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Scapula
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== Structure == The scapula is a thick, flat bone lying on the thoracic wall that provides an attachment for three groups of muscles: intrinsic, extrinsic, and stabilizing and rotating muscles. The intrinsic muscles of the scapula include the muscles of the [[rotator cuff]](SITS muscle)—the subscapularis, [[supraspinatus muscle|supraspinatus]], infraspinatus and teres minor.<ref>Marieb, E. (2005). Anatomy & Physiology (2nd ed.). San Francisco, CA: Pearson Benjamin Cummings.</ref> These muscles attach to the surface of the scapula and are responsible for the internal and external rotation of the [[shoulder joint]], along with [[humerus|humeral]] abduction. The extrinsic muscles include the [[biceps]], [[Triceps brachii muscle|triceps]], and [[deltoid muscle]]s and attach to the [[coracoid process]] and supraglenoid tubercle of the scapula, infraglenoid tubercle of the scapula, and [[spine of the scapula]]. These muscles are responsible for several actions of the glenohumeral joint. The third group, which is mainly responsible for stabilization and rotation of the scapula, consists of the [[trapezius]], [[Serratus anterior muscle|serratus anterior]], [[Levator scapulae muscle|levator scapulae]], and [[rhomboid muscles]]. These attach to the medial, superior, and inferior borders of the scapula. The head, processes, and the thickened parts of the bone contain [[cancellous]] tissue; the rest consists of a thin layer of compact tissue. The central part of the supraspinatus fossa and the upper part of the [[infraspinatous fossa]], but especially the former, are usually so thin in humans as to be semitransparent; occasionally the bone is found wanting in this situation, and the adjacent muscles are separated only by fibrous tissue. The scapula has two surfaces, three borders, three angles, and three processes. === Surfaces === [[File:Anatomy of Scapula.gif|thumb|3d model of scapula, along with annotations showing the various parts of the scapula]] ====Front or subscapular fossa==== The front of the scapula (also known as the costal or ventral surface) has a broad concavity called the '''subscapular fossa''', to which the [[subscapularis muscle]] attaches. The medial two-thirds of the fossa have 3 longitudinal oblique ridges, and another thick ridge adjoins the lateral border; they run outward and upward. The ridges give attachment to the tendinous insertions, and the surfaces between them to the fleshy fibers, of the subscapularis muscle. The lateral third of the fossa is smooth and covered by the fibers of this muscle. At the upper part of the fossa is a transverse depression, where the bone appears to be bent on itself along a line at right angles to and passing through the center of the [[glenoid cavity]], forming a considerable angle, called the subscapular angle; this gives greater strength to the body of the bone by its arched form, while the summit of the arch serves to support the [[spine of scapula|spine]] and [[acromion]]. The costal surface superior of the scapula is the origin of 1st digitation for the serratus anterior origin. {| class="wikitable" align="left" |+ Figure 1 : Left scapula. Costal surface. | [[File:Left scapula - close-up - animation - stop at anterior surface.gif|220px]] || [[File:Gray202.png|152px]] || [[File:Scapula ant numbered.png|175px]] || {{ordered list |[[Subscapular fossa]] |[[Glenoid cavity]] |[[Coracoid process]] |[[Acromion]] |[[Superior border of scapula|Superior border]] |[[Suprascapular notch|Scapular notch]] |[[Superior angle of scapula|Superior angle]] |[[Medial border of scapula|Medial border]] |[[Inferior angle of the scapula|Inferior angle]] |[[Lateral border of the scapula|Lateral border]] |[[Infraglenoid tubercle]]}} |} {{Clear}} ====Back==== The back of the scapula (also called the dorsal or posterior surface) is arched from above downward, and is subdivided into two unequal parts by the spine of the scapula. The portion above the spine is called the [[supraspinous fossa]], and that below it the [[infraspinous fossa]]. The two fossae are connected by the [[spinoglenoid notch]], situated lateral to the root of the spine. * The ''supraspinous fossa'', above the spine of scapula, is concave, smooth, and broader at its vertebral than at its humeral end; its medial two-thirds give origin to the [[Supraspinatus]]. At its lateral surface resides the spinoglenoid fossa which is situated by the medial margin of the [[glenoid fossa of scapula|glenoid]]. The spinoglenoid fossa houses the [[suprascapular canal]] which forms a connecting passage between the [[suprascapular notch]] and the [[spinoglenoid notch]] conveying the [[suprascapular nerve]] and vessels.