Quick Guide to Diagnostic Ultrasound of the Shoulder
Ultrasound is becoming very popular among sports medicine physicians and most fellowships follow the American Academy of Sports Medicine (AMSSM) ultrasound curriculum. There is a wide range of experience in the teachers of the ultrasound curriculums and opportunities to perform diagnostic scans and ultrasound guided injections is variable. It has been shown to be a cost-effective and time-efficient imaging modality with similar diagnostic power as magnetic resonance imaging (MRI.) [1-2]. Most ultrasound machines are portable and applications can be used in the office, operating room, and during sideline athletic event coverage. The most recognized disadvantage to ultrasound as an imaging modality is the fact that it is operator dependent. In the United States, the American Institute of Ultrasound in Medicine (AIUM) and the American Registry for Diagnostic Medical Sonography (ARDMS) provide guidelines and particular MSK ultrasound certifications.
Many sports medicine practices differ in their usage of ultrasound. Some providers perform diagnostic scans for their colleagues and some use ultrasound only for help with needle placement. The amount used also differs among practices with some providers utilizing ultrasound for a majority of their patients, whether it be a limited or complete diagnostic scan or to perform dynamic testing. Regardless of the practice, the shoulder is the most common area that is evaluated with diagnostic scans. It can be very challenging technically due to the anatomy of the humeral head and the presence of anisotropy, or artifact in muscles and tendons. Similar to the MRI, it is important to establish clinical significance of findings, as asymptomatic pathology often occurs in this region with increasing age or activity [4].
The patient should be in a seated position and there needs to be some way to maneuver around the patient. It is ideal to have the examiner’s shoulder above the patient’s shoulder. The time needed to perform a diagnostic scan is usually between 5 minutes and 15 minutes depending on the provider’s experience. It is important to keep in mind what structure is being evaluated and to have the probe in the correct orientation. The transducer frequency for the ultrasound probe should be at least 10 MHz. It is also recommended that a full scan of the shoulder is performed for the shoulder, as pain is often referred or diffuse [3]. Most scans follow a five step approach.
Position one or objective one is to evaluate the long head of the biceps tendon (LHBT). This is the easiest structure to identify due to the bicipital groove. The patient places their hand palm up in supination and rests it on their own leg. The transducer is placed perpendicular to the arm over the proximal shoulder, which is the transverse plane or short axis. Occasional anisotropy can obscure this and this can be corrected by toggling the transducer inferiorly [3]. It is important to evaluate the most proximal aspect where the LHBT courses over the humeral head. Scanning should also be continued inferiorly to the level of the pectoralis tendon, another site for potential pathology. The long axis view is found by keeping the tendon at the center of the probe and screen and rotating 90 degrees on its center axis. Anisotropy can be eliminated by placing pressure on the distal aspect of the transducer, also called the heel-to-toe maneuver. While keeping the bicep tendon in a short axis view, the tendon can be dynamically evaluated for subluxation by internally and externally rotating the arm [4].
Image 1. Position 1 (A), Long axis view proximal biceps in the bicipital groove (B) biceps tendon within the bicipital groove with anisotropy (B) and biceps tendon and overlaying pectoralis major tendon (D)
Image 2. Biceps tendon in long axis.
Position two evaluates the subscapularis tendon and is often performed immediately after the biceps evaluation due to the patient remaining in supination. The transducer is again placed in the transverse plane to again visualize the bicipital groove. The patient is asked to externally rotate the shoulder and this brings the subscapularis tendon into view. The provider should move the transducer both superiorly and inferiorly. This long axis view is the MRI equivalent to the axial view of the subscapularis [4]. Next, center the transducer over the distal subscapularis tendon and rotate 90 degrees for the