Shoulder joint

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Shoulder joint
Gray327.png
The right shoulder and shoulder joint
Details
Identifiers
Latin articulatio humeri
MeSH D012785
TA98 A03.5.08.001
TA2 1764
FMA 25912
Anatomical terminology

The shoulder joint (or glenohumeral joint from Greek glene, eyeball, + -oid, 'form of', + Latin humerus, shoulder) is structurally classified as a synovial ball-and-socket joint and functionally as a diarthrosis and multiaxial joint. It involves an articulation between the glenoid fossa of the scapula (shoulder blade) and the head of the humerus (upper arm bone). Due to the very loose joint capsule, it gives a limited interface of the humerus and scapula, it is the most mobile joint of the human body.

Contents

Structure

Cross-section of shoulder joint Blausen 0797 ShoulderJoint.png
Cross-section of shoulder joint

The shoulder joint is a ball-and-socket joint between the scapula and the humerus. The socket of the glenoid fossa of the scapula is itself quite shallow, but it is made deeper by the addition of the glenoid labrum. The glenoid labrum is a ring of cartilaginous fibre attached to the circumference of the cavity. This ring is continuous with the tendon of the biceps brachii above.

Spaces

Significant joint spaces are:

Supraspinatus outlet view X-ray, showing subacromial space measurement Subacromial space on outlet view X-ray.jpg
Supraspinatus outlet view X-ray, showing subacromial space measurement

The axillary space is an anatomic space between the associated muscles of the shoulder. This space transmits the subscapular artery and the axillary nerve.

Capsule

The shoulder joint has a very loose joint capsule, which can sometimes predispose the shoulder to dislocate.[ citation needed ]

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". [3]

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. [4]

Bursae

Bursae of shoulder joint: (1) and (6) subacromial-subdeltoid bursa, (2) subscapular recess, (3) subcoracoid bursa, (4) coracoclavicular bursa, (5) supra-acromial bursa Bursae shoulder joint normal.jpg
Bursae of shoulder joint: (1) and (6) subacromial-subdeltoid bursa, (2) subscapular recess, (3) subcoracoid bursa, (4) coracoclavicular bursa, (5) supra-acromial bursa

A number of small fluid-filled sacs known as synovial bursae are located around the capsule to aid mobility:

The supra-acromial bursa does not normally communicate with the shoulder joint.

Muscles

The shoulder joint is a muscle-dependent joint 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; which are fused to all sides of the capsule except the inferior margin. [5]

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 against the glenoid cavity. [5] Other long muscles such as pectoralis major, latissimus dorsi, teres major and deltoid muscles also provide support to the shoulder joint. [4]

The tendons of the rotator cuff and their respective muscles (supraspinatus muscle, infraspinatus, teres minor, and subscapularis) stabilize and fix the joint. [4] The supraspinatus, infraspinatus and teres minor muscles aid in abduction and external rotation. [6]

Ligaments

Innervation

The nerves supplying the shoulder joint all arise in the brachial plexus. They are the suprascapular nerve, the axillary nerve and the lateral pectoral nerve.

Anatomical illustration of the brachial plexus
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Wikimedia Commons has media related to this diagram
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with areas of roots, trunks, divisions and cords marked. Clicking on names of branches will link to their Wikipedia entry. Brachial plexus 2.svgDorsal scapular nerve (rhomboids, levator scapulae)Suprascapular nerve (supraspinatus, infraspinatus)Nerve to subclavius (subclavius)Lateral pectoral nerve (pectoralis major)Musculocutaneous nerve (coracobrachialis, brachialis, biceps brachii)Axillary nerve (deltoid, teres minor)Median nerve (forearm flexors except FCU and radial part of FDP, thenar muscles)Ulnar nerve (FCU and ulnar part of FDP, most intrinsic hand musclesRadial nerve (triceps brachii, supinator, anconeus, forearm extensors, brachioradialis)Lower subscapular nerve (lower part of subscapularis, teres major)Thoracodorsal nerve (latissimus dorsi)Medial pectoral nerve (pectoralis major, pectoralis minor)Upper subscapular nerve (upper part of subscapularis)Long thoracic nerve of Bell (serratus anterior)
Anatomical illustration of the brachial plexus with areas of roots, trunks, divisions and cords marked. Clicking on names of branches will link to their Wikipedia entry.

Blood supply

The shoulder joint is supplied with blood by branches of the anterior and posterior circumflex humeral arteries, the suprascapular artery and the scapular circumflex artery.

