Scapula
Scapula | |
---|---|
Details | |
Identifiers | |
Latin | scapula (omo) |
MeSH | D012540 |
TA98 | A02.4.01.001 |
TA2 | 1143 |
FMA | 13394 |
Anatomical terms of bone |
The scapula (pl.: scapulae or scapulas[1]), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). 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.
In compound terms, the prefix omo- is used for the shoulder blade in medical terminology. This prefix is derived from ὦμος (ōmos), the Ancient Greek word for shoulder, and is cognate with the Latin (h)umerus, which in Latin signifies either the shoulder or the upper arm bone.
The scapula forms the back of the
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—the subscapularis, teres minor, supraspinatus, and infraspinatus.[3] These muscles attach to the surface of the scapula and are responsible for the internal and external rotation of the shoulder joint, along with humeral abduction.
The extrinsic muscles include the
The third group, which is mainly responsible for stabilization and rotation of the scapula, consists of the trapezius, serratus anterior, 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
The central part of the supraspinatus fossa and the upper part of the
Surfaces
- 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
The costal surface superior of the scapula is the origin of 1st digitation for the serratus anterior origin.
|
- 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
- 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 spinoglenoid notch conveying the suprascapular nerve and vessels.[4]
- 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
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 muscles from each other.
Its lower third presents a broader, somewhat triangular surface, the inferior angle of the scapula, which gives origin to the
- 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.
|
Angles
There are 3 angles:
The superior angle of the scapula or medial angle, is covered by the
The inferior angle of the scapula is the lowest part of the scapula and is covered by the
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
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.[7]
-
Superior angle shown in red
-
Lateral angle shown in red
-
Anatomic neck: red, Surgical neck: purple
-
Inferior angle shown in red
Borders
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 ossified.
- The adjacent part of the superior border affords attachment to the omohyoideus.
- At its lateral part is a deep, semicircular notch, the
-
Costal surface of left scapula. Superior border shown in red.
-
Left scapula. Superior border shown in red.
-
Animation. Superior border shown in red.
- 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 inferior angle.
- Immediately below the glenoid cavity is a rough impression, the subscapularis.
- The inferior third is thin and sharp, and serves for the attachment of a few fibers of the subscapularisin front.
- It begins above at the lower margin of the
-
Dorsal surface of left scapula. Lateral border shown in red.
-
Left scapula. Lateral border shown in red.
-
Animation. Lateral border shown in red.
- 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.[8] In animals it is referred to as the dorsal border.
- Four muscles attach to the medial border. rhomboid major (lower middle).[8]
- Four muscles attach to the medial border.
-
Left scapula. Medial border shown in red.
-
Animation. Medial border shown in red.
-
Still image. Medial border shown in red.
-
Levator scapulae muscle (red)
-
Rhomboid minor muscle (red)
-
Rhomboid major muscle (red)
Development
The scapula is
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
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
Failure of bony union between the acromion and spine sometimes occurs (see
"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
Function
The following muscles attach to the scapula:
Muscle | Direction | Region |
Pectoralis Minor |
insertion | coracoid process |
Coracobrachialis |
origin | coracoid process |
Serratus Anterior | insertion | medial border
|
Triceps Brachii (long head) | origin | infraglenoid tubercle |
Biceps Brachii (short head) |
origin | coracoid process |
Biceps Brachii (long head) |
origin | supraglenoid tubercle |
Subscapularis |
origin | subscapular fossa
|
Rhomboid Major | insertion | medial border
|
Rhomboid Minor | insertion | medial border
|
Levator Scapulae | insertion | medial border
|
Trapezius | insertion | spine of scapula |
Deltoid | origin | spine of scapula |
Supraspinatus | origin | supraspinous fossa |
Infraspinatus |
origin | infraspinous fossa |
Teres Minor |
origin | lateral border
|
Teres Major |
origin | lateral border
|
Latissimus Dorsi (a few fibers, attachment may be absent) |
origin | inferior angle
|
Omohyoid |
origin | superior border
|
Movements
Movements of the scapula are brought about by the scapular muscles. The scapula can perform six actions:
- Elevation: upper levator scapulae
- Depression: lower trapezius
- Retraction (adduction): rhomboidsand middle trapezius
- Protraction (abduction): serratus anterior
- Upward rotation: upper and lower trapezius, serratus anterior
- Downward rotation: rhomboids,[13][14] Levator Scapulae, and Pec Minor
Clinical significance
Scapular fractures
Because of its sturdy structure and protected location,
An abnormally protruding inferior angle of the scapula is known as a winged scapula and can be caused by paralysis of the serratus anterior muscle. In this condition the sides of the scapula nearest the spine are positioned outward and backward. The appearance of the upper back is said to be wing-like. In addition, any condition causing weakness of the serratus anterior muscle may cause scapular "winging".
Scapular dyskenesis
The scapula plays an important role in shoulder impingement syndrome.[17]
Abnormal scapular function is called scapular dyskinesis. One action the scapula performs during a throwing or serving motion is elevation of the acromion process in order to avoid impingement of the rotator cuff tendons.[17] If the scapula fails to properly elevate the acromion, impingement may occur during the cocking and acceleration phase of an overhead activity. The two muscles most commonly inhibited during this first part of an overhead motion are the serratus anterior and the lower trapezius.[18] These two muscles act as a force couple within the glenohumeral joint to properly elevate the acromion process, and if a muscle imbalance exists, shoulder impingement may develop.
