Shoulder ultrasound is one of the most requested MSK studies, and for good reason — it's faster than MRI, dynamic, and when done well, accurate for full-thickness rotator cuff tears. The key is a systematic approach so nothing is missed.

Why Ultrasound for the Shoulder?

Real-time dynamic assessment — elevate the arm, compare sides during movement
Detects full-thickness tears with sensitivity > 90%, specificity > 95%
Partial-thickness tears: sensitivity ~70–80% (MRI is better for deep partial tears)
No claustrophobia, no contrast, no radiation
Immediate clinical correlation — the patient can point to where it hurts

What ultrasound is NOT great at: labral pathology (requires MRI arthrogram), glenohumeral joint pathology deep to the joint.

Patient Position and Setup

Position: Patient seated on a stool or exam table with no backrest, arms at side. For different tendons, you'll reposition the arm.

Probe: 5–15 MHz linear transducer. High-frequency for superficial tendons.

Orientation: Keep your probe in a consistent orientation — anisotropy (tendon echogenicity changing with angle) is the biggest pitfall. Tendons must be imaged perpendicular to their fibers, or they'll falsely appear hypoechoic.

Rotator Cuff Tendons: Quick Anatomy

Four tendons form the cuff:

Supraspinatus (SS): Most common tear location — inserts on greater tuberosity, superior facet
Infraspinatus (IS): Posterior, inserts on greater tuberosity, middle facet
Subscapularis (Sub): Anterior, inserts on lesser tuberosity — often missed
Teres minor: Inferior, rarely torn in isolation

The interval: Between supraspinatus (anterior) and subscapularis (medial) is the rotator interval — contains the biceps tendon, coracohumeral ligament.

Scanning Protocol

1. Biceps Tendon (Start Here — Your Landmark)

Position: Elbow flexed 90°, forearm supinated, arm at side — "Popeye position."

Probe placement: Transverse across the bicipital groove (anterior shoulder).

Normal appearance:

Round, oval hyperechoic tendon within the groove
Surrounded by a small amount of fluid (≤ 3 mm is normal)
Echogenic peritenon

Pathology:

Tenosynovitis: Fluid around the tendon > 3 mm, or anechoic rim
Tendinosis: Heterogeneous, thickened tendon, loss of fibrillar pattern
Tear/subluxation: Absent tendon in groove (full rupture) or tendon medially displaced

Scan in long axis (probe rotated 90°): Normal tendon shows linear fibrillar pattern.

2. Subscapularis Tendon

Position: Externally rotate the arm (hand facing outward, elbow flexed).

Probe placement: Transverse across the anterior shoulder, medial to the biceps groove.

Normal: Hyperechoic, striated (multipennate) tendon inserting on the lesser tuberosity. The subscapularis has multiple slips — looks "striped."

Pathology:

Partial tear (upper slip): focal hypoechoic defect at the superior border
Full-thickness tear: absent tendon, humeral head uncovered
The biceps may sublux medially over the subscapularis tear

3. Supraspinatus Tendon — The Critical Structure

Position: Extend the arm behind the back (modified Crass position) — patient places hand on posterior iliac crest, thumb pointing posteriorly. This rotates the supraspinatus anteriorly and out from under the acromion.

Probe placement: Coronal oblique across the anterior shoulder, parallel to the tendon fibers.

Normal appearance:

Hyperechoic, convex "beak" shape overlying the humeral head
Uniform echogenicity
Thickness: 5–8 mm at the critical zone (1 cm from insertion)

Pitfall — anisotropy: The tendon's echogenicity changes dramatically if you angle the probe even slightly. Always rock the probe to find the brightest (most perpendicular) angle before interpreting.

Tear findings:

Finding	Appearance
Full-thickness tear	Focal hypoechoic or anechoic defect through the full tendon thickness; "naked" humeral head; cortical irregularity
Partial articular-side tear	Hypoechoic defect at the deep (articular) surface of the tendon
Partial bursal-side tear	Hypoechoic defect at the superficial (bursal) surface
Tendinosis	Diffuse thickening, heterogeneity, no discrete defect

Dynamic assessment: In real-time, advance the probe as the patient slowly lowers their arm from the Crass position. Watch the supraspinatus pass beneath the acromion — impingement shows as tendon catching or bunching under the acromion.

4. Infraspinatus Tendon

Position: Arm at side, forearm resting on lap.

Probe placement: Posterior shoulder, probe in long axis parallel to the scapular spine.

Normal: Hyperechoic, fibrillar tendon inserting on the greater tuberosity (middle facet). Slightly thinner than supraspinatus.

Pathology: Tears less common than supraspinatus; posterior approach helps. Look for focal hypoechoic defects at the insertion.

5. Subacromial-Subdeltoid Bursa

The bursa lies between the deltoid/acromion (superficial) and the rotator cuff (deep). It's the single largest bursa in the body.

Normal: Thin hypoechoic line ≤ 2 mm overlying the supraspinatus.

Bursitis: Distended, anechoic or complex fluid collection. Measure thickness.

Subacromial impingement: Dynamic assessment — watch the bursa compress or the supraspinatus bunch as the arm is elevated.

6. Acromioclavicular (AC) Joint

Position: Probe transverse across the AC joint (palpate the bony step at the top of the shoulder).

Normal: Joint space < 3 mm; smooth cortical surfaces; fibrocartilaginous disc may be visible.

Pathology: Joint space widening, osteophytes, distal clavicular erosion, effusion, AC separation (compare to contralateral side and stress views if requested).

Key Images to Capture

Biceps tendon — transverse (short axis)
Biceps tendon — longitudinal (long axis)
Subscapularis — transverse and long axis
Supraspinatus — long axis (Crass position)
Supraspinatus — short axis
Infraspinatus — long axis
Subacromial bursa — measure if thickened
AC joint — if clinically relevant
Any pathology — two planes with measurements

Common Pitfalls

Anisotropy: The #1 error. A normal tendon looks falsely torn if the probe isn't perpendicular to fibers. Rock the probe slightly — a real tear stays dark; anisotropy brightens with correct angulation.

Critical zone: The anterior supraspinatus 1 cm from insertion is the most common tear site — focus your attention here.

Missed subscapularis: This tendon is commonly skipped. Always scan it.

Equivocal findings: If you see a hypoechoic area you can't confidently classify, describe it precisely (location, dimensions, depth from surface) and note whether it involves the full thickness.

Reporting Language

Normal:

"Supraspinatus, infraspinatus, and subscapularis tendons intact bilaterally. No full-thickness rotator cuff tear. Subacromial-subdeltoid bursa not distended. Biceps tendon in normal position within the groove without peritendinous fluid."

Full-thickness tear:

"Full-thickness tear of the supraspinatus tendon with a focal hypoechoic defect measuring 1.8 cm in the anterior-posterior dimension at the critical zone near the greater tuberosity insertion. The humeral head cortex is visible through the defect. Recommend MRI for pre-operative planning."

Partial tear:

"Partial-thickness articular-surface tear of the supraspinatus tendon measuring approximately 0.7 cm in the AP dimension at the anterior insertion. No through-and-through defect. MRI is recommended for further characterization."

SonoBuddy's MSK protocols include shoulder, knee, and ankle scanning guides. Normal shoulder measurements are in the Measurements section.

Shoulder Ultrasound: Rotator Cuff, Biceps Tendon, and Subacromial Space