| Shoulder joint | |
|---|---|
 Cross-section of shoulder joint | |
| Details | |
| Identifiers | |
| Latin | articulatio humeri |
| MeSH | D012785 |
| TA98 | A03.5.08.001 |
| TA2 | 1764 |
| FMA | 25912 |
| Anatomical terminology | |
Theshoulder joint (orglenohumeral joint from Greekglene, eyeball, + -oid, 'form of', + Latinhumerus,shoulder) is structurally classified as asynovialball-and-socket joint and functionally as a diarthrosis and multiaxial joint. It involves an articulation between theglenoid fossa of thescapula (shoulder blade) and the head of thehumerus (upper arm bone). Due to the very loosejoint capsule, it gives a limited interface of the humerus and scapula, it is the most mobile joint of the human body.
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 theglenoid labrum. The glenoid labrum is a ring ofcartilaginous fibre attached to the circumference of the cavity. This ring is continuous with thetendon of thebiceps brachii above.
Significant joint spaces are:
Theaxillary space is ananatomic space between the associated muscles of the shoulder. This space transmits thesubscapular artery and theaxillary nerve.
The shoulder joint has a very loosejoint capsule, which can sometimes predispose the shoulder todislocate.[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 tosupraglenoid tubercle.[4]
A number of small fluid-filled sacs known assynovial bursae are located around the capsule to aid mobility:
Thesupra-acromial bursa does not normally communicate with the shoulder joint.
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 therotator 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 thebicipital groove on the humerus and inserts on the superior margin of the glenoid cavity to press thehead of the humerus against the glenoid cavity.[5] Other long muscles such aspectoralis major,latissimus dorsi,teres major anddeltoid muscles also provide support to the shoulder joint.[4]
The tendons of the rotator cuff and their respective muscles (supraspinatus muscle,infraspinatus,teres minor, andsubscapularis) stabilize and fix the joint.[4] The supraspinatus, infraspinatus and teres minor muscles aid in abduction and external rotation.[6]
The nerves supplying the shoulder joint all arise in thebrachial plexus. They are thesuprascapular nerve, theaxillary nerve and thelateral pectoral nerve.
The shoulder joint is supplied with blood by branches of theanterior andposterior circumflex humeral arteries, thesuprascapular artery and thescapular circumflex artery.
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Therotator cuff muscles of the shoulder produce a hightensile force, and help to pull the head of the humerus into the glenoid cavity.
The glenoid cavity is shallow and contains theglenoid labrum which deepens it and aids stability. With 120 degrees of unassisted flexion, the shoulder joint is the most mobile joint in the body.
The movement of the scapula across therib cage in relation to the humerus is known as thescapulohumeral 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 largetrapezius 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.
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 asfrozen shoulder or adhesive capsulitis.
ASLAP 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 byinflammation which often presents a set of symptoms known assubacromial impingement.
Arthrography of shoulder joint (with or withoutcomputed tomography) is performed by injecting contrast below and lateral to thecoracoid 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 entersubacromial bursa unless supraspinatus tendon is completely ruptured.[4]
MRI with surface coils is used to image the shoulder joint.[4]
