anatomy/shouldersanatomy1.htm |date=2012-04-28 }} by Yu Yevon</ref> which is wrong, as their origin is the least medial portion of the deltoid. # Posterior or spinal fibers arise from the lower lip of the [[Posterior (anatomy)|posterior]] border of the [[spine of the scapula]].<ref name="Wheeless" /> #*They are commonly called '''posterior deltoid'''<ref>[http://www.exrx.net/Muscles/DeltoidPosterior.html Posterior Deltoid]</ref> or '''rear deltoid'''<ref>[http://www.exrx.net/Stretches/DeltoidPosterior/RearDelt.html Rear Deltoid Stretch]</ref> ('''rear delts''' for short<ref>[http://www.leehayward.com/rear_delts.htm Lee Hayward - Rear delts]</ref>). Fick<ref>{{Cite book | last = Fick | first = R. | title = Handbuch der Anatomie und Mekanik der Gelenke | location = Jena | publisher = Gustav Fischer | year = 1911 }}</ref> divided these three groups of fibers, often referred to as parts (Latin: ''pars'') or bands, into seven functional components as did Kapandji and Sakoma Y et al. :<ref name="Kapandji-60">{{cite book | last = Kapandji | first = Ibrahim Adalbert | title = The Physiology of the Joints: Volume One Upper Limb | publisher = Churchill Livingstone | location = New York | year = 1982 | edition = 5th }}</ref><ref>[Anatomical and functional segments of the deltoid muscle. J Anat. 2011 Feb;218(2):185-90. doi: 10.1111/j.1469-7580.2010.01325.x. Epub 2010 Nov 30. ]: "</ref> the anterior part has two components (I and II); the lateral one (III); and the posterior four (IV, V, VI, and VII) components. In [[standard anatomical position]] (with the upper limb hanging alongside the body), the central components (II, III, and IV) lie lateral to the axis of abduction and therefore contribute to abduction from the start of the movement while the other components (I, V, VI, and VII) then act as adductors. During abduction most of these latter components (except VI and VII which always act as adductors) are displaced laterally and progressively start to abduct.<ref name="Kapandji-60" /> {{multiple image | footer = Deltoid muscle.{{Legend|red|Anterior part of deltoid (arises from most of the anterior border and upper surface of the lateral third of the [[clavicle]].)}}{{Legend|LawnGreen |Lateral part of deltoid (arises from the superior surface of the [[acromion]] process.)}}{{Legend|blue|Posterior part of deltoid (arises from the lower lip of the posterior border of the spine of the scapula.)}} | align = left | image1 = Deltoid muscle top10.png | width1 = 200 | alt1 = Side | caption1 = Side. | image2 = Deltoid muscle top8.png | width2 = 200 | alt2 = Front | caption2 = Front. | image3 = Deltoid muscle top9.png | width3 = 200 | alt3 = Back | caption3 = Back. | image4 = Deltoid muscle animation4.gif | width4 = 200 | alt4 = Animation | caption4 = Animation. }}{{Clear}} ===Insertion=== From this extensive origin the fibers converge toward their insertion on the [[deltoid tuberosity]] on the middle of the [[Human anatomical terms#Anatomical directions|lateral]] aspect of the shaft of the [[humerus]]; the middle fibers passing vertically, the anterior obliquely backward and laterally, and the posterior obliquely forward and laterally. Though traditionally described as a single fucking 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 [[Brachial fascia|deep brachial fascia]]. Furthermore, the [[deltoid fascia]] contributes to the brachial fascia and is connected to the [[Medial intermuscular septum of arm|medial]] and [[Lateral intermuscular septum of arm|lateral intermuscular septa]]. <ref>{{Cite journal |last1=Rispoli |first1=Damian M. |last2=Athwal |first2=George S. |last3=Sperling |first3=John W. |last4=Cofield |first4=Robert H. |title=The anatomy of the deltoid insertion |journal=J Shoulder Elbow Surg |year=2009 |volume=18 |issue=3 |pages=386–390 |url=http://www.anatomytrains.com/uploads/rich_media/Rispoli2009_anatomyDeltoidInsertion.pdf |doi=10.1016/j.jse.2008.10.012 |pmid=19186076 |url-status=dead |archiveurl=https://web.archive.org/web/20120904122301/http://www.anatomytrains.com/uploads/rich_media/Rispoli2009_anatomyDeltoidInsertion.pdf |archivedate=2012-09-04 }}</ref> ===Blood supply=== The deltoid is supplied by the [[posterior circumflex humeral artery]] and the deltoid branch of the [[thoracoacromial artery]] which branches from the [[axillary artery]].