<ref>{{cite journal |last1=Al-Redouan |first1=Azzat |last2=Holding |first2=Keiv |last3=Kachlik |first3=David |title="Suprascapular canal": Anatomical and topographical description and its clinical implication in entrapment syndrome |journal=Annals of Anatomy |date=2021 |volume=233 |page=151593 |doi=10.1016/j.aanat.2020.151593 |pmid=32898658 |doi-access= }}</ref> * The ''infraspinous fossa'' is much larger than the preceding; toward its vertebral margin a shallow concavity is seen at its upper part; its center presents a prominent convexity, while near the axillary border is a deep groove which runs from the upper toward the lower part. The medial two-thirds of the fossa give origin to the [[Infraspinatus]]; the lateral third is covered by this muscle. There is a ridge on the outer part of the back of the scapula. This runs from the lower part of the glenoid cavity, downward and backward to the vertebral border, about 2.5 cm above the inferior angle. Attached to the ridge is a fibrous septum, which separates the [[infraspinatus muscle]] from the [[Teres major]] and [[Teres minor]] muscles. The upper two-thirds of the surface between the ridge and the axillary border is narrow, and is crossed near its center by a groove for the scapular circumflex vessels; the [[Teres minor]] attaches here. The broad and narrow portions above alluded to are separated by an oblique line, which runs from the axillary border, downward and backward, to meet the elevated ridge: to it is attached a fibrous septum which separates the [[Teres (disambiguation)|Teres]] muscles from each other. Its lower third presents a broader, somewhat triangular surface, the '''inferior angle of the scapula''', which gives origin to the [[Teres major]], and over which the [[Latissimus dorsi]] glides; frequently the latter muscle takes origin by a few fibers from this part. {| class="wikitable" align="left" |+Figure 2 : Left scapula. Dorsal surface. |- | [[File:Left scapula - close-up - animation - stop at posterior surface.gif|220px]] || [[File:Gray203.png|153px]] || [[File:Scapula post numbered.png|172px]] | {{ordered list |[[Supraspinous fossa]] |[[Spine of scapula|Spine]] |[[Infraspinous fossa]] |[[Superior border of scapula|Superior border]] |[[Superior angle of scapula|Superior angle]] |[[Medial border of scapula|Medial border]] |[[Inferior angle of the scapula|Inferior angle]] |[[Lateral border of the scapula|Lateral border]] |[[Lateral angle of the scapula|Lateral angle]] |[[Acromion]] |[[Coracoid process]] |Origin of [[teres major muscle]] |Origin of [[teres minor muscle]]}} |} {{Clear}} ====Side==== The [[acromion]] forms the summit of the shoulder, and is a large, somewhat triangular or oblong process, flattened from behind forward, projecting at first laterally, and then curving forward and upward, so as to overhang the glenoid cavity. {| class="wikitable" align="left" |+Figure 3 : Left scapula. Lateral surface. |- | [[File:Left scapula - close-up - animation - stop at lateral surface.gif|260px]] || [[File:Gray205 left scapula lateral view.png|112px]] || [[File:LeftScapulaLateral.jpg|146px]] | {{ordered list |[[Coracoid process]] |[[Glenoid cavity]] |[[Supraspinous fossa]] |[[Acromion]] |[[Infraspinous fossa]] |[[Inferior angle of the scapula|Inferior angle]] |[[Lateral border of the scapula|Lateral border]]}} |} {{Clear}} === Angles === There are 3 angles: The '''superior angle of the scapula''' or '''medial angle''', is covered by the [[trapezius muscle]]. This angle is formed by the junction of the [[Superior border of scapula|superior]] and [[Medial border of scapula|medial borders]] of the scapula. The superior angle is located at the approximate level of the [[Thoracic vertebrae#Second thoracic vertebra|second]] [[Thoracic vertebrae|thoracic vertebra]]. The superior angle of the scapula is thin, smooth, rounded, and inclined somewhat lateralward, and gives attachment to a few fibers of the [[levator scapulae muscle]].<ref name="Gray's Anatomy 1918">{{cite book | title=Anatomy of the Human Body, 20th ed. / thoroughly rev. and re-edited by Warren H. Lewis. | publisher=Lea & Febiger | author=Gray, Henry | year=1918 | location=Philadelphia | pages=206|ol = 24786057M}}</ref> The '''inferior angle of the scapula''' is the lowest part of the scapula and is covered by the [[latissimus dorsi muscle]]. It moves forwards round the chest when the arm is abducted. The inferior angle is formed by the union of the medial and lateral borders of the scapula. It is thick and rough and its posterior or back surface affords attachment to the [[teres major]] and often to a few fibers of the latissimus dorsi. The [[Anatomical terms of location#Usage in human anatomy|anatomical plane]] that passes vertically through the inferior angle is named the [[scapular line]]. The '''lateral angle of the scapula''' or '''glenoid angle''', also known as the '''head of the scapula''', is the thickest part of the scapula. It is broad and bears the [[glenoid fossa]] on its articular surface which is directed forward, laterally and slightly upwards, and articulates with the [[head of the humerus]]. The inferior angle is broader below than above and its vertical diameter is the longest. The surface is covered with cartilage in the fresh state; and its margins, slightly raised, give attachment to a [[fibrocartilaginous]] structure, the [[glenoidal labrum]], which deepens the cavity. At its apex is a slight elevation, the [[supraglenoid tuberosity]], to which the long head of the [[biceps brachii]] is attached.