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Portrait of Infraspinatus

Anatomy · Muscles

Infraspinatus

Main lateral rotator of the arm

Upper limb · shoulder, rotator cuff

Infraspinatus is a thick triangular rotator cuff muscle filling the infraspinous fossa on the back of the scapula. It inserts on the middle facet of the greater tubercle and is the main lateral rotator of the arm. It is supplied by the suprascapular nerve.

How to spot them

  • ▸Fills the large triangular fossa below the spine of the shoulder blade
  • ▸Palpable through the skin below the scapular spine, partly under the deltoid and trapezius
  • ▸Lateral rotator, the counter to subscapularis on the front of the scapula
  • ▸Tendon is fused to the shoulder joint capsule as part of the rotator cuff

What to know

A rotator cuff muscle on the back of the shoulder blade, below the scapular spine

Infraspinatus.

The chief muscle that turns the arm outward, as when opening a door with the elbow at the side

Infraspinatus — lateral rotation of the arm.

Its tendon attaches to the middle facet of the greater tubercle of the humerus

Infraspinatus.

A muscle supplied by a nerve that winds round the spine of the scapula through the spinoglenoid notch

Infraspinatus — suprascapular nerve.

Its bulk lies in the infraspinous fossa, giving the back of the scapula its fullness

Infraspinatus.

Fibres run from the whole fossa up and out to a tendon that blends with the shoulder capsule

Infraspinatus.

Key ideas

  • Infraspinatus and teres minor together give lateral rotation and pull the humeral head down and back into the socket.
  • Wasting of the muscle in the fossa below the scapular spine suggests suprascapular nerve injury.

Quick-fire facts

  • •Origin: infraspinous fossa of the scapula and the infraspinous fascia.
  • •Insertion: middle facet of the greater tubercle of the humerus.
  • •Nerve supply: suprascapular nerve (C5–C6).
  • •Action: lateral rotation of the arm; stabilises the head of the humerus.
  • •It is a rotator cuff (SITS) muscle, alongside supraspinatus, teres minor and subscapularis.
  • •The suprascapular nerve reaches it round the spine of the scapula, through the spinoglenoid notch.
  • •Weakness of external rotation, with the elbow bent at the side, points to infraspinatus and teres minor.

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Sources