Rotator Cuff Muscles: Functions, Tears, and Clinical Examination
A clinical anatomy reference for the four rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis) — origins, insertions, actions, tear patterns, and the physical examination tests used to diagnose each.
Learning Objectives
- ✓Identify the four rotator cuff muscles, their origins, insertions, and innervation.
- ✓Recognize tear patterns and clinical presentations for each muscle.
- ✓Apply specific physical examination tests to localize rotator cuff pathology.
1. Direct Answer: The Four Rotator Cuff Muscles
The rotator cuff consists of four muscles whose tendons blend into a continuous cuff surrounding the glenohumeral joint: SUPRASPINATUS (initiates abduction 0-15°, innervated by suprascapular nerve from C5/C6), INFRASPINATUS (external rotation, suprascapular nerve C5/C6), TERES MINOR (external rotation, axillary nerve C5/C6), and SUBSCAPULARIS (internal rotation, upper and lower subscapular nerves C5/C6). Together they stabilize the humeral head in the glenoid fossa during all shoulder movements and contribute to specific rotational and abduction movements. The mnemonic SITS (Supraspinatus, Infraspinatus, Teres minor, Subscapularis) captures all four. Supraspinatus is by far the most commonly torn — its tendon passes under the acromion in a tight space subject to impingement.
Key Points
- •Four muscles: SITS (Supraspinatus, Infraspinatus, Teres minor, Subscapularis).
- •Three external rotators (Supra, Infra, Teres minor) + one internal rotator (Subscap).
- •All originate from the scapula and insert on the humerus.
- •Supraspinatus is the most commonly torn.
2. Supraspinatus: Anatomy, Function, and Tears
Origin: supraspinous fossa of the scapula. Insertion: greater tubercle of the humerus (superior facet). Action: initiates the first 15° of abduction; deltoid takes over thereafter. Innervation: suprascapular nerve (C5/C6). The tendon passes through the subacromial space (under the coracoacromial arch) and is the most commonly torn rotator cuff tendon. Repetitive overhead activity (painters, swimmers, baseball pitchers) and age-related degeneration are the leading causes. Acute tears in young patients are typically traumatic (fall on outstretched arm); chronic tears in older patients are degenerative. Clinical presentation: weakness initiating abduction, pain over the lateral upper arm (referred), positive empty can test, positive Jobe test.
Key Points
- •Origin: supraspinous fossa. Insertion: greater tubercle (superior facet).
- •Action: initiates first 15° of abduction.
- •Most commonly torn rotator cuff tendon.
- •Subacromial space narrow → prone to impingement and degeneration.
3. Infraspinatus and Teres Minor: External Rotators
INFRASPINATUS: origin infraspinous fossa, insertion greater tubercle (middle facet), action external rotation of shoulder, innervation suprascapular nerve (C5/C6). TERES MINOR: origin lateral border of scapula, insertion greater tubercle (inferior facet), action external rotation, innervation axillary nerve (C5/C6). Together they are the primary external rotators of the shoulder. Isolated infraspinatus weakness produces external rotation weakness in adduction; teres minor weakness shows up better in external rotation at 90° abduction. Clinical: Hornblower's sign (inability to maintain external rotation at 90° abduction) tests teres minor; external rotation lag sign tests both. Infraspinatus tears often accompany supraspinatus tears in larger cuff defects.
Key Points
- •Both external rotators of the shoulder.
- •Infraspinatus tested in adduction; teres minor tested at 90° abduction.
- •Hornblower sign: teres minor weakness.
- •External rotation lag sign: combined Supra/Infra weakness.
4. Subscapularis: The Anterior Cuff
Origin: subscapular fossa (anterior surface of the scapula). Insertion: lesser tubercle of the humerus. Action: internal rotation of the shoulder. Innervation: upper and lower subscapular nerves (C5/C6/C7). Tears of subscapularis are less common than other cuff tears but often missed clinically — patients present with vague anterior shoulder pain rather than the classic posterior weakness of other cuff tears. Tests: lift-off test (Gerber's test) — patient places hand on lower back and attempts to lift it away from the body; inability indicates subscapularis weakness. Belly-press test — patient presses on the belly with the hand and elbow forward; elbow falling backward indicates subscapularis weakness. Subscapularis tears are often associated with anterior shoulder dislocation.
Key Points
- •Internal rotator; origin subscapular fossa, insertion lesser tubercle.
- •Often-missed cause of anterior shoulder pain.
- •Lift-off test (Gerber) and belly-press test diagnose.
- •Association with anterior shoulder dislocation.