Other conditions associated with scapular dyskenesis include thoracic outlet syndrome and the related pectoralis minor syndrome.[19][20]
Etymology
The name scapula as synonym of shoulder blade is of Latin origin.[21] It is commonly used in medical English[21][22][23] and is part of the current official Latin nomenclature, Terminologia Anatomica.[24] Shoulder blade is the colloquial name for this bone.[citation needed]
In other animals
In fish, the scapular blade is a structure attached to the upper surface of the articulation of the
In the early tetrapods, these two structures respectively became the scapula and a bone referred to as the procoracoid (commonly called simply the "coracoid", but not homologous with the mammalian structure of that name). In amphibians and reptiles (birds included), these two bones are distinct, but together form a single structure bearing many of the muscle attachments for the forelimb. In such animals, the scapula is usually a relatively simple plate, lacking the projections and spine that it possesses in mammals. However, the detailed structure of these bones varies considerably in living groups. For example, in frogs, the procoracoid bones may be braced together at the animal's underside to absorb the shock of landing, while in turtles, the combined structure forms a Y-shape in order to allow the scapula to retain a connection to the clavicle (which is part of the shell). In birds, the procoracoids help to brace the wing against the top of the sternum.[25]
In the fossil therapsids, a third bone, the true coracoid, formed just behind the procoracoid. The resulting three-boned structure is still seen in modern monotremes, but in all other living mammals, the procoracoid has disappeared, and the coracoid bone has fused with the scapula, to become the coracoid process. These changes are associated with the upright gait of mammals, compared with the more sprawling limb arrangement of reptiles and amphibians; the muscles formerly attached to the procoracoid are no longer required. The altered musculature is also responsible for the alteration in the shape of the rest of the scapula; the forward margin of the original bone became the spine and acromion, from which the main shelf of the shoulder blade arises as a new structure.[25]
In dinosaurs
In
Gallery
-
3D image
-
Position of scapula (shown in red). Animation.
-
Shape of scapula (left). Animation.
-
Thorax seen from behind.
-
Diagram of the human shoulder joint, front view
-
Diagram of the human shoulder joint, back view
-
The scapular and circumflex arteries.
-
Left scapula. Dorsal surface. (Superior border labeled at center top.)
-
Scapula. Medial view.
-
Scapula. Anterior face.
-
Scapula. Posterior face.
-
Computer Generated turn around Image of scapula
-
Suprascapular canal path
-
Scapula Anatomy
See also
- Scapulimancy/Oracle bone the light side
References
- This article incorporates text in the public domain from page 202 of the 20th edition of Gray's Anatomy (1918)
- ^ O.D.E. 2nd Ed. 2005
- ^ "Scapula (Shoulder Blade) Anatomy, Muscles, Location, Function | EHealthStar". www.ehealthstar.com. 2 December 2014. Retrieved 2016-03-17.
- ^ Marieb, E. (2005). Anatomy & Physiology (2nd ed.). San Francisco, CA: Pearson Benjamin Cummings.
- PMID 32898658.
- OL 24786057M.
- PMID 34454038.
- PMID 28630753.
- ^ ISBN 978-1-60406-286-1.
- ^ "GE Healthcare - Home". www.gehealthcare.com.
- ISBN 978-0-8247-5008-4.
- ^ "Ossification". Medcyclopaedia. GE. Archived from the original on 2011-05-26.
- ^ "II. Osteology. 6a. 2. The Scapula (Shoulder Blade). Gray, Henry. 1918. Anatomy of the Human Body".
- PMID 24175141.
- ^ Saladin, K (2010). Anatomy & Physiology. McGraw-Hill.
- ISBN 0-07-137069-2.
- S2CID 11217081. Archived from the original(PDF) on 2009-09-19.
- ^ a b Kibler, BW. (1998). The role of the scapula in athletic shoulder function. The American Journal of Sports Medicine, 26(2), 325-337.
- ^ Cools, A., Dewitte, V., Lanszweert, F., Notebaert, D., Roets, A., et al. (2007). Rehabilitation of scapular muscle balance. The American Journal of Sports Medicine, 35(10), 1744.
- .
- PMC 10426640.
- ^ a b Anderson, D.M. (2000). Dorland’s illustrated medical dictionary (29th edition). Philadelphia/London/Toronto/Montreal/Sydney/Tokyo: W.B. Saunders Company.
- ^ Dorland, W.A.N. & Miller, E.C.L. (1948). ‘’The American illustrated medical dictionary.’’ (21st edition). Philadelphia/London: W.B. Saunders Company.
- ^ Dirckx, J.H. (Ed.) (1997).Stedman’s concise medical dictionary for the health professions. (3rd edition). Baltimore: Williams & Wilkins.
- ^ Federative Committee on Anatomical Terminology (FCAT) (1998). Terminologia Anatomica. Stuttgart: Thieme
- ^ ISBN 0-03-910284-X.
- Nickel, Schummer, & Seiferle; Lehrbuch der Anatomie der Haussäugetiere.
External links
- Anatomy photo:10:st-0301 at the SUNY Downstate Medical Center - "Joints of the Upper Extremity: Scapula"
- shoulder/bones/bones2 at the Dartmouth Medical School's Department of Anatomy
- shoulder/surface/surface2 at the Dartmouth Medical School's Department of Anatomy
- radiographsul at The Anatomy Lesson by Wesley Norman (Georgetown University) (xrayleftshoulder)