(View in the front)(like you put your hand on someone’s shoulder from the back)

• Supraspinatus (suprascapular nerve)
  • Abducts arm initially (before the action of the deltoid)
  • Most common rotator cuff injury (trauma or degeneration and impingement leading to tendinopathy or tear)
  • Assessed by the “empty/full can” test
• Infraspinatus (suprascapular nerve)
  • Externally rotates arm
  • The only one of these four muscles that does not participate in abduction.
  • Common pitching injury
• Teres minor (axillary nerve)
  • Adducts and externally rotates arm
• Subscapularis (upper and lower subscapular nerves)
  • Internally rotates and adducts arm

Abduction of the upper limb

• (0°-15°) Abduction of the upper extremity is initiated by the supraspinatus muscle (suprascapular nerve).
• (15°-110°) Further abduction to the horizontal position is a function of the deltoid muscle (axillary nerve).
• (110°-180°) Raising the extremity above the horizontal position requires scapular rotation by action of the trapezius (accessory nerve CN XI) and serratus anterior (long thoracic nerve).