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 fibers of deltoid, coracobrachialis, biceps brachii
  • extension: posterior fibers 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
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:

Venous drainage

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

Innervation