6 Ultrasound of the Shoulder

Paul S. Ragusa and Uma Srikumaran

Summary

Shoulder ultrasound is a safe, efficient, and cost-effective method used to dynamically evaluate the rotator cuff tendons, biceps tendon, and other structures of the shoulder joint. It is accurate for detecting large and massive rotator cuff tears and is comparable to magnetic resonance imaging (MRI) in both sensitivity and specificity.

Shoulder – ultrasonography – rotator cuff – efficiency – diagnosis

6 Ultrasound of the Shoulder

I. General principles

Ultrasound basics: ¹
1. Ultrasound uses the principles of sonar developed for ships at sea
2. A transducer is used to produce sound waves
3. When the sound waves encounter a border between two tissues that conduct sound differently some of the sound waves bounce back creating an echo
4. The transducer detects the returning echoes which are analyzed by a computer and transformed into an image
5. The more dense the tissue, the brighter the appearance on the image.
Definitions: ¹
1. Echogenicity:
  1. The type of echo display: Anechoic/hypoechoic/hyperechoic.
2. Anechoic:
  1. Without echoes; black; fluid filled structures; in shoulder pathology, anechoic signals typically represents pathology (e.g., effusion, tissue tear).
3. Hypoechoic:
  1. With low-level echoes; grays; more solid structure.
4. Hyperechoic:
  1. Bright echoes; white; dense or strong reflector.
5. Isoechoic:
  1. Same echogenicity.
6. Attenuation:
  1. Loss of energy as a sound pulse travels through a medium.
7. Long-axis:
  1. Along the length of the structure.
8. Short-axis:
  1. Across the width of the structure.
9. Anisotropy:
  1. An artifactual hypoechoic appearance of a normal hyperechoic structure that occurs because the transducer is not perpendicular to the structure being imaged
  2. You can help combat this by maintaining an angle of close to 90 degrees between the probe and the structure of interest.
10. Frequency:
  1. The range of sound waves produced by a transducer (measured in MHz)
  2. The higher the frequency the better image detail, but lesser the penetration; a high-frequency transducer (12 to 15 MHz) is typically used to evaluate the shoulder
  3. The lower the frequency the lesser image detail, but better the penetration; lower frequency transducer (9 MHz) may be used to achieve greater tissue penetration, which may be necessary when evaluating deeper structures such as when evaluating patients with a large body habitus.
Advantages of ultrasound:
1. Cost-effective
2. Safe
3. Improves efficiency in the management of rotator cuff disease ²
4. Dynamic
5. Accurate for detecting large and massive rotator cuff tears ³ , ⁶
6. Comparable to magnetic resonance imaging (MRI) in both sensitivity and specificity ⁷
7. Can be used in patients with contraindications to MRI (pacemaker, claustrophobia, etc.)
8. Accurate for evaluating the rotator cuff in shoulders that have undergone an operation:
  1. Less susceptibility to suture anchor artifact. ⁸
9. Allows for image guided injections.
Disadvantages:
1. Long learning curve:
  1. 100 ultrasound examinations recommended prior to clinical application. ⁹ , ¹⁰
2. Operator dependent
3. Difficult with obese/well-muscled patients
4. Less sensitive for detecting partial-thickness rotator cuff tears and ruptures of the biceps ⁶
5. Does not evaluate intraarticular structures well (labrum, biceps anchor, etc.).

II. Normal shoulder examination

Long head biceps tendon (LHBT):
1. Patient position:
  1. Performed with shoulder in neutral or slight internal rotation, elbow flexed 90 degrees, and forearm supinated and resting on the patient’s lap.
2. Short-axis image (▶ Fig. 6.1a, b ):
  1. Hold the probe transversely with respect to the longitudinal axis of the LHBT
    