5. Physical Examination Tests Summary
EMPTY CAN / JOBE TEST: shoulder abducted 90°, thumbs pointing down, patient resists downward pressure — pain or weakness indicates supraspinatus pathology. HAWKINS TEST: shoulder forward-flexed 90° with elbow flexed 90°, internal rotation — pain indicates subacromial impingement. NEER TEST: passive forward flexion of arm in internal rotation — pain indicates subacromial impingement. DROP ARM TEST: arm passively abducted to 90°, patient asked to slowly lower — inability or pain indicates large supraspinatus tear. EXTERNAL ROTATION RESISTANCE: tests infraspinatus/teres minor. LIFT-OFF TEST: hand on lower back, lift away from body — subscapularis. BELLY-PRESS TEST: press on belly with hand and elbow forward — subscapularis. Imaging (MRI) confirms tear pattern and grading; ultrasound is also widely used for dynamic assessment.
Key Points
- •Empty can / Jobe: supraspinatus.
- •Hawkins / Neer: subacromial impingement.
- •Drop arm: large supraspinatus tear.
- •External rotation resistance: infraspinatus / teres minor.
- •Lift-off / belly-press: subscapularis.
6. Tear Patterns and Treatment
Cuff tears are described by SIZE (small <1 cm, medium 1-3 cm, large 3-5 cm, massive >5 cm) and DEPTH (partial-thickness articular vs bursal vs intratendinous, vs full-thickness). They are also described by which tendons are involved (isolated supraspinatus, supra + infra, etc.). Treatment depends on age, activity level, tear size, and chronicity. Conservative treatment (PT, NSAIDs, corticosteroid injection) is first-line for partial tears, low-demand patients, and chronic asymptomatic tears. Surgical repair (arthroscopic or open) is considered for acute full-thickness tears in active patients, large tears, and tears failing conservative management. Massive irreparable tears may require reverse total shoulder arthroplasty in older patients with rotator cuff arthropathy.
Key Points
- •Size: small <1cm, medium 1-3cm, large 3-5cm, massive >5cm.
- •Depth: partial vs full thickness.
- •Conservative first for partial tears and low-demand patients.
- •Surgical repair for acute full-thickness in active patients.
- •Massive irreparable: reverse total shoulder arthroplasty.
7. Using AnatomyIQ for Rotator Cuff Practice
Snap a photo of any clinical vignette or imaging study and AnatomyIQ identifies the rotator cuff muscle involved, walks through the relevant physical exam tests, and predicts the most likely tear pattern. The app produces practice cases at three difficulty levels with anatomical diagrams. This content is for educational purposes only and does not constitute medical advice.
Key Points
- •Vignette to anatomy mapping.
- •Exam test recommendations based on suspected muscle.
- •Practice cases at multiple difficulty levels.
High-Yield Facts
- ★SITS: Supraspinatus, Infraspinatus, Teres minor, Subscapularis.
- ★Supraspinatus: initiates 0-15° abduction; most commonly torn.
- ★Infraspinatus + Teres minor: external rotation.
- ★Subscapularis: internal rotation; lift-off and belly-press tests.
- ★Jobe (empty can) test: supraspinatus pathology.
- ★Suprascapular nerve innervates supraspinatus AND infraspinatus.
Practice Questions
1. A baseball pitcher has weakness initiating shoulder abduction and pain over the lateral arm. Most likely diagnosis and test?
2. A patient cannot lift their hand off their lower back. Which muscle?
3. A patient with shoulder pain has weakness in external rotation at 90° abduction (Hornblower sign). Which muscle?
FAQs
Common questions about this topic
The supraspinatus tendon passes through the subacromial space — a narrow tunnel between the acromion above and humeral head below. Repetitive overhead motion compresses the tendon against the underside of the acromion (impingement), gradually weakening it. Age-related degeneration of the tendon itself adds vulnerability. Combined, these factors make supraspinatus tears the most common rotator cuff pathology.
Impingement is inflammation and irritation of the cuff tendons (especially supraspinatus) as they pass under the acromion — Hawkins and Neer tests positive, pain with overhead motion, but no structural tear. A cuff TEAR is a structural defect in the tendon — diagnosed by weakness on muscle-specific tests (Jobe, lift-off) and confirmed on imaging. Impingement can progress to a tear over time if untreated.
Acute full-thickness tears in active patients (especially under 60), tears causing significant weakness or disability, tears failing 3-6 months of conservative management, and partial tears progressing to full-thickness. Conservative management (PT, NSAIDs, corticosteroid injection) is first-line for partial tears, asymptomatic tears found incidentally, and low-demand patients.
Compensatory mechanisms — the deltoid and intact cuff muscles can substitute for a torn muscle, especially if the tear developed gradually. Imaging studies of asymptomatic older adults find a substantial percentage have full-thickness tears without pain or functional limitation. This is one reason MRI findings must be correlated with clinical examination, not treated in isolation.
Snap a photo of a clinical vignette or imaging study and AnatomyIQ identifies the muscle involved, recommends the relevant physical exam tests, and predicts the most likely tear pattern. Practice cases come in three difficulty levels. This content is for educational purposes only.