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The rotator cuff is a group of four muscles and their tendons that stabilize the glenohumeral (shoulder) joint and allow a wide range of arm movements. They dynamically maintain the humeral head within the glenoid fossa during motion.

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Rotator cuff muscles, which act to stabilise the shoulder joint. - TeachMeSeries Ltd (2024)

Anatomy

The four rotator cuff muscles are:

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Key relationship: The supraspinatus, infraspinatus, and teres minor insert on the greater tuberosity (posterior cuff), whereas the subscapularis inserts on the lesser tuberosity (anterior cuff).

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Muscle	Origin	Insertion	Action	Stabilizing action
Supraspinatus	‣: Posterior aspect, above scapular spine	‣: Greater tuberosity	Abduction:
0-15°: Primary muscle
15-90°: Assists the deltoid	Flexion
Extension
Infraspinatus	‣: Posterior aspect, below scapular spine	‣: Greater tuberosity	External rotation
Humeral head depressor	Flexion
Teres minor	‣: Lateral scapular border	‣: Greater tuberosity	External rotation
Subscapularis	‣: Anterior surface	‣: Lesser tuberosity	Internal rotation	External rotation
Extension

Radiology

https://www.youtube.com/watch?v=H91veR0dRfY

https://youtu.be/IiAZZOpBmH0

Impingement & Tears:

The rotator cuff tendons traverse a narrow space between the acromion/coracoacromial arch superiorly and the humeral head/greater tuberosity inferiorly, making them vulnerable to impingement and tears.

Supraspinatus is most commonly affected.
MRI is the modality of choice for tendon pathology (tendinosis, partial- or full-thickness tears).
MR arthrography helps detect partial-thickness articular surface tears by contrast leakage.

Degeneration & Atrophy:

Chronic tears lead to fatty infiltration and muscle atrophy, graded using the Goutallier classification (0 = normal, 4 = more fat than muscle). This strongly influences surgical prognosis.

Magic angle effect: