The shoulder joint (or glenohumeral joint from Greek ''glene'', eyeball, + -''oid'', 'form of', + Latin ''humerus'',

shoulder The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder m ...

) is structurally classified as a synovial

ball-and-socket joint The ball-and-socket joint (or spheroid joint) is a type of synovial joint in which the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. The distal bone is capable of motion around an indefinite number of ...

and functionally as a diarthrosis and multiaxial joint. It involves an articulation between the glenoid fossa of the

scapula The scapula (: scapulae or scapulas), 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 ...

(shoulder blade) and the head of the

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

(upper arm bone). Due to the very loose

joint capsule In anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joint.glenoid labrum The glenoid labrum (glenoid ligament) is a fibrocartilaginous (but not fibrocartilage, as previously thought) structure attached around the rim of the glenoid cavity on the shoulder blade. The shoulder joint is considered a ball-and-socket joint ...

. The glenoid labrum is a ring of cartilaginous fibre attached to the circumference of the cavity. This ring is continuous with the

tendon A tendon or sinew is a tough band of fibrous connective tissue, dense fibrous connective tissue that connects skeletal muscle, muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tensi ...

of the

biceps brachii The biceps or biceps brachii (, "two-headed muscle of the arm") is a large muscle that lies on the front of the upper arm between the shoulder and the elbow. Both heads of the muscle arise on the scapula and join to form a single muscle bell ...

above.

Spaces

Significant joint spaces are: * The normal glenohumeral space is 4–5 mm. Subacromial space on outlet view X-ray

* The normal subacromial space in shoulder radiographs is 9–10 mm; this space is significantly greater in men, with a slight reduction with age. In middle age, a subacromial space less than 6 mm is pathological, and may indicate a rupture of the tendon of the

supraspinatus muscle The supraspinatus (: supraspinati) is a relatively small muscle of the upper back that runs from the supraspinous fossa superior portion of the scapula (shoulder blade) to the greater tubercle of the humerus. It is one of the four rotator cuff mus ...

. The

axillary space The axillary spaces are anatomic spaces. through which axillary contents leave the axilla. They consist of the quadrangular space, triangular space, and triangular interval. It is bounded by teres major, teres minor, medial border of the hume ...

is an

anatomic space {{set index article In anatomy, a spatium or anatomic space is a space (cavity or gap). Anatomic spaces are often landmarks to find other important structures. When they fill with gases (such as air) or liquids (such as blood) in pathological ways, ...

between the associated muscles of the shoulder. This space transmits the subscapular artery and the

axillary nerve The axillary nerve or the circumflex nerve is a nerve of the human body, that originates from the brachial plexus ( upper trunk, posterior division, posterior cord) at the level of the axilla (armpit) and carries nerve fibers from C5 and C6. ...

Capsule

The shoulder joint has a very loose

joint capsule In anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joint.dislocate. The "U shaped" dependent portion of the axillary part of the capsule ,located between the anterior and posterior bands of inferior glenohumeral ligament, is called "axillary pouch". Synovium extends below the long head of biceps and subscapularis tendon to form subscapular bursa. Therefore, long head of biceps is extrasynovial and intracapsular, attaching to supraglenoid tubercle.

Bursae

A number of small fluid-filled sacs known as

synovial bursa A synovial bursa, usually simply bursa (: bursae or bursas), is a small fluid-filled sac lined by synovial membrane with an inner capillary layer of viscous synovial fluid (similar in consistency to that of a raw egg white). It provides a cushi ...

e are located around the capsule to aid mobility: * Between the joint capsule and the

deltoid muscle The deltoid muscle is the muscle forming the rounded contour of the shoulder, human shoulder. It is also known as the 'common shoulder muscle', particularly in other animals such as the domestic cat. Anatomically, the deltoid muscle is made up o ...

is the subacromial-subdeltoid bursa. * Between the capsule and the

acromion In human anatomy, the acromion (from Greek: ''akros'', "highest", ''ōmos'', "shoulder", : acromia) or summit of the shoulder is a bony process on the scapula (shoulder blade). Together with the coracoid process, it extends laterally over the sh ...

is the subacromial bursa. * The subcoracoid bursa is between the capsule and the

coracoid process The coracoid process (from Greek κόραξ, raven) is a small hook-like structure on the lateral edge of the superior anterior portion of the scapula (hence: coracoid, or "like a raven's beak"). Pointing laterally forward, it, together with the ...

of the scapula. * The coracobrachial bursa is between the

subscapularis muscle The subscapularis is a large triangular muscle which fills the subscapular fossa and inserts into the lesser tubercle of the humerus and the front of the capsule of the shoulder-joint. Structure The subscapularis is covered by a dense fasci ...

and the tendon of the

coracobrachialis muscle The coracobrachialis muscle muscle in the upper medial part of the arm. It is located within the anterior compartment of the arm. It originates from the coracoid process of the scapula; it inserts onto the middle of the medial aspect of the body ...

