Rotator cuff
Cingulum musculotendineum rotatorum
Also known as: SITS muscles, musculotendinous cuff
Four scapulohumeral muscles (supraspinatus, infraspinatus, teres minor and subscapularis) whose tendons blend with the shoulder joint capsule. They hold the humeral head in the shallow glenoid and rotate the arm.
Overview
The glenohumeral joint gives up stability for mobility. Its large humeral head sits on a small, shallow glenoid, which the labrum deepens only slightly. Dynamic stability comes mainly from the rotator cuff. Its four tendons fuse with the capsule and form a musculotendinous cuff around the joint on its anterior, superior and posterior sides. Inferiorly there is no cuff, which is why most shoulder dislocations are anterior–inferior.
Throughout movement, the cuff compresses the humeral head into the glenoid and counteracts the upward shear of deltoid. This force-couple allows the head to rotate in place rather than ride up. Individually:
- Supraspinatus: initiates abduction.
- Infraspinatus and teres minor: lateral rotation.
- Subscapularis: medial rotation and anterior stability.
Supraspinatus, infraspinatus and teres minor insert in order on the superior, middle and inferior facets of the greater tubercle. Subscapularis inserts on the lesser tubercle.
- Location
Around the glenohumeral joint, beneath the deltoid and the coraco-acromial arch.
Parts & subdivisions
- Superior facet of the greater tubercle. Suprascapular nerve. Initiates abduction (0–15°).
- Middle facet. Suprascapular nerve. Lateral rotation.
- Inferior facet. Axillary nerve. Lateral rotation.
- Lesser tubercle. Upper and lower subscapular nerves. Medial rotation.
Anatomy
- Innervation
Suprascapular nerve (supraspinatus, infraspinatus), axillary nerve (teres minor), upper and lower subscapular nerves (subscapularis).
- Nerve roots
C5–C6
- Arterial supply
Suprascapular, circumflex scapular, posterior circumflex humeral and subscapular arteries.
- Relations
Deep to deltoid. The subacromial bursa separates supraspinatus from the acromion and the coraco-acromial ligament.
Function
- Holds the humeral head in the glenoid fossa (dynamic stability)
- Initiates abduction (supraspinatus)
- Lateral (infraspinatus, teres minor) and medial (subscapularis) rotation of the humerus
Clinical significance
Rotator cuff tear and impingement
Usually affects supraspinatus. Degeneration, plus impingement under the coraco-acromial arch, causes a painful arc (60–120°) and night pain. Full-thickness tears weaken abduction and external rotation (positive drop-arm test). The tear is confirmed by ultrasound or MRI.
Specific tests
Empty-can (Jobe): supraspinatus. External rotation lag / resisted ER: infraspinatus. Hornblower: teres minor. Lift-off / belly-press: subscapularis.
Mnemonics
SITS
Supraspinatus, Infraspinatus, Teres minor, Subscapularis. The first three ("SIT") insert on the greater tubercle from top to bottom. The last ("S") inserts on the lesser tubercle.
Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.