Scapula

In anatomy

Anatomy

Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...

, the scapula (Medical Latin), omo, or shoulder blade, is the bone

Bone

Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

 that connects the humerus

Humerus

The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....

 (upper arm bone) with the clavicle

Clavicle

In human anatomy, the clavicle or collar bone is a long bone of short length that serves as a strut between the scapula and the sternum. It is the only long bone in body that lies horizontally...

 (collar bone).

The scapula forms the posterior (back) located part of the shoulder

Shoulder

The human shoulder is made up of three bones: the clavicle , the scapula , and the humerus as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The major joint of the shoulder is the glenohumeral joint, which...

 girdle. In human

Human

Humans are the only living species in the Homo genus...

s, it is a flat bone, roughly triangular

Triangle

A triangle is one of the basic shapes of geometry: a polygon with three corners or vertices and three sides or edges which are line segments. A triangle with vertices A, B, and C is denoted ....

 in shape, placed on a posterolateral aspect of the thoracic cage.

Surfaces

Costal (Front, Ventral, Anterior)

The costal or ventral surface [Fig. 1] presents a broad concavity, the subscapular fossa.

The medial two-thirds of this fossa are marked by several oblique ridges, which run lateralward and upward. The ridges give attachment to the tendinous insertions, and the surfaces between them to the fleshy fibers, of the Subscapularis. The lateral third of the fossa is smooth and covered by the fibers of this muscle.

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Figure 1 : Left scapula. Costal surface.

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Figure 2 : Left scapula. Dorsal surface.

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Figure 3 : Left scapula. Lateral surface.

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

Glenoid cavity

The glenoid cavity is a shallow pyriform, articular surface, which is located on the lateral angle of the scapula. It is directed laterally and forward and articulates with the head of the humerus; it is broader below than above and its vertical diameter is the longest.This cavity forms the...

, 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

Vertebral column

In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...

 and acromion.

Dorsal (Back, Posterior)

The dorsal surface [Fig. 2] is arched from above downward, and is subdivided into two unequal parts by the spine; the portion above the spine is called the supraspinous fossa, and that below it the infraspinous fossa.

• The supraspinous fossa, the smaller of the two, is concave, smooth, and broader at its vertebral than at its humeral end; its medial two-thirds give origin to the Supraspinatus.

• 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.

The dorsal surface is marked near the axillary border by an elevated ridge, which runs from the lower part of the glenoid cavity, downward and backward to the vertebral border, about 2.5 cm above the inferior angle.

The ridge serves for the attachment of a fibrous septum, which separates the Infraspinatus from the Teres major and Teres minor.

The surface between the ridge and the axillary border is narrow in the upper two-thirds of its extent, and is crossed near its center by a groove for the passage of the scapular circumflex vessels; it affords attachment to the Teres minor.

Its lower third presents a broader, somewhat triangular surface, 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.

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

Teres

Teres I , was the first king of the Odrysian state of Thrace. Teres, who united the 40 or more Thracian tribes under one banner, was well-known for his military abilities and spent much of his life on the battlefield. He died during a military campaign in 445 BC...

 muscles from each other.

Borders

There are three borders of the scapula:

• The superior border
  Superior border of scapula
  Of the three borders of the scapula, the superior border is the shortest and thinnestit is concave, and extends from the medial angle to the base of the coracoid process....
  
   is the shortest and thinnest; it is concave, and extends from the medial angle to the base of the coracoid process. It is referred to as the cranial border in animals.

• The axillary border (or "lateral border") is the thickest of the three. It begins above at the lower margin of the glenoid cavity
  Glenoid cavity
  The glenoid cavity is a shallow pyriform, articular surface, which is located on the lateral angle of the scapula. It is directed laterally and forward and articulates with the head of the humerus; it is broader below than above and its vertical diameter is the longest.This cavity forms the...
  
  , and inclines obliquely downward and backward to the inferior angle. It is referred to as the caudal border in animals.

• The vertebral border (or "medial border") is the longest of the three, and extends from the medial to the inferior angle. It is referred to as the dorsal border in animals.