. * Between the capsule and the tendon of the subscapularis muscle is the subscapular bursa, this is also known as the subtendinous bursa of the scapularis. The supra-acromial bursa does not normally communicate with the shoulder joint.

Muscles

The shoulder joint is muscle-dependent, as it lacks strong ligaments. The primary stabilizers of the shoulder include the biceps brachii on the anterior side of the arm and tendons of the

rotator cuff The rotator cuff (SITS muscles) is a group of muscles and their tendons that act to stabilize the human shoulder and allow for its extensive range of motion. Of the seven scapulohumeral muscles, four make up the rotator cuff. The four muscles a ...

, which are fused to all sides of the capsule except the inferior margin. The tendon of the long head of the biceps brachii passes through the bicipital groove on the humerus and inserts on the superior margin of the glenoid cavity to press the

head of the humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists o ...

against the glenoid cavity. Other long muscles such as pectoralis major,

latissimus dorsi The latissimus dorsi () is a large, flat muscle on the back that stretches to the sides, behind the arm, and is partly covered by the trapezius on the back near the midline. The word latissimus dorsi (plural: ''latissimi dorsi'') comes from L ...

teres major The teres major muscle is a muscle of the upper limb. It attaches to the scapula and the humerus and is one of the seven scapulohumeral muscles. It is a thick but somewhat flattened muscle. The teres major muscle (from Latin ''teres'', meanin ...

and deltoid muscles also provide support to the shoulder joint. The tendons of the rotator cuff and their respective muscles (

infraspinatus In human anatomy, the infraspinatus muscle is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa.''Gray's Anatomy'', see infobox. As one of the four muscles of the rotator cuff, the main function of the infraspin ...

, teres minor, and

subscapularis The subscapularis is a large triangular muscle which fills the subscapular fossa and inserts into the lesser tubercle of the humerus and the front of the capsule of the Glenohumeral joint, shoulder-joint. Structure The subscapularis is covere ...

) stabilize and fix the joint. The supraspinatus, infraspinatus and teres minor muscles aid in abduction and external rotation.

Ligaments

* Superior, middle and inferior glenohumeral ligaments. It is the thickenings of the capsule that passes from the upper part of glenoid to lesser tuberosity and inferior part of the head of humerus. These ligaments are weak unlike its posterior part which is supported by the

muscle. * Coracohumeral ligament *

Transverse humeral ligament The transverse humeral ligament (Brodie's ligament) forms a broad band bridging the lesser and greater tubercle of the humerus. Its attachments are limited superior to the epiphysial line. By enclosing the canal of the bicipital groove (inte ...

* Coraco-acromial ligament

Innervation

The nerves supplying the shoulder joint all arise in the

brachial plexus The brachial plexus is a network of nerves (nerve plexus) formed by the anterior rami of the lower four Spinal nerve#Cervical nerves, cervical nerves and first Spinal nerve#Thoracic nerves, thoracic nerve (cervical spinal nerve 5, C5, Cervical spi ...

. They are the

suprascapular nerve The suprascapular nerve is a mixed (sensory and motor) nerve that branches from the upper trunk of the brachial plexus. It is derived from the ventral rami of cervical nerves C5-C6. It provides motor innervation to the supraspinatus muscle, and t ...

, the

and the lateral pectoral nerve.

Blood supply

The shoulder joint is supplied with blood by branches of the

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

and posterior circumflex humeral arteries, the

suprascapular artery The suprascapular artery is a branch of the thyrocervical trunk on the neck. Structure At first, it passes downward and laterally across the scalenus anterior and phrenic nerve, being covered by the sternocleidomastoid muscle; it then crosses t ...

and the scapular circumflex artery.

Function

The

muscles of the shoulder produce a high tensile force, and help to pull the head of the humerus into the glenoid cavity. The glenoid cavity is shallow and contains the

glenoid labrum The glenoid labrum (glenoid ligament) is a fibrocartilaginous (but not fibrocartilage, as previously thought) structure attached around the rim of the glenoid cavity on the shoulder blade. The shoulder joint is considered a ball-and-socket joint ...

which deepens it and aids stability. With 120 degrees of unassisted flexion, the shoulder joint is the most mobile joint in the body. Shoulder muscle - force couple of rotator cuff

Shoulder muscle - force couple of rotator cuff

The movement of the scapula across the

rib cage The rib cage or thoracic cage is an endoskeletal enclosure in the thorax of most vertebrates that comprises the ribs, vertebral column and sternum, which protect the vital organs of the thoracic cavity, such as the heart, lungs and great ve ...

in relation to the humerus is known as the ''scapulohumeral rhythm'', and this helps to achieve a further range of movement. This range can be compromised by anything that changes the position of the scapula. This could be an imbalance in parts of the large

trapezius muscle The trapezius is a large paired trapezoid-shaped surface muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae of the human spine, spine and laterally to the spine of the scapula. It moves the scapula and ...

s that hold the scapula in place. Such an imbalance could cause a forward head carriage which in turn can affect the range of movements of the shoulder.