Function

Animation of shoulder joint showing the supraspinatus muscle Shoulder motion with rotator cuff (supraspinatus).gif
Animation of shoulder joint showing the supraspinatus muscle

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

Animation of the shoulder joint. The muscles shown are subscapularis muscle (at right), infraspinatus muscle (at top left), teres minor muscle (at bottom left) Shoulder muscle - force couple of rotator cuff.gif
Animation of the shoulder joint. The muscles shown are subscapularis muscle (at right), infraspinatus muscle (at top left), teres minor muscle (at bottom left)

The movement of the scapula across the rib cage 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 muscles 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

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 or adhesive capsulitis.

A SLAP tear (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. [8]

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. [9] It is not uncommon for the arteries and nerves (axillary nerve) 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. [10]

Subacromial bursitis is a painful condition caused by inflammation which often presents a set of symptoms known as subacromial impingement.

Arthrography of shoulder joint (with or without computed tomography) is performed by injecting contrast below and lateral to the coracoid process 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. [4]

MRI with surface coils is used to image the shoulder joint. [4]

Additional images

See also

Related Research Articles

<span class="mw-page-title-main">Scapula</span> Bone that connects the humerus (upper arm bone) with the clavicle (collar bone)

The scapula, also known as the shoulder blade, is the bone that connects the humerus with the clavicle. 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.

<span class="mw-page-title-main">Humerus</span> Long bone of the upper arm

The humerus 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 of a rounded head, a narrow neck, and two short processes. The body is cylindrical in its upper portion, and more prismatic below. The lower extremity consists of 2 epicondyles, 2 processes, and 3 fossae. As well as its true anatomical neck, the constriction below the greater and lesser tubercles of the humerus is referred to as its surgical neck due to its tendency to fracture, thus often becoming the focus of surgeons.

<span class="mw-page-title-main">Rotator cuff</span> Group of muscles

The rotator cuff 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 are:

<span class="mw-page-title-main">Latissimus dorsi muscle</span> Large, flat back muscle

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.

<span class="mw-page-title-main">Shoulder</span> Part of the body

The human shoulder is made up of three bones: the clavicle (collarbone), the scapula, and the humerus as well as associated muscles, ligaments and tendons.

<span class="mw-page-title-main">Deltoid muscle</span> Shoulder muscle

The deltoid muscle is the muscle forming the rounded contour of the 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 of three distinct sets of muscle fibers, namely the

  1. anterior or clavicular part
  2. posterior or scapular part
  3. intermediate or acromial part
<span class="mw-page-title-main">Upper limb</span> Consists of the arm, forearm, and hand

The upper limbs or upper extremities are the forelimbs of an upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digits, including all the musculatures and ligaments involved with the shoulder, elbow, wrist and knuckle joints. In humans, each upper limb is divided into the shoulder, arm, elbow, forearm, wrist and hand, and is primarily used for climbing, lifting and manipulating objects. In anatomy, just as arm refers to the upper arm, leg refers to the lower leg.

<span class="mw-page-title-main">Teres minor muscle</span> Muscle of the rotator cuff

The teres minor is a narrow, elongated muscle of the rotator cuff. The muscle originates from the lateral border and adjacent posterior surface of the corresponding right or left scapula and inserts at both the greater tubercle of the humerus and the posterior surface of the joint capsule.

<span class="mw-page-title-main">Triceps</span> Muscle on the back of the upper arm

The triceps, or triceps brachii, is a large muscle on the back of the upper limb of many vertebrates. It consists of three parts: the medial, lateral, and long head. It is the muscle principally responsible for extension of the elbow joint.

<span class="mw-page-title-main">Acromioclavicular joint</span> Shoulder junction between the scapula and the clavicle

The acromioclavicular joint, or AC joint, is a joint at the top of the shoulder. It is the junction between the acromion and the clavicle. It is a plane synovial joint.

<span class="mw-page-title-main">Infraspinatus muscle</span> Main external rotator of the shoulder

In human anatomy, the infraspinatus muscle is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa. As one of the four muscles of the rotator cuff, the main function of the infraspinatus is to externally rotate the humerus and stabilize the shoulder joint.

<span class="mw-page-title-main">Subscapularis muscle</span> Large triangle muscle of the shoulder

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.

<span class="mw-page-title-main">Teres major muscle</span> Muscle of the upper limb

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.

<span class="mw-page-title-main">Shoulder girdle</span> Set of bones which connects the arm to the axial skeleton on each side

The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans, it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of the clavicle, scapula, and coracoid. Some mammalian species have only the scapula.