<ref name="Al-Redouan and Kacklik 2022">{{cite journal |last1=Al-Redouan |first1=Azzat |last2=Kachlik |first2=David |title=Scapula revisited: new features identified and denoted by terms using consensus method of Delphi and taxonomy panel to be implemented in radiologic and surgical practice |journal=J Shoulder Elbow Surg |date=2022 |volume=31 |issue=2 |page=e68-e81 |doi=10.1016/j.jse.2021.07.020 |pmid=34454038 |url=https://www.jshoulderelbow.org/article/S1058-2746(21)00636-4/fulltext|url-access=subscription }}</ref> The '''anatomic neck of the scapula''' is the slightly constricted portion which surrounds the head and is more distinct below and behind than above and in front. The '''surgical neck of the scapula''' passes directly medial to the base of the coracoid process.<ref name="FrichLarsen2017">{{cite journal|last1=Frich|first1=Lars Henrik|last2=Larsen|first2=Morten Schultz|title=How to deal with a glenoid fracture|journal=EFORT Open Reviews|volume=2|issue=5|year=2017|pages=151–157|issn=2396-7544|doi=10.1302/2058-5241.2.160082|pmid=28630753|pmc=5467683|doi-access=free}}</ref> <gallery> File:Superior angle of left scapula01.png|Superior angle shown in red File:Head of scapula02.png|Lateral angle shown in red File:Scapula ant - anatomical neck and surgical neck.png|Anatomic neck: red, Surgical neck: purple File:Inferior angle of the left scapula01.png|Inferior angle shown in red </gallery> === Borders === {{anchor|border}}{{anchor|Lateral border of scapula}}{{anchor|Superior border of scapula}}{{anchor|Axillary border of scapula}}{{anchor|Medial border of scapula}} There are three borders of the scapula: * The '''superior border''' is the shortest and thinnest; it is concave, and extends from the [[superior angle]] to the base of the [[coracoid process]]. It is referred to as the cranial border in animals. ::At its lateral part is a deep, semicircular notch, the [[scapular notch]], formed partly by the base of the [[coracoid process]]. This notch is converted into a [[foramen]] by the [[superior transverse scapular ligament]], and serves for the passage of the [[suprascapular nerve]]; sometimes the ligament is [[ossified]]. ::The adjacent part of the superior border affords attachment to the [[omohyoideus]]. <gallery> File:Superior border of left scapula01.png|[[#Costal (Front, Ventral, Anterior)|Costal surface of left scapula]]. Superior border shown in red. File:Superior border of left scapula - animation01.gif|Left scapula. Superior border shown in red. File:Superior border of scapula - animation02.gif|Animation. Superior border shown in red. </gallery> * The '''axillary border''' (or "lateral border") is the thickest of the three. It begins above at the lower margin of the [[glenoid cavity]], and inclines obliquely downward and backward to the inferior angle. It is referred to as the caudal border in animals. ::It begins above at the lower margin of the [[glenoid cavity]], and inclines obliquely downward and backward to the [[inferior angle]]. ::Immediately below the glenoid cavity is a rough impression, the [[infraglenoid tuberosity]], about {{convert|2.5|cm|0|abbr=on}}. in length, which gives origin to the long head of the [[triceps brachii]]; in front of this is a longitudinal groove, which extends as far as the lower third of this border, and affords origin to part of the [[subscapularis]]. ::The inferior third is thin and sharp, and serves for the attachment of a few fibers of the [[teres major]] behind, and of the [[subscapularis]] in front. <gallery> File:Lateral border of left scapula01.png|[[#Dorsal (Back, Posterior)|Dorsal surface of left scapula]]. Lateral border shown in red. File:Lateral border of left scapula - animation.gif|Left scapula. Lateral border shown in red. File:Lateral border of scapula - animation.gif|Animation. Lateral border shown in red. </gallery> * The '''medial border''' (also called the vertebral border or medial margin) is the longest of the three borders, and extends from the superior angle to the inferior angle.<ref name="Shuenke 2010">{{Cite book|title = Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System|last = Shuenke|first = Michael|publisher = Everbest Printing Ltd.