Editing Shoulder (section)

==Structure==
The shoulder consists of a ball-and-socket joint formed by the humerus and scapula and their surrounding structures - [[ligament]]s, [[muscle]]s, [[tendon]]s - which support the bones and maintain the relationship of one to another.<ref name=":0" /><ref name=":1" /> These supporting structures attach to the [[clavicle]], [[humerus]], and [[scapula]], the latter providing the [[glenoid cavity]], [[acromion]] and [[coracoid process]]es. The main [[joint]] of the shoulder is the [[shoulder joint]] (or glenohumeral joint), between the humerus and the glenoid process of the scapular.<ref name=":0" /> The [[acromioclavicular joint]] and sternoclavicular joint also play a role in shoulder movements.<ref name=":4">{{Cite book|title=Elsevier's Integrated Anatomy and Embryology|last=Bogart|first=Bruce|publisher=Elsevier|year=2007|isbn=978-1-4160-3165-9|pages=246–260}}</ref> White [[hyaline cartilage]] on the ends of the bones (called articular cartilage) allows the bones to glide and move on each other, and the joint space is surrounded by a synovial membrane. Around the joint space are muscles - the rotator cuff, which directly surrounds and attaches to the shoulder joint - and other muscles that help provide stability and facilitate movement.

Two filmy sac-like structures called [[bursa (anatomy)|bursa]]e permit smooth gliding between bone, muscle, and tendon. They cushion and protect the rotator cuff from the bony arch of the acromion.<ref>{{cite book |last1=Wexler |first1=Barbara |title=Encyclopedia of Nursing and Allied Health Vol. 1 |date=2006 |publisher=Gale |location=Farmington Hills, MI |isbn=978-1-4144-0374-8 |pages=414–416 |edition=2nd}}</ref>

The [[glenoid labrum]] is the second kind of cartilage in the shoulder which is distinctly different from the articular cartilage. This cartilage is more fibrous or rigid than the cartilage on the ends of the ball and socket. Also, this cartilage is also found only around the socket where it is attached.<ref>{{cite web|url=http://www.hopkinsortho.org/labrum_tear.html|title=labrum tear|publisher=Johns Hopkins Orthopaedic Surgery|access-date=2010-05-16|archive-url=https://web.archive.org/web/20111120005215/http://www.hopkinsortho.org/labrum_tear.html|archive-date=2011-11-20}}</ref>

===Joint===
{{main|Shoulder joint}}
[[File:Blausen 0797 ShoulderJoint.png|thumb|250px|Cross-section of shoulder joint]]

The [[shoulder joint]] (also known as the glenohumeral joint) is the main joint of the shoulder.<ref name=":0" /> It is a [[ball and socket joint]] that allows the arm to rotate in a circular fashion or to hinge out and up away from the body.  It is formed by the articulation between the head of the humerus and the lateral scapula (specifically-the glenoid cavity of the scapula).  The "ball" of the joint is the rounded, medial anterior surface of the humerus and the "socket" is formed by the glenoid cavity, the dish-shaped portion of the lateral scapula.  The shallowness of the cavity and relatively loose connections between the shoulder and the rest of the body allows the arm to have tremendous mobility, at the expense of being much easier to [[joint dislocation|dislocate]] than most other joints in the body. There is an approximately 4-to-1 disproportion in size between the large head of the humerus and the shallow glenoid cavity.{{citation needed|date=May 2015}}The glenoid cavity is made deeper by the addition of the fibrocartilaginous ring of the [[glenoid labrum]].

The [[joint capsule|capsule]] is a soft tissue envelope that encircles the glenohumeral joint and attaches to the scapula, humerus, and head of the [[biceps]]. It is lined by a thin, smooth [[synovial membrane]].  This capsule is strengthened by the coracohumeral ligament which attaches the coracoid process of the scapula to the greater tubercle of the humerus.  There are also three other ligaments attaching the lesser tubercle of the humerus to lateral scapula and are collectively called the glenohumeral ligaments.{{citation needed|date=May 2015}}

The [[transverse humeral ligament]], which passes from the [[Lesser tubercle of humerus|lesser tubercle]] to the [[greater tubercle of humerus]], covers the [[intertubercular groove]], in which the long head of [[biceps brachii]] travels.{{citation needed|date=May 2015}}