Angles

There are 3 angles -
1) The superior angle is covered by trapezius.
2) The inferior angle is covered by latissimus dorsi. It moves forwards round the chest when the arm is abducted.
3) The lateral or glenoid angle is broad and bears the glenoid cavity or fossa, which is directed forward, laterally and slightly upwards.

The acromion

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.

Development

The larger part of the scapula undergoes membranous ossification.http://www.medcyclopaedia.com/library/topics/volume_vii/o/ossification.aspx. Some of the outer parts of the scapula are cartilaginous at birth, and would therefore undergo endochondral ossification http://www.bartleby.com/107/50.html.

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

Infraspinatous fossa

The infraspinatous fossa of the scapula is much larger than the supraspinatous fossa; 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...

, 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.

Muscular attachments

The following muscles attach to the scapula:

Muscle

Direction

Region >- | Pectoralis Minor

insertion

>- | Coracobrachialis

origin

>- | Serratus Anterior Serratus anterior muscle The serratus anterior is a muscle that originates on the surface of the upper eight or nine ribs at the side of the chest and inserts along the entire anterior length of the medial border of the scapula.-Origin:...

insertion

medial border Medial border of scapula The medial border of the scapula is the longest of the three borders, and extends from the medial to the inferior angle.... >- | Triceps Brachii (long head)

origin

infraglenoid tubercle Infraglenoid tubercle The infraglenoid tubercle is the part of the scapula to which the long head of the triceps brachii attaches.-External links: - "Axillary Region: Scapula "... >- | Biceps Brachii Biceps brachii muscle In human anatomy, the biceps brachii, or simply biceps in common parlance, is, as the name implies, a two-headed muscle located on the upper arm. Both heads arise on the scapula and join to form a single muscle belly which is attached to the upper forearm...  (short head)

origin

>- | Biceps Brachii Biceps brachii muscle In human anatomy, the biceps brachii, or simply biceps in common parlance, is, as the name implies, a two-headed muscle located on the upper arm. Both heads arise on the scapula and join to form a single muscle belly which is attached to the upper forearm...  (long head)

origin

supraglenoid tubercle Supraglenoid tubercle The supraglenoid tubercle is a region of the scapula to which the long head of the biceps brachii muscle attaches. It is a small, rough projection just superior to the Glenoid cavity near the base of the coracoid process... >- | Subscapularis

origin

subscapular fossa Subscapular fossa The costal or ventral surface of the scapula presents a broad concavity, the subscapular fossa.It provides an attachment for the subscapularis muscle.-External links: - "Scapular Region: Scapula "... >- | Rhomboid Major Rhomboid major muscle The rhomboid major is a skeletal muscle on the back that connects the scapula with the vertebrae of the spinal column. In human anatomy, it acts together with the rhomboid minor to keep the scapula pressed against thoracic wall and to retract the scapula toward the vertebral column.-Structure:The...

insertion

medial border Medial border of scapula The medial border of the scapula is the longest of the three borders, and extends from the medial to the inferior angle.... >- | Rhomboid Minor Rhomboid minor muscle In human anatomy, the rhomboid minor is a small skeletal muscle on the back that connects the scapula with the vertebrae of the spinal column....

insertion

medial border Medial border of scapula The medial border of the scapula is the longest of the three borders, and extends from the medial to the inferior angle.... >- | Levator Scapulae Levator scapulae muscle In human anatomy, the levator scapulae is a skeletal muscle situated at the back and side of the neck. As the name suggests, its main function is to lift the scapula.-Origin and insertion:...

insertion

medial border Medial border of scapula The medial border of the scapula is the longest of the three borders, and extends from the medial to the inferior angle.... >- | Trapezius

insertion

spine of scapula Spine of scapula The spine of the scapula is a prominent plate of bone, which crosses obliquely the medial four-fifths of the scapula at its upper part, and separates the supra- from the infraspinatous fossa.... >- | Deltoid Deltoid muscle In human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. 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 central...

origin

spine of scapula Spine of scapula The spine of the scapula is a prominent plate of bone, which crosses obliquely the medial four-fifths of the scapula at its upper part, and separates the supra- from the infraspinatous fossa.... >- | Supraspinatus Supraspinatus muscle The supraspinatus is a relatively small muscle of the upper arm that runs from the supraspinatous fossa superior 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...

origin

>- | Infraspinatus

origin

>- | Teres Minor

origin

>- | Teres Major

origin

>- | Latissimus Dorsi (a few fibers)

origin

>- | Omohyoid

origin

superior border Superior border of scapula Of the three borders of the scapula, the superior border is the shortest and thinnestit is concave, and extends from the medial angle to the base of the coracoid process....

Movements

Movements of the scapula are brought about by scapular muscles:

Elevation,
Depression,
Protraction (abduction)
Retraction (adduction)
Upward (lateral) rotation,
Downward (medial) rotation,
Anterior Tipping,
and
Posterior Tipping

Injury

Because of its sturdy structure and protected location, scapular fractures are uncommon; when they do occur, they are an indication that severe chest trauma

Chest trauma

Chest trauma is a serious injury of the chest. Thoracic trauma is a common cause of significant disability and mortality, the leading cause of death from physical trauma after head and spinal cord injury. Blunt thoracic injuries are the primary or a contributing cause of about a quarter of all...

 has occurred.

A winged scapula

Winged scapula

A winged scapula is a condition in which the shoulder blade, or shoulder bone, protrudes from a person’s back in an abnormal position. It is a rare condition with the potential to lead to limited functional activity in the upper extremity with which it is adjacent. It can affect a person’s ability...

 is a condition in which the medial border (the side nearest the spine) of a person's scapula is abnormally positioned outward and backward. The resulting appearance of the upper back is said to be wing-like because the inferior angle of the shoulder blade protrudes backward rather than lying mostly flat. In addition, any condition causing weakness of the serratus anterior muscle may cause scapular "winging".

In other animals

In fish, the scapular blade is a structure attached to the upper surface of the articulation of the pectoral fin, and is accompanied by a similar coracoid plate on the lower surface. Although sturdy in cartilagenous fish

Chondrichthyes

Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone...

, both plates are generally small in most other fish, and may be partially cartilagenous, or consist of multiple bony elements.

In the early tetrapod

Tetrapod

Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...

s, these two structures respectively became the scapula and a bone referred to as the procoracoid (commonly called simply the "coracoid", but not homologous

Homology (biology)

Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...

 with the mammalian structure of that name). In amphibians and reptiles (birds inclused), 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

Sternum

The sternum or breastbone is a long flat bony plate shaped like a capital "T" located anteriorly to the heart in the center of the thorax...

.

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 monotreme

Monotreme

Monotremes are mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals...

s, 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.

As a shovel

In neolithic

Neolithic

The Neolithic Age, Era, or Period, or New Stone Age, was a period in the development of human technology, beginning about 9500 BC in some parts of the Middle East, and later in other parts of the world. It is traditionally considered as the last part of the Stone Age...

 times and earlier a large animal's scapula was often used as a crude shovel.http://books.google.co.uk/books?id=iSd8hm5kImwC&pg=PA304&lpg=PA304&dq=(%22shoulder+blade%22+OR+scapula)+shovel&source=bl&ots=cYk1nZRZGW&sig=q94kMqBrqjxDxyN3TN2LvrWoLII&hl=en&ei=DjY6TP3gIYP7lwfi-OjSBw&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCAQ6AEwAw#v=onepage&q=(%22shoulder%20blade%22%20OR%20scapula)%20shovel&f=false

See also

• Bone terminology
• Scapulimancy
  Scapulimancy
  Scapulimancy is the practice of divination by use of scapulae...
  
  /Oracle bone
  Oracle bone
  Oracle bones are pieces of bone normally from ox scapula or turtle plastron which were used for divination chiefly during the late Shang Dynasty. The bones were first inscribed with divination in oracle bone script by using a bronze pin, and then heated until crack lines appeared in which the...
  
  
• Terms for anatomical location

External links

- "Joints of the Upper Extremity: Scapula"