Four muscles whose initials spell SITS
Rotator cuff — supraspinatus, infraspinatus, teres minor, subscapularis.
Anatomy · Joints & cartilage
Rotator cuff
Four muscles: SITS
Upper limb · scapula to humerus
The rotator cuff is the group of four muscles, supraspinatus, infraspinatus, teres minor and subscapularis, whose tendons fuse with the capsule of the shoulder joint and form a cuff around the head of the humerus. They rotate the arm and, more importantly, hold the humeral head firmly in the shallow glenoid cavity. Supraspinatus is the one most often torn.
How to spot them
- ▸Four muscles arising from the scapula and inserting on the tubercles of the humerus: the acronym SITS
- ▸Supraspinatus, infraspinatus and teres minor insert on the greater tubercle; subscapularis on the lesser
- ▸Teres major is not part of it, despite the similar name
- ▸The subacromial bursa lies between the cuff and the acromion above
What to know
Their tendons blend with the capsule of a ball-and-socket joint and press the ball into a shallow socket
Rotator cuff — the dynamic stabiliser of the glenohumeral joint.
The one from above the scapular spine that initiates abduction of the arm is also the one most often torn
Rotator cuff — supraspinatus, tested by the 'empty can' test.
The only medial rotator among the four lies on the front of the scapula, against the ribs
Rotator cuff — subscapularis.
Squeezed under the acromion as the arm is raised, causing a painful arc between about 60 and 120 degrees
Rotator cuff — subacromial impingement.
Key ideas
- SITS: Supraspinatus (abducts), Infraspinatus and Teres minor (lateral rotation), Subscapularis (medial rotation).
- The cuff is the joint's real stabiliser: the shoulder's shallow socket and loose capsule have little else.
Quick-fire facts
- •OpenStax: the thickening of the capsule formed by the fusion of the four muscle tendons is called the rotator cuff; it holds the head of the humerus within the glenoid cavity.
- •Nerves: suprascapular nerve to supraspinatus and infraspinatus; axillary nerve to teres minor; upper and lower subscapular nerves to subscapularis.
- •Supraspinatus tendon is the most commonly torn, especially where it passes under the acromion.
- •Teres major is not a rotator cuff muscle: it is a medial rotator lying just below teres minor.
- •Injury is common in overhead sports (throwing, swimming, racquet sports) and with age.
- •Rotator cuff tears may be seen on ultrasound or MRI.
- •The 'painful arc' between about 60 and 120 degrees of abduction points to impingement.
Drill it — 7 cards
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