    Fig. 6.1 Long head biceps tendon (LHBT). (a) Patient and probe position for imaging the LHBT in short-axis. (b) Short-axis image of LHBT (arrow). (c) Patient and probe position for imaging the LHBT in long-axis. (d) Long-axis image of LHBT (short arrows).
  2. Image is equivalent to an axial view on MRI
  3. Normal appearance:
    - i. Homogeneous, round, or ovoid hyperechoic structure (2–4 mm thick) located in the bicipital groove with trace amount of fluid within its tendon sheath.
3. Long-axis image (▶ Fig. 6.1c, d ):
  1. Rotate the probe 90 degrees so that it is oriented along the longitudinal axis of the LHBT
  2. Image is equivalent to a sagittal-oblique view on MRI
  3. This image is typically used when performing a biceps tendon sheath injection
  4. Normal appearance:
    - i. Smooth and fibrillar.
Subscapularis tendon:
1. Patient position:
  1. Performed with shoulder in external rotation, elbow flexed 90 degrees, and forearm supinated
  2. External rotation delivers the tendon out from underneath the coracoid process.
2. Long-axis image (▶ Fig. 6.2a, b ):
  1. Hold the probe so that it is aligned along the longitudinal axis of the subscapularis muscle fibers
  2. Image is equivalent to an axial view on MRI
  3. Normal appearance:
    - i. Tendon is hyperechoic and convex shaped, tapering toward its insertion on the lesser tuberosity. Normal hypoechoic muscle should not be mistaken for fluid.
3. Short-axis image (▶ Fig. 6.2c, d ):
  1. Rotate the probe 90 degrees so that it is oriented perpendicular to the subscapularis muscle fibers
  2. Image is equivalent to a sagittal-oblique view on MRI
  3. Good for evaluating superior subscapularis tendon tears.
Supraspinatus tendon:
1. Patient position:
  1. Patient is directed to place the palm of his or her hand on the ipsilateral hip or buttock, with elbow flexed and adducted against the body
  2. This allows the supraspinatus tendon to come out from underneath the acromion process.
2. Long-axis image (▶ Fig. 6.3a, b ):
  1. Hold the probe so that it is aligned along the longitudinal axis of the supraspinatus muscle fibers. The muscle fibers and tendon of the supraspinatus are oriented anterolaterally
    
    Fig. 6.2 Subscapularis tendon. (a) Patient and probe position for imaging the subscapularis in long-axis. (b) Long-axis image of subscapularis tendon (arrows). (c) Patient and probe position for imaging the subscapularis in short-axis. (d) Short-axis image of subscapularis tendon (arrows).
  2. While maintaining probe in the same axis, scan from anterior to posterior
  3. Image is equivalent to a coronal-oblique view on MRI
  4. Biceps tendon marks the anterior leading edge of the supraspinatus. Posterior supraspinatus is marked by the change in shape of the greater tuberosity, from ledge-like to flat. This area of transition is where the fibers of the posterior supraspinatus and anterior infraspinatus interdigitate and may be mistaken for a tear if the orientation of the probe is not corrected.
    
    Fig. 6.3 Supraspinatus tendon. (a) Patient and probe position for imaging the supraspinatus in long-axis. (b) Long-axis image of the supraspinatus tendon (arrows). (c) Patient and probe position for imaging the supraspinatus in short-axis. Note long head biceps tendon (LHBT) visualized anterior to the supraspinatus tendon (arrow). (d) Short-axis image of the supraspinatus tendon (short arrows). (e) Illustration of supraspinatus in long-axis (left) and short axis (right) showing the articular (arrows) and bursal (curved arrows) surfaces of the supraspinatus tendon. BT, biceps tendon; ST, supraspinatus tendon. (Adapted from Jacobson JA. Fundamentals of Musculoskeletal Ultrasound.)
  5. Normal appearance:
    - i. Smooth, hyperechoic, and fibrillar, tapering at its insertion or footprint.
  6. Subacromial-subdeltoid bursa:
    - i. The subacromial-subdeltoid bursa is located between the rotator cuff and the overlying deltoid muscle and acromion
    - ii. The bursae is a potential space which consists of a thin hypoechoic band measuring less than 2 mm surrounded by a thin hyperechoic line superficial and deep to this. It should have a smooth appearance throughout.
3. Short-axis image (▶ Fig. 6.4c d ):
  1. Turn probe 90 degrees so that it is aligned perpendicular to the longitudinal axis of the supraspinatus muscle fibers
  2. Image is equivalent to a sagittal-oblique view on MRI
  3. While maintaining probe in the same axis, scan from medial to lateral
  4. Normal appearance:
    - i. The hyperechoic lines of the humeral head and the bursal border of the supraspinatus parallel each other.
Infraspinatus tendon:
1. Patient position:
  1. Performed with shoulder in neutral rotation, elbow flexed 90 degrees, and forearm supinated and resting on the patient’s lap.
2. Long-axis image (▶ Fig. 6.4a, b ):
  1. Hold the probe below the scapular spine. Align it so that it is along the longitudinal axis of the infraspinatus muscle fibers
  2. Image is equivalent to an axial view on MRI
  3. Normal appearance:
    - i. Similar fibrillar pattern as supraspinatus tendon; tendon is hyperechoic and tapers toward its insertion on the greater tuberosity. Central tendon can be identified within the surrounding hypoechoic infraspinatus muscle.
3. Short-axis image (▶ Fig. 6.4c, d ):
  1. Turn probe 90 degrees so that it is aligned perpendicular to the longitudinal axis of the infraspinatus muscle fibers
  2. Image appears similar to sagittal-oblique MRI
  3. While maintaining probe in the same axis, scan from medial to lateral
  4. Normal appearance:
    - i. Similar echogenicity as supraspinatus.
      
