Anatomy of
the Shoulder

Anatomy of the Shoulder

The shoulder is a ball and socket joint. The ball is at the top of the upper arm bone (humerus) and the socket (glenoid) is part of the shoulder blade (scapula). When you lift your arm or reach overhead both parts of the joint are moving in a coordinated way to give you mobility. This is controlled by muscles.

Scapulohumeral Muscles

What are they? The rotator cuff, deltoid and teres major muscles.

What do they do? These muscles rotate the shoulder joint and lift the arm.

Rotator Cuff

What are they? The supraspinatus, infraspinatus, subscapularis and teres minor muscles.

What do they do?

  • Centre the ball of the shoulder in the socket during movement.
  • Rotate the shoulder to reach up behind our head and down behind our lower back.
  • Give us the ability to lift our arm above shoulder height.
  • Provide strength at shoulder height and overhead.

Scapulothoracic Muscles

What are they? These muscles include your upper, middle and lower trapezius muscles, the rhomboids, levator scapulae, serratus anterior and pectoralis minor muscles.

What do they do? These muscles control movement of the shoulder blade (scapula).

  • Move the shoulder joint as a whole up, down, forward and back e.g. when you shrug your shoulders up to your ears.
  • Move the shoulder blade when you lift your arm overhead.
  • Anchor and stabilize the shoulder blade against the rib cage when your use your arms in prolonged positions, with repetitive overhead activity or for powerful movements like pushing, pulling, lifting and throwing.

Working Together

The scapulothoracic and scapulohumeral muscles work in a coordinated way to create normal painfree movement at the shoulder joint. In addition, they provide stability to the shoulder joint while you move.

Many factors can contribute to shoulder pain and/or can alter how we move:

  • poor posture
  • muscle weakness
  • repetitive overhead movement
  • sustained postures or positioning
  • muscle or joint injury (rotator cuff tear, dislocation or fracture)
  • rheumatoid or osteoarthritis