|year = 2010|isbn = 978-1-60406-286-1|location = New York}}</ref> In animals it is referred to as the '''dorsal border'''. ::Four muscles attach to the medial border. [[Serratus anterior]] has a long attachment on the anterior lip. Three muscles insert along the posterior lip, the [[levator scapulæ|levator scapulae]] (uppermost), [[Rhomboid minor muscle|rhomboid minor]] (middle), and to the [[rhomboideus major|rhomboid major]] (lower middle).<ref name="Shuenke 2010" /> <gallery> File:Medial boder of left scapula - animation.gif|Left scapula. Medial border shown in red. File:Medial boder of scapula - animation.gif|Animation. Medial border shown in red. File:Medial border of scapula01.png|Still image. Medial border shown in red. File:Levator scapulae.png|[[Levator scapulae muscle]] (red) File:Rhomboideus minor.png|[[Rhomboid minor muscle]] (red) File:Rhomboideus major.png|[[Rhomboid major muscle]] (red) </gallery> === Development === [[File:Gray206.png|thumb|'''Figure 5 :''' Plan of ossification of the scapula. From seven centers.]] The scapula is [[ossified]] from 7 or more centers: one for the body, two for the [[coracoid process]], two for the [[acromion]], one for the vertebral border, and one for the inferior angle. Ossification of the body begins about the second month of fetal life, by an irregular quadrilateral plate of bone forming, immediately behind the [[glenoid cavity]]. This plate extends to form the chief part of the bone, the [[Spine of scapula|scapular spine]] growing up from its [[dorsal surface]] about the third month. Ossification starts as membranous ossification before birth.<ref>{{cite web|url=http://www.gehealthcare.com/|title=GE Healthcare - Home|website=www.gehealthcare.com}}</ref><ref>{{cite book |url=https://books.google.com/books?id=t70Ij7jHLIkC&q=%22membranous+ossification%22+scapula&pg=PA97|title=Facial Trauma|isbn=978-0-8247-5008-4|last1=Thaller|first1=Seth|last2=Scott Mcdonald|first2=W|date=2004-03-23}}</ref> After birth, the cartilaginous components would undergo [[endochondral]] [[ossification]]. The larger part of the scapula undergoes membranous ossification.<ref>{{cite web|url=http://www.medcyclopaedia.com/library/topics/volume_vii/o/ossification.aspx|archive-url=https://archive.today/20110526162035/http://www.medcyclopaedia.com/library/topics/volume_vii/o/ossification.aspx|url-status=dead|archive-date=2011-05-26|title=Ossification|publisher=[[General Electric|GE]]|work=Medcyclopaedia}}</ref> Some of the outer parts of the scapula are cartilaginous at birth, and would therefore undergo endochondral ossification.<ref>{{cite web|url=http://www.bartleby.com/107/50.html|title=II. Osteology. 6a. 2. The Scapula (Shoulder Blade). Gray, Henry. 1918. Anatomy of the Human Body.}}</ref> At birth, a large part of the scapula is osseous, but the glenoid cavity, the coracoid process, the acromion, the vertebral border and the inferior angle are [[cartilaginous]]. From the 15th to the 18th month after birth, ossification takes place in the middle of the coracoid process, which as a rule becomes joined with the rest of the [[bone]] about the 15th year. Between the 14th and 20th years, the remaining parts ossify in quick succession, and usually in the following order: first, in the root of the coracoid process, in the form of a broad scale; secondly, near the base of the acromion; thirdly, in the inferior angle and contiguous part of the vertebral border; fourthly, near the outer end of the acromion; fifthly, in the vertebral border. The base of the acromion is formed by an extension from the spine; the two [[Nucleus (cell)|nuclei]] of the acromion unite, and then join with the extension from the spine. The upper third of the glenoid cavity is ossified from a separate center (sub coracoid), which appears between the 10th and 11th years and joins between the 16th and the 18th years. Further, an [[epiphysial plate]] appears for the lower part of the glenoid cavity, and the tip of the coracoid process frequently has a separate nucleus. These various [[epiphyses]] are joined to the bone by the 25th year. Failure of bony union between the acromion and spine sometimes occurs (see [[os acromiale]]), the junction being effected by [[fibrous tissue]], or by an imperfect articulation; in some cases of supposed [[fracture]] of the acromion with ligamentous union, it is probable that the detached segment was never united to the rest of the [[bone]]. {{blockquote|''"In terms of comparative anatomy the human scapula represents two bones that have become fused together; the (dorsal) scapula proper and the (ventral) coracoid. The epiphyseal line across the glenoid cavity is the line of fusion. They are the counterparts of the ilium and ischium of the pelvic girdle."''|R. J. Last – 'Last's Anatomy}}
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