Infraspinatus (Rotator Cuff)
Shoulder & Scapula · Upper Limb
The infraspinatus is a rotator cuff muscle occupying the infraspinous fossa on the posterior surface of the scapula, below the scapular spine. From this broad origin its fibres converge on the middle facet of the greater tubercle of the humerus. Its principal role is lateral (external) rotation of the arm, and, like the rest of the cuff, it constantly stabilises the glenohumeral joint by holding the humeral head snugly in its shallow socket. The infraspinatus is supplied by the suprascapular nerve (C5, C6), the same nerve that serves supraspinatus, so a lesion of this nerve can weaken both external rotation and the initiation of abduction.
Origin, Insertion, Action & Nerve
Origin
Infraspinous fossa of scapula
Insertion
Middle facet of greater tubercle of humerus
Action
Lateral (external) rotation of arm; stabilizes glenohumeral joint
Nerve
Suprascapular nerve (C5, C6)
Attachments explained
The Infraspinatus (Rotator Cuff) is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Infraspinous fossa of scapula
Insertion
Middle facet of greater tubercle of humerus
Action & function
When the Infraspinatus (Rotator Cuff) contracts, it produces the following movements: Lateral (external) rotation of arm; stabilizes glenohumeral joint.
As part of the Shoulder & Scapula group of the Upper Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Infraspinatus (Rotator Cuff) receives its nerve supply from the Suprascapular nerve (C5, C6). This nerve carries fibres from spinal segment(s) C5, C6.
Because a muscle can only contract when its nerve is intact, injury to the Suprascapular nerve or to its spinal roots (C5, C6) can weaken or paralyse the Infraspinatus (Rotator Cuff), impairing the movements it normally produces (lateral (external) rotation of arm). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Infraspinatus (Rotator Cuff) (the OIANS method)
Group the infraspinatus with teres minor as the pair of external rotators on the back of the shoulder. Because it fills the fossa below the scapular spine and pulls the greater tubercle backward, its action of lateral rotation follows logically from its posterior position. Feeling the muscle work when you rotate your forearm outward with the elbow tucked in makes the action concrete.
Remember its nerve by contrast: infraspinatus is driven by the suprascapular nerve, whereas its partner teres minor is driven by the axillary nerve. Holding those two facts side by side is a reliable way to avoid mixing up the external rotators on exams.
Frequently asked questions
Where is the Infraspinatus (Rotator Cuff) located?
The Infraspinatus (Rotator Cuff) is a muscle of the Shoulder & Scapula group, located in the Upper Limb.
What is the origin of the Infraspinatus (Rotator Cuff)?
Infraspinous fossa of scapula
What is the insertion of the Infraspinatus (Rotator Cuff)?
Middle facet of greater tubercle of humerus
What movements does the Infraspinatus (Rotator Cuff) produce?
Lateral (external) rotation of arm; stabilizes glenohumeral joint
What nerve supplies the Infraspinatus (Rotator Cuff)?
Suprascapular nerve (C5, C6)
Is the Infraspinatus (Rotator Cuff) free to study in OIANS?
Yes. The Infraspinatus (Rotator Cuff) is free in OIANS: its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory, and because it belongs to the Upper Limb it is also covered by the free Quiz and Flashcard decks. The other regions, the "All Muscles" deck, and the Progress and Explore tools are unlocked with a one-time Lifetime purchase.
Related muscles
Study the Infraspinatus (Rotator Cuff)
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