      Fig. 6.4 Infraspinatus tendon. (a) Patient and probe position for imaging the infraspinatus in long-axis. (b) Long-axis image of infraspinatus tendon (arrows). (c) Patient and probe position for imaging the infraspinatus in short-axis. (d) Short-axis image of infraspinatus tendon (arrows).
Coracoid and anterior glenohumeral joint:
1. Patient position:
  1. Performed with shoulder in external rotation, elbow flexed 90 degrees, and forearm supinated.
2. Long-axis image (▶ Fig. 6.5a, b ):
  1. Hold the probe in the same position as the long-axis image for the subscapularis tendon (i.e., along the longitudinal axis of the subscapularis muscle fibers). While maintaining the probe in this axis, slide the probe medially
  2. Image is equivalent to an axial view on MRI
    
    Fig. 6.5 Coracoid and anterior glenohumeral joint. (a) Patient and probe position for long-axis view of coracoid and anterior glenohumeral joint. (b) Long-axis image of coracoid (arrow), subscapularis (short arrows) and humeral head (asterisk).
  3. Typically used for measuring the coracohumeral interval and performing anterior glenohumeral joint injections
  4. Normal appearance:
    - i. There should be an absence of fluid inside the joint.
Posterior glenohumeral joint:
1. Patient position:
  1. Performed with shoulder in neutral rotation, elbow flexed 90 degrees, and forearm supinated and resting on the patient’s lap.
2. Long-axis image (▶ Fig. 6.6a–c ):
  1. Hold the probe in the same position as the long-axis image for the infraspinatus (i.e., along the longitudinal axis of the infraspinatus muscle fibers). While maintaining the probe in this axis, slide medially
  2. Image is equivalent to an axial view on MRI
  3. Typically used for posterior glenohumeral joint injections for conditions such as adhesive capsulitis or degenerative joint disease
  4. Normal appearance:
    - i. There should be an absence of any fluid inside the joint.
Acromioclavicular (AC) joint:
1. Patient position:
  1. Performed with shoulder in neutral rotation, elbow flexed 90 degrees, and forearm resting on the patient’s lap.
    
    Fig. 6.6 Posterior glenohumeral joint. (a) Patient and probe position for long-axis view of the posterior glenohumeral joint. (b) Long-axis image of the posterior glenohumeral joint showing the humeral head (long arrow) and glenoid (asterisk) and labrum (short arrow). (c) Illustration of posterior glenohumeral joint.
2. Long-axis image (▶ Fig. 6.7a, b ):
  1. Hold the probe so that it is aligned along the longitudinal axis of the distal end of the clavicle
  2. Image is equivalent to a coronal view
  3. Used for AC joint injections
  4. Normal appearance:
    - i. There should be no abnormal joint widening or narrowing, joint margin irregularity, step-off, or capsular bulging.
      
      Fig. 6.7 Acromioclavicular(AC) joint. (a) Patient and probe position for long-axis view of the AC joint. (b) Long-axis image of the AC joint (asterisk), distal clavicle (long arrow), acromion (short arrow).