Shoulder

Simply put, the shoulder, or shoulder joint, is the connection of the upper arm and the thorax. Comprising of numerous ligamentous and muscular structures, the only actual bony articulations are the glenohumeral joint and the acromioclavicular joint (ACJ). The shoulder allows for a large range of motion, but is also more prone to dislocation and other injuries.

Gross anatomy

Location

The glenoid fossa of the scapula articulates with the anatomical head of the humerus as a synovial ball and socket joint. The glenoid fossa is deepened by the glenoid labrum.

The joint capsule attaches proximal to the glenoid fossa and attaches further distally to the anatomical neck of the humerus. The capsule is looser inferiorly to allow for tightening during abduction.

Movements

• flexion: anterior fibres of deltoid, coracobrachialis, biceps brachii
• extension: posterior fibres of deltoid, teres minor, teres major
• abduction: supraspinatus, deltoid, trapezius
• adduction: pectoralis major, subscapularis, teres major, latissimus dorsi
• internal rotation: teres major, latissimus dorsi, pectoralis major
• external rotation: infraspinatus, teres minor

Bursae

Numerous bursae are associated with the shoulder joint, which include the subacromial-subdeltoid and subcoracoid bursae.

Ligaments

• superior, middle and inferior glenohumeral ligaments, from their attachments along the anterior surface of the glenoid fossa extending further inferiorly
• transverse humeral ligament (holds long head of biceps down as it runs in the intertubercular groove)
• coracohumeral ligament
• long head of biceps (from supraglenoid tubercle) is intracapsular, running in the superior portion of the joint
• long head of triceps at its origin (from infraglenoid tubercle) also supports the joint inferiorly
• also reinforced by important extrinsic ligaments including the acromioclavicular, coracoacromial and coracoclavicular ligaments

Tendons

The shoulder joint is reinforced by the rotator cuff muscles/tendons:

• supraspinatus: from supraspinous fossa to superior facet on greater tubercle
• infraspinatus: from infraspinous fossa to middle facet on greater tubercle
• teres minor: from inferolateral border of the scapula to the inferior facet on the greater tubercle
• subscapularis: from the subscapular fossa to the lesser tubercle

Arterial supply

Arterial supply is from the branches of the scapular anastomosis but primarily from the axillary artery:

• suprascapular artery
• circumflex scapular artery
• anterior and posterior circumflex humeral arteries

Venous drainage

Veins with corresponding names, accompany the arteries, and drain the shoulder via a periscapular venous plexus.

Innervation

Multiple articular branches are derived from several nerves (Hilton's law):

• suprascapular nerve
• lateral pectoral nerve
• axillary nerve

Related pathology

• signs
  • geyser sign
  • cheerio sign
• traumatic
  • anterior shoulder dislocation
  • posterior shoulder dislocation
  • inferior shoulder dislocation
  • pseudodislocation of the shoulder
  • Bennett lesions of the shoulder
  • little league shoulder
  • anterior glenolabral injuries
    • Bankart lesion
    • bony Bankart lesion
    • anterior labroligamentous periosteal sleeve avulsion (ALPSA)
    • Perthes lesion
    • glenolabral articular disruption (GLAD)
    • humeral avulsion of the glenohumeral ligament (HAGL)
    • bony humeral avulsion of the glenohumeral ligament (BHAGL)
  • posterior glenolabral injuries
    • reverse Bankart lesion
    • POLPSA lesion
    • Kim lesion
  • humeral head injuries
    • Hill-Sachs lesion
    • Reverse Hill-Sachs lesiondefect - McLaughlin(McLaughlin lesion)
• metabolic
  • Milwaukee shoulder
• degenerative
  • Charcot joint
• others
  • adhesive capsulitis of the shoulder - frozen (frozen shoulder)
  • subacromial impingement
  • subcoracoid impingement
  • posterosuperior impingement
  • anterosuperior inner impingement
  • glenoid retroversion