💪 Muscular System Lesson

SITS: the four rotator cuff muscles

One of the most tested muscle groups in all of anatomy — these four muscles stabilize the shoulder joint and are frequently injured.

Supraspin.

Infraspin.

Teres Min.

Subscap.

📖 Full Breakdown

Four muscles, four distinct actions, one commonly torn

All four attach to the humerus and work together to stabilize the glenohumeral (shoulder) joint during rotation.

Supraspinatus

Initiates abduction (0–15°)

The most commonly torn rotator cuff muscle — it gets compressed under the acromion during abduction, leading to the classic "painful arc" between 60-120° of shoulder abduction.

Infraspinatus

External rotation

Located on the posterior scapula, below the scapular spine.

Teres Minor

External rotation

Works alongside infraspinatus, positioned just below it.

Subscapularis

Internal rotation

The only rotator cuff muscle on the ANTERIOR scapula — all three other muscles are posterior, making subscapularis structurally and functionally distinct from the rest of the group.

🩺 Clinical / Exam Application

A patient reports shoulder pain specifically when raising their arm between 60 and 120 degrees, but not much pain below or above that range. This specific "painful arc" pattern is a classic sign of a supraspinatus tear — because supraspinatus is compressed under the acromion precisely within this range of motion, damage to this particular muscle produces pain localized to this exact arc, rather than throughout the entire range of shoulder movement.

⚠️ Exam Alert

The SITS acronym itself is frequently tested by name alone — expect exam questions to simply ask you to list the four rotator cuff muscles, since this specific group appears constantly across anatomy, physical therapy, and orthopedic exams.

🚧 Common Trap

Don't assume all four rotator cuff muscles are equally likely to tear. Supraspinatus is by far the most commonly injured due to its unique anatomical position under the acromion — the other three are comparatively far less frequently torn.

✅ Quick Check

Which rotator cuff muscle is the only one located on the anterior scapula, and what movement does it produce?

📝 Exam Prep

Common Exam Questions

❓ What is the rotator cuff and which muscle is most commonly injured?

✅ The rotator cuff is SITS: Supraspinatus, Infraspinatus, Teres Minor, and Subscapularis. These muscles stabilize the glenohumeral joint. The supraspinatus is most commonly torn since it gets compressed under the acromion during abduction, causing a painful arc between 60-120°.

❓ Which rotator cuff muscle is different from the other three, and how?

✅ Subscapularis is the only rotator cuff muscle located on the anterior scapula (the other three are posterior), and it is the only one that produces internal rotation rather than external rotation.