Movements

* Flexion and extension of the shoulder joint in the (

sagittal plane The sagittal plane (; also known as the longitudinal plane) is an anatomical plane that divides the body into right and left sections. It is perpendicular to the transverse and coronal planes. The plane may be in the center of the body and divi ...

). **Flexion is carried out by the anterior fibres of the deltoid, pectoralis major and the coracobrachialis. **Extension is carried out by the

and posterior fibres of the deltoid. * Abduction and adduction of the shoulder ( frontal plane). **Abduction is carried out by the deltoid and the supraspinatus in the first 90 degrees. From 90-180 degrees it is the trapezius and the

serratus anterior The serratus anterior is a muscle of the chest. It originates at the side of the chest from the upper 8 or 9 ribs; it inserts along the entire length of the anterior aspect of the medial border of the scapula. It is innervated by the long thor ...

. ** Adduction is carried out by the pectoralis major, latissimus dorsi, teres major and the subscapularis. * Horizontal abduction and horizontal adduction of the shoulder (transverse plane) * Medial and lateral rotation of the shoulder (also known as internal and external rotation). **Medial rotation is carried out by the anterior fibres of the deltoid, teres major, subscapularis, pectoralis major and the latissimus dorsi. **Lateral rotation is carried out by the posterior fibres of the deltoid, infraspinatus and the teres minor. * Circumduction of the shoulder (a combination of flexion/extension and abduction/adduction).

Clinical significance

The capsule can become inflamed and stiff, with abnormal bands of tissue ( adhesions) growing between the joint surfaces, causing pain and restricting the movement of the shoulder, a condition known as

frozen shoulder Adhesive capsulitis, also known as frozen shoulder, is a condition associated with shoulder pain and stiffness. It is a common shoulder ailment that is marked by pain and a loss of range of motion, particularly in external rotation. There is ...

or adhesive capsulitis. A

SLAP tear A SLAP tear or SLAP lesion is an injury to the superior glenoid labrum (fibrocartilaginous rim attached around the margin of the glenoid cavity in the shoulder blade) that initiates in the back of the labrum and stretches toward the front into the ...

(superior labrum anterior to posterior) is a rupture in the glenoid labrum. SLAP tears are characterized by shoulder pain in specific positions, pain associated with overhead activities such as tennis or overhand throwing sports, and weakness of the shoulder. This type of injury often requires surgical repair. Anterior dislocation of the glenohumeral joint occurs when the humeral head is displaced in the anterior direction. Anterior shoulder dislocation often is a result of a blow to the shoulder while the arm is in an abducted position. In younger people, these dislocation events are most commonly associated with fractures on the humerus and/or glenoid and can lead to recurrent instability. In older people, recurrent instability is rare but people often suffer rotator cuff tears. It is not uncommon for the arteries and nerves (

) in the axillary region to be damaged as a result of a shoulder dislocation; which if left untreated can result in weakness, muscle atrophy, or paralysis. Subacromial bursitis is a painful condition caused by

inflammation Inflammation (from ) is part of the biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The five cardinal signs are heat, pain, redness, swelling, and loss of function (Latin ''calor'', '' ...

which often presents a set of symptoms known as subacromial impingement.

Arthrography An arthrogram is a series of images of a joint after injection of a contrast medium, usually done by fluoroscopy or MRI. The injection is normally done under a local anesthetic such as Novocain or lidocaine. The radiologist or radiographer perfor ...

of shoulder joint (with or without

computed tomography A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

) is performed by injecting contrast below and lateral to the

to outline the shoulder joint. Axillary pouch of the shoulder can be seen on external rotation, while subscapular (subcoracoid) bursa can be seen on internal rotation of arm. The contrast should not enter subacromial bursa unless supraspinatus tendon is completely ruptured. MRI with surface coils is used to image the shoulder joint.

Additional images

File:Shoulder joint.svg, Diagram of the human shoulder joint, front view File:Shoulder joint back-en.svg, Diagram of the human shoulder joint, back view File:Gray326.png, The left shoulder and

acromioclavicular joint The acromioclavicular joint, or AC joint, is a joint at the top of the shoulder. It is the junction between the acromion (part of the scapula that forms the highest point of the shoulder) and the clavicle. It is a Plane joint, plane synovial joint ...

s, and the proper ligaments of the scapula File:Slide1KKKK.JPG, Dissection image of the coracohumeral ligament of the glenohumeral joint in green File:Slide7KKKK.JPG, Dissection image of the cartilage of the glenohumeral joint in green

References

External links

Shoulder Joint Movements

* * {{DEFAULTSORT:Glenohumeral Joint Joints Upper limb anatomy