<span class="mw-page-title-main">Glenoid fossa</span> Part of the shoulder

The glenoid fossa of the scapula or the glenoid cavity is a bone part of the shoulder. The word glenoid is pronounced or and is from Greek: gléne, "socket", reflecting the shoulder joint's ball-and-socket form. It 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.

<span class="mw-page-title-main">Coracoacromial ligament</span> Ligament between the coracoid process and the acromion of the scapula

The coracoacromial ligament is a strong triangular ligament between the coracoid process and the acromion. It protects the head of the humerus. Its acromial attachment may be repositioned to the clavicle during reconstructive surgery of the acromioclavicular joint.

<span class="mw-page-title-main">Glenohumeral ligaments</span> Ligaments of the shoulder

In human anatomy, the glenohumeral ligaments (GHL) are three ligaments on the anterior side of the glenohumeral joint. Reinforcing the anterior glenohumeral joint capsule, the superior, middle, and inferior glenohumeral ligaments play different roles in the stability of the head of the humerus depending on arm position and degree of rotation.

The scapulohumeral muscles are a group of seven muscles that connect the humerus to the scapula. They are amongst the muscles that act on and stabilise the glenohumeral joint in the human body.

<span class="mw-page-title-main">Capsule of the glenohumeral joint</span> Articular capsule of the shoulder joint

The capsule of the glenohumeral (shoulder) joint is the articular capsule of the shoulder. It completely surrounds the joint. It is attached above to the circumference of the glenoid cavity beyond the glenoidal labrum, and below to the anatomical neck of the humerus, approaching nearer to the articular cartilage above than in the rest of its extent.

<span class="mw-page-title-main">Shoulder impingement syndrome</span> Medical condition

Shoulder impingement syndrome is a syndrome involving tendonitis of the rotator cuff muscles as they pass through the subacromial space, the passage beneath the acromion. It is particularly associated with tendonitis of the supraspinatus muscle. This can result in pain, weakness, and loss of movement at the shoulder.

References

  1. "Glenohumeral joint space". radref.org., in turn citing: Petersson CJ, Redlund-Johnell I (April 1983). "Joint space in normal gleno-humeral radiographs". Acta Orthopaedica Scandinavica. 54 (2): 274–276. doi: 10.3109/17453678308996569 . PMID   6846006.
  2. 1 2 Petersson CJ, Redlund-Johnell I (February 1984). "The subacromial space in normal shoulder radiographs". Acta Orthopaedica Scandinavica. 55 (1): 57–58. doi:10.3109/17453678408992312. PMID   6702430.
  3. Kadi R, Milants A, Shahabpour M (December 2017). "Shoulder Anatomy and Normal Variants". Journal of the Belgian Society of Radiology. 101 (Suppl 2): 3. doi: 10.5334/jbr-btr.1467 . PMC   6251069 . PMID   30498801.
  4. 1 2 3 4 5 6 7 8 Ryan, Stephanie (2011). "Chapter 7". Anatomy for diagnostic imaging (Third ed.). Elsevier Ltd. p. 258, 260. ISBN   9780702029714.
  5. 1 2 Saladin KS (2012). Anatomy & Physiology: The Unity of Form and Function (Sixth ed.). New York, NY: McGraw-Hill.
  6. Chang, Lou-Ren; Anand, Prashanth; Varacallo, Matthew (2024), "Anatomy, Shoulder and Upper Limb, Glenohumeral Joint", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID   30725703 , retrieved 7 August 2024
  7. Moore K, Dalley A, Agur A (2014). Moore Clinically Oriented Anatomy (7th ed.). Lippincott Williams and Wilkins.
  8. "Shoulder Pain: Raising the level of diagnostic certainty about SLAP lesions". Clinical Updates for Medical Professionals. Mayo Clinic. 5 September 2012. Retrieved 2 December 2015.
  9. Rapariz, Jose M.; Martin-Martin, Silvia; Pareja-Bezares, Antonio; Ortega-Klein, Jose (2010). "Shoulder dislocation in patients older than 60 years of age". International Journal of Shoulder Surgery. 4 (4): 88–92. doi: 10.4103/0973-6042.79792 . ISSN   0973-6042. PMC   3100813 . PMID   21655003.
  10. Saladin K (2015). Anatomy & Physiology: The Unity of Form and Function (Seventh ed.). McGraw-Hill Education. p. 296.