<ref name="Sunny" /> ===Nerve supply=== The deltoid is innervated by the [[axillary nerve]].<ref name="Sunny">{{SUNYAnatomyLabs|03|03|01|03}}</ref> The axillary nerve originates from the [[anterior ramus of spinal nerve|anterior rami]] of the [[spinal nerves|cervical nerves]] C5 and C6, via the superior trunk, posterior division of the superior trunk, and the posterior cord of the brachial plexus.<ref>{{Cite web|url=https://www.kenhub.com/en/library/anatomy/the-deltoid-muscle|title=Deltoid muscle|website=Kenhub|language=en|access-date=2019-09-21}}</ref> 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.<ref>{{cite journal |last1=Brown |first1=J M M |last2=Wickham |first2=J B |last3=McAndrew |first3=D J |last4=Huang |first4=X F |title=Muscles within muscles: Coordination of 19 muscle segments within three shoulder muscles during isometric motor tasks |journal=Journal of Electromyography and Kinesiology |date=2007 |volume=17 |issue=1 |pages=57–73 |doi=10.1016/j.jelekin.2005.10.007 |pmid=16458022 }}</ref> 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.<ref>{{cite journal |last1=Brown |first1=J M M |last2=Wickham |first2=J B |last3=McAndrew |first3=D J |last4=Huang |first4=X F |title=Muscles within muscles: Coordination of 19 muscle segments within three shoulder muscles during isometric motor tasks |journal=Journal of Electromyography and Kinesiology |date=2007 |volume=17 |issue=1 |pages=57–73 |doi=10.1016/j.jelekin.2005.10.007 |pmid=16458022 }}</ref> 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.<ref>{{Cite journal|last=Avis|first=Duncan|last2=Power|first2=Dominic|date=2018-03-26|title=Axillary nerve injury associated with glenohumeral dislocation|journal=EFORT Open Reviews|volume=3|issue=3|pages=70–77|doi=10.1302/2058-5241.3.170003|issn=2058-5241|pmc=5890131|pmid=29657847}}</ref> ==Function== [[File:Deltoid muscle.JPG|thumb|right|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.<ref>Radiography of the Upper Extremities: 24 ARRT Category A. CE4RT, 2014. 201. Print.</ref> 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.<ref>{{Exrx|Muscles/DeltoidAnterior}}</ref> The lateral 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.<ref>{{Exrx|Muscles/DeltoidLateral}}</ref> 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.<ref>{{Exrx|Muscles/DeltoidPosterior}}</ref> An important function of the deltoid in humans is preventing the [[dislocation (medicine)|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.<ref name="Potau"/> The lateral 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.<ref>{{Cite web |url=http://muscleguide.co.uk/exercises/lateral-deltoid-raise.html |title=Archived copy |access-date=2013-06-17 |archive-url=https://web.archive.org/web/20120625202454/http://muscleguide.co.uk/exercises/lateral-deltoid-raise.html |archive-date=2012-06-25 |url-status=dead }}</ref> 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 muscle|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&nbsp;mm upward movement of the head of the humerus during the first 30° to 60° of arm elevation.<ref name="Potau"/> ==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 is the result of various causes, including aging, disuse, [[denervation]], [[muscular dystrophy]], [[cachexia]] and [[Iatrogenesis|iatrogenic injury]]. Deltoideal 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.<ref>Arend CF. Ultrasound of the Shoulder. Master Medical Books, 2013. Chapter on deltoideal enthesopathy available at [http://www.shoulderus.com/ultrasound-of-the-shoulder/deltoid-ultrasound-entesopathy/ ShoulderUS.com]</ref> ==Other animals== The deltoid is also found in members of the [[Hominidae|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&nbsp;gram compared to 191.9&nbsp;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.<ref name="Potau"/> ==References== {{Reflist|30em}} ==See also== {{Commons category|Deltoid muscle}} {{Anatomy-terms}}{{Muscles of upper limb}} {{Authority control}} {{DEFAULTSORT:Deltoid Muscle}} [[Category:Muscles of the upper limb]] [[Category:Shoulder abductors]] [[Category:Shoulder flexors]] [[Category:Shoulder medial rotators]] [[Category:Shoulder extensors]] [[Category:Shoulder lateral rotators]]'