Shoulder ultrasound is a non-invasive, dynamic imaging tool used to assess muscle, tendon, and joint conditions in the shoulder. Because it captures live movement without radiation, it offers an efficient and patient-friendly way to diagnose common issues like rotator cuff tears, biceps tendinopathy, and subacromial bursitis.

1. Anatomy of the Shoulder Complex

The shoulder joint is a ball-and-socket joint formed by the head of the humerus and the glenoid cavity of the scapula (glenohumeral joint).

Bony Anatomy

Three primary bones meet at the shoulder complex to form the joint and its surrounding frame:

• Humerus: The head of the humerus forms the “ball” of the joint. It is rounded and significantly larger than the socket in which it rests.
• Scapula (Shoulder Blade): Contains a shallow socket (glenoid cavity) on its lateral border, along with two critical bony projections:
  • Acromion: A prominent arch at the top of the scapula that connects with the clavicle and sits over the joint.
  • Coracoid Process: A hook-like bony projection pointing anteriorly that serves as an attachment point for key muscles and ligaments.
• Clavicle (Collarbone): Anchors the shoulder assembly to the sternum, stabilizing the arm’s distance from the torso.

Joint Stability & Soft Tissue

Because the glenoid cavity covers less than one-third of the humeral head, soft tissue structures provide essential dynamic and static stability:

• Glenoid Labrum: A ring of fibrocartilage surrounding the rim of the shallow glenoid cavity. It deepens the socket by roughly 50% and provides a suction-cup effect to hold the humeral head in place.
• Articular Cartilage: Smooth hyaline cartilage covering both the humeral head and glenoid cavity to ensure low-friction gliding.
• Joint Capsule & Ligaments: Tough fibrous tissue enclosing the joint. Dynamic stabilizing ligaments include the superior, middle, and inferior glenohumeral ligaments, as well as the coracohumeral ligament.

Rotator Cuff Muscles

Dynamic stability during arm movement is provided by four deep muscles known collectively as the rotator cuff (SITS):

• Supraspinatus: Located superiorly and most commonly torn. Its tendon passes beneath the acromion to initiate arm abduction.
• Infraspinatus: Located posteriorly; externally rotates the shoulder.
• Teres Minor: Located posteriorly and inferior to the infraspinatus; externally rotates and adducts the arm.
• Subscapularis: Sits on the anterior face of the scapula and internally rotates the arm.

Other Important Sonographic Landmarks

• Biceps Tendon: Comprises the long head (LHBT) and short head. The long head travels through the bicipital groove, serving as a primary baseline landmark.
• Subacromial-Subdeltoid Bursa (SASD): A large bursa located between the rotator cuff tendons and the acromion/deltoid muscle that reduces friction during movement.
• Bony Landmarks: Acromion, greater tuberosity, lesser tuberosity, and the bicipital groove are critical for proper transducer positioning.

2. Indications for Shoulder Ultrasound

Shoulder ultrasound is specifically indicated for evaluating soft tissue pathology. Common clinical scenarios include:

• Pain and Tenderness: Unexplained shoulder pain, particularly over the lateral arm or anterior shoulder.
• Limited Range of Motion: Difficulty with overhead activities or reaching behind the back.
• Trauma or Overuse: Suspected rotator cuff tear (full or partial thickness), tendinosis, or tendon subluxation/dislocation.
• Impingement Syndrome: Clinical suspicion of subacromial impingement during active movement.
• Biceps Pathology: Suspected tenosynovitis, tendinosis, or rupture of the long head of the biceps tendon.
• Bursitis: Evaluation of fluid accumulation within the SASD bursa.
• Instability & Joint Effusion: Assessment of joint effusions and superficial labral changes (though MRI remains superior for intra-articular labral pathology).
• Guided Interventions: Aspiration of bursal fluid or calcifications, and therapeutic injections (e.g., corticosteroid into the SASD bursa).

3. Examination Protocol & Scanning Technique

A systematic and standardized approach is essential for a comprehensive examination. The patient is typically seated on a rotating stool facing the examiner. A high-frequency linear array transducer (7–15 MHz) is used for optimal superficial resolution.

1. Position 1: Long Head of Biceps Tendon (LHBT)

   • Positioning: Arm in neutral position, forearm resting on lap with palm up.
   • Technique: Place the transducer in the axial plane over the anterior shoulder to locate the bicipital groove. Evaluate the LHBT in both short-axis (axial) and long-axis (sagittal) planes to assess for tendinosis, tenosynovitis, and dislocation/subluxation.

