Rotator Cuff
The rotator cuff is a group of four muscles (supraspinatus, infraspinatus, teres minor, subscapularis) that stabilize the shoulder joint and rotate the arm. They are critical for shoulder function and commonly injured.
Origin, Insertion, Action, Innervation
OOrigin
Supraspinatus: Supraspinous fossa. Infraspinatus: Infraspinous fossa. Teres minor: Lateral border of scapula. Subscapularis: Subscapular fossa (anterior scapula).
IInsertion
Supraspinatus: Superior facet of greater tubercle. Infraspinatus: Middle facet of greater tubercle. Teres minor: Inferior facet of greater tubercle. Subscapularis: Lesser tubercle of humerus.
AAction
- • Supraspinatus: Initiates abduction (first 15°), stabilizes shoulder
- • Infraspinatus: Lateral rotation of the arm
- • Teres minor: Lateral rotation of the arm
- • Subscapularis: Medial rotation of the arm
NInnervation
Supraspinatus: Suprascapular nerve (C5, C6). Infraspinatus: Suprascapular nerve (C5, C6). Teres minor: Axillary nerve (C5, C6). Subscapularis: Upper and lower subscapular nerves (C5, C6).
Blood Supply
Suprascapular and subscapular arteries
Clinical Relevance
Rotator cuff tears are extremely common, especially supraspinatus, which is most vulnerable due to its position and blood supply. Impingement syndrome occurs when the cuff is compressed under the acromion. The 'empty can' test evaluates supraspinatus, while 'lift-off' test evaluates subscapularis.
Palpation
Supraspinatus can be palpated in the supraspinous fossa. Infraspinatus and teres minor on the posterior scapula. Subscapularis is deep and difficult to palpate directly.
Study Tips
- ✓SITS = Supraspinatus, Infraspinatus, Teres minor, Subscapularis
- ✓3 muscles insert on greater tubercle, 1 on lesser (Subscapularis)
- ✓Supraspinatus initiates abduction, deltoid continues it
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Common questions about the rotator cuff
The four rotator cuff muscles are Supraspinatus, Infraspinatus, Teres minor, and Subscapularis (remember: SITS). They surround the shoulder joint and work together to stabilize and move the arm.
The supraspinatus tendon passes through a narrow space under the acromion and has a relatively poor blood supply (watershed zone). Repeated overhead activities can cause impingement and degeneration, leading to tears.
The rotator cuff muscles stabilize the glenohumeral joint by holding the humeral head in the glenoid fossa. They also produce rotation of the arm: subscapularis medially rotates, while infraspinatus and teres minor laterally rotate.
The empty can test evaluates supraspinatus function. The patient holds their arms at 90° abduction in the scapular plane with thumbs pointing down (like emptying a can). Weakness or pain with downward resistance suggests supraspinatus pathology.