Infraspinatus muscle
Musculus infraspinatus
Infraspinatus is a thick rotator cuff muscle that fills the back of the shoulder blade below the spine and turns the arm outward.
At a glance
- English
- Infraspinatus muscle
- Latin (TA2)
- Musculus infraspinatus
- System
- Muscle
- Region
- Upper limb
- Side
- Paired, left and right
About the infraspinatus muscle
Infraspinatus is a broad, triangular muscle on the back of the scapula, occupying most of the hollow below the scapular spine. It is one of the four rotator cuff muscles that wrap the shoulder joint, and its tendon blends with the joint capsule as it passes over the back of the humeral head.
Its fibres arise from the inner two thirds of the infraspinous fossa and from the dense infraspinous fascia that covers the muscle. They converge laterally on a tendon that runs behind the shoulder joint, separated from the neck of the scapula by a small bursa in some people. It attaches to the middle impression on the humeral greater tubercle, between supraspinatus above and teres minor below. Deltoid and trapezius partly cover the muscle, and teres minor lies along its lower edge, often fused with it.
Infraspinatus is the main lateral rotator of the arm. As part of the cuff it also presses the humeral head into the shallow glenoid cavity and helps stop it gliding backward, keeping the joint stable when the arm is raised. Its nerve is the suprascapular nerve, which reaches the fossa by passing round the lateral edge of the scapular spine. Its blood comes from the suprascapular artery, which travels with the nerve, and from the circumflex scapular artery.
Because the suprascapular nerve turns round the spinoglenoid notch to reach this muscle, a cyst or a tight ligament at the notch can waste infraspinatus on its own, leaving supraspinatus intact. Tears of the rotator cuff may extend back into its tendon. Strength is checked by resisting outward rotation with the elbow at the side.
Attachments, action and supply
- Origin
- Inner two thirds of the scapular infraspinous fossa, plus the fascia covering it.
- Insertion
- Middle impression on the humeral greater tubercle, and the joint capsule.
- Action
- Laterally rotates the arm and helps hold the humeral head in the glenoid cavity.
- Nerve supply
- Suprascapular nerve (C5, C6).
- Blood supply
- Suprascapular and circumflex scapular arteries.
Anthromica
See the infraspinatus muscle where it really sits, with every layer of the body around it.
- Every layer, one body. Peel from muscle to bone, nerve, vessel and organ, and turn it any way.
- English and Latin. Every structure named the way your exam names it.
- Quiz until it sticks. Short drills on the structures you keep missing.
Free to start. No card.