2. Position 2: Subscapularis Tendon

   • Positioning: Arm externally rotated with elbow tucked at the side.
   • Technique: From Position 1, have the patient externally rotate the arm. Place the transducer axially and coronally to evaluate the subscapularis tendon insertion on the lesser tuberosity in short and long axes.

3. Position 3: Supraspinatus Tendon

   • Positioning: Hand on ipsilateral hip (Crass position) or behind the back (Modified Crass).
   • Technique: Positioning the hand on the lower back brings the supraspinatus out from beneath the acromion. Scan in the coronal and sagittal planes to evaluate the tendon from its insertion on the greater tuberosity to its musculotendinous junction.

4. Position 4: Infraspinatus, Teres Minor, & Posterior Labrum

   • Positioning: Arm adducted across the chest with hand on opposite shoulder.
   • Technique: Place the transducer on the posterior aspect of the shoulder below the spine of the scapula. Scan axially and coronally to visualize the infraspinatus, teres minor, posterior joint capsule, and posterior labrum.

Note: Dynamic imaging during active or passive movement should be performed throughout the scan to assess for subacromial impingement and tendon instability.

4. Normal Sonographic Appearance

Structure	Sonographic Appearance
Tendons (Rotator Cuff & Biceps)	Compact, hyperechoic (bright) parallel lines demonstrating a distinct fibrillar pattern. The supraspinatus has a smooth, convex superior contour.
Subacromial Bursa (SASD)	Thin, hyperechoic line between the cuff and deltoid muscle; normally a virtual space with no significant measurable fluid.
Biceps Tendon (LHBT)	Centrally located within the bicipital groove without fluid distention in its synovial sheath.
Bony Cortex	Continuous, smooth hyperechoic line with bright specular reflection and posterior acoustic shadowing.

5. Pathological Findings

Ultrasound is highly sensitive and specific for detecting a wide array of shoulder pathologies:

• Rotator Cuff Tendinosis / Tendinopathy: Tendon thickening, heterogeneity, and hypoechoic (dark) appearance with loss of normal fibrillar architecture.
• Rotator Cuff Tears:
  • Full-Thickness Tear: Complete anechoic (black) or mixed-echoic focal defect extending from the bursal surface to the articular surface, often accompanied by tendon retraction and cortical irregularity of the greater tuberosity.
  • Partial-Thickness Tear: Focal anechoic defect involving strictly the bursal surface, articular surface, or intrasubstance of the tendon.
• Calcific Tendinosis: Focal, hyperechoic calcific deposits within the tendon matrix presenting with strong posterior acoustic shadowing.
• Subacromial-Subdeltoid Bursitis: Thickening of bursal synovial walls and/or anechoic fluid distention within the bursa (typically exceeding 2 mm).
• Biceps Tendinopathy & Tenosynovitis: Tendon enlargement, hypoechoic disruption, and fluid circumscribing the tendon sheath.
• Biceps Tendon Dislocation / Subluxation: Medial displacement of the LHBT out of the bicipital groove, frequently associated with subscapularis tears.
• Subacromial Impingement: Real-time dynamic ultrasound reveals pooling/bunching of the SASD bursa or supraspinatus tendon against the acromion margin during abduction.

6. Summary

Shoulder ultrasound is an invaluable, accessible, and dynamic imaging modality for evaluating shoulder pain. Its main strengths lie in its high spatial resolution and real-time assessment of the rotator cuff, biceps tendon, and bursae. When performed by a trained operator using a systematic scanning protocol, ultrasound provides diagnostic accuracy comparable to MRI for rotator cuff and biceps disorders, while also serving as a precise tool for image-guided procedures.

References

1. Jacobson, J. A. (2018). Fundamentals of Musculoskeletal Ultrasound (3rd ed.). Elsevier.
2. Beggs, I. (2011). Ultrasound of the shoulder. Insights into Imaging, 2(2), 99–113.
3. Nazarian, L. N. (2008). The top 10 reasons musculoskeletal sonography is an important complementary or alternative technique to MRI. American Journal of Roentgenology, 190(6), 1621–1626.
4. Roy, J. S., Braën, C., Leblond, J., et al. (2015). Diagnostic accuracy of ultrasonography, MRI and MR arthrography in the characterisation of rotator cuff disorders: a systematic review and meta-analysis. British Journal of Sports Medicine, 49(20), 1316–1328.