===Rotator cuff===
{{Main|Rotator cuff}}
[[File:Shoulder joint.svg|thumb|Shoulder anatomy, front view]]
[[File:Shoulder joint back-en.svg|thumb|Shoulder anatomy, back view]]
The [[rotator cuff]] is an anatomical term given to the group of four muscles and their tendons that act to stabilize the shoulder.<ref name=":4" /> These muscles are the [[supraspinatus muscle|supraspinatus]], [[infraspinatus muscle|infraspinatus]], [[teres minor muscle|teres minor]] and [[subscapularis muscle|subscapularis]] and that hold the head of the humerus in the glenoid cavity during movement.<ref name=":4" /> The cuff adheres to the glenohumeral capsule and attaches to the [[humeral head|head of the humerus]].<ref name=":4" /> Together, these keep the humeral head in the [[glenoid cavity]], preventing upward migration of the [[humeral head]] caused by the pull of the [[deltoid muscle]] at the beginning of arm elevation. The infraspinatus and the teres minor, along with the anterior fibers of the deltoid muscle, are responsible for external rotation of the arm.<ref name="favard">{{cite journal|last2=Bacle|first2=Guillaume|last3=Berhouet|first3=Julien|year=2007|title=Rotator cuff repair|journal=Joint Bone Spine|volume=74|issue=6|pages=551–7|doi=10.1016/j.jbspin.2007.08.003|pmid=17993287|last1=Favard|first1=Luc}}</ref>

The four [[tendon]]s of these muscles converge to form the rotator cuff tendon.  This tendon, along with the articular capsule, the [[coracohumeral ligament]], and the [[glenohumeral ligament]] complex, blend into a confluent sheet before insertion into the humeral tuberosities.<ref name="matava">{{cite journal |doi=10.1177/0363546505280213 |pmid=16127127 |title=Partial-Thickness Rotator Cuff Tears |journal=American Journal of Sports Medicine |volume=33 |issue=9 |pages=1405–17 |year=2005 |last1=Matava |first1=M. J. |last2=Purcell |first2=D. B. |last3=Rudzki |first3=J. R. |s2cid=29959313 }}</ref>  The [[infraspinatus]] and [[teres minor]] fuse near their [[musculotendinous junction]]s, while the [[supraspinatus]] and [[subscapularis]] tendons join as a sheath that surrounds the biceps tendon at the entrance of the bicipital groove.<ref name="matava" />

===Other muscles===
'''Muscles from the shoulder region'''

In addition to the four muscles of the rotator cuff, the [[deltoid muscle]] and [[teres major muscle]]s arise and exist in the shoulder region itself.<ref name=":4" /> The deltoid muscle covers the shoulder joint on three sides, arising from the front upper third of the clavicle, the acromion, and the spine of the scapula, and travelling to insert on the deltoid tubercle of the humerus.<ref name=":4" /> Contraction of each part of the deltoid assists in different movements of the shoulder - flexion (clavicular part), abduction (middle part) and extension (scapular part).<ref name=":4" /> The teres major attaches to the outer part of the back of the scapula, beneath the teres minor, and attaches to the upper part of the humerus. It helps with medial rotation of the humerus.<ref name=":4" />

'''Muscles from the front'''

Muscles from the chest wall that contribute to the shoulder are:<ref name=":4" />

{| class="wikitable"
|-
| '''Name''' || '''Attachment''' || '''Function'''
|-
| [[serratus anterior]] || Originates on the surface of the upper eight [[ribs]] at the side of the chest and inserts along the entire anterior length of the medial border of the scapula.<ref name=":4" /> || It fixes the scapula into the thoracic wall and aids in rotation and abduction of the shoulders.{{citation needed|date=May 2015}}
|-
| [[subclavius]] || Located beneath the clavicle, originating from the [[first rib]] and inserting on the [[subclavian groove]] of the clavicle.<ref name=":4" />  || It depresses the lateral clavicle<ref name=":4" /> and also acts to stabilize the clavicle.{{citation needed|date=May 2015}}
|-
| [[pectoralis minor]]  || Arises from the third, fourth, and fifth ribs, near their cartilage and inserts into the medial border and upper surface of the [[coracoid process]] of the scapula.<ref name=":4" />   || This muscle aids in respiration, medially rotates the scapula, protracts the scapula, and also draws the scapula inferiorly.
|-
| [[sternocleidomastoid]]  || Attaches to the [[Human sternum|sternum]] (sterno-), the [[clavicle]] (cleido-), and the [[mastoid process]] of the [[temporal bone]] of the skull. || Most of its actions flex and rotate the head.  In regards to the shoulder, however, it also aids in respiration by elevating the sternoclavicular joint when the head is fixed.{{citation needed|date=May 2015}}
|-
| [[levator scapulae]] || Arises from the transverse processes of the first four [[cervical vertebrae]] and inserts into the [[medial border of the scapula]]. || It is capable of rotating the scapula downward and elevating the scapula.{{citation needed|date=May 2015}}
|}
'''Muscles from the back'''
{| class="wikitable"
|-
| [[rhomboid major]] and [[rhomboid minor]] (work together) || They arise from the [[spinous processes]] of the [[thoracic vertebrae]] T1 to T5 as well as from the spinous processes of the seventh cervical. They attach to the inner border of the scapula.<ref name=":4" />  || They are responsible for downward rotation of the scapula with the levator scapulae, as well as adduction of the scapula.
|-
| [[trapezius]]  || Arises from the [[occipital bone]], the [[ligamentum nuchae]], the spinous process of the seventh cervical, and the spinous processes of all the thoracic vertebrae.<ref name=":4" />  It attaches to the outer clavicle, the [[acromion process]], and into the [[spine of the scapula]].<ref name=":4" />  || Different portions of the fibers perform different actions on the scapula: depression, upward rotation, elevation, and retraction.<ref name=":4" />
|-
| [[levator scapulae]]
|Arises from the transverse processes of cervical vertebrae 1-4, and attaches to the upper part of the inner border of the scapula.<ref name=":4" />
|Elevates the scapula.<ref name=":4" />
|-
| [[latissimus dorsi]]
|A large muscle that arises from the spinous processes of the lower six thoracic vertebrae, lumbar and all sacral vertebrae, and posterior iliac crest. It attaches to the intertubercular groove of the humerus.<ref name=":4" />
|Adducts, extends and rotates the humerus inwards.<ref name=":4" />
|}

=== Armpit ===
The armpit ({{Langx|la|axilla}}) is formed by the space between the muscles of the shoulder.<ref name=":4" /> The nerves and blood vessels of the arm travel through the armpit, and it possesses several sets of lymph nodes that are able to be examined.<ref name=":4" /> The armpit is formed by the pectoralis major and minor muscles at the front, the latissimus dorsi and teres major muscles at the back, the serratus anterior muscle on its inner surface, and the intertubercular groove of the humerus on the outer side.<ref name=":4" />

=== Nerve supply and passage ===
[[File:Gray523.png|thumb|The [[brachial plexus]] surrounds the axillary artery and is formed from nerve roots from C5-T1. Branches of the plexus supply the shoulder region, although several other nerves play a role.]]
[[File:Grant 1962 664.png|thumb|Nerve roots that supply sensation to the shoulder and arm]]
[[File:Gray812and814.svg|thumb|Nerves that supply sensation to the shoulder and arm]]
The skin around the shoulder is supplied by C2-C4 (upper), and C7 and T2 (lower area).{{Citation needed|date=November 2016}} The brachial plexus emerges as nerve roots from the cervical vertebrae C5-T1. Branches of the plexus, in particular from C5-C6, supply the majority of the muscles of the shoulder.<ref name=":4" />

=== Blood vessels ===
The subclavian artery arises from the brachiocephalic trunk on the right and directly from the aorta from the left. {{Citation needed|date=November 2016}} This becomes the [[axillary artery]] as it passes beyond the first rib. The axillary artery also supplies blood to the arm, and is one of the major sources of blood to the shoulder region. The other major sources are the [[transverse cervical artery]] and the [[suprascapular artery]], both branches of the [[thyrocervical trunk]] which itself is a branch of the subclavian artery.<ref name=":4" /> The blood vessels form a network (anastamosis) behind the shoulder that helps to supply blood to the arm even when the axillary artery is compromised.<ref name=":4" />
[[File:Text-book of anatomy and physiology for nurses (1913) (14764575614).jpg|thumb|The [[axillary artery]] supplies blood to the arm and is one of the major sources of blood for the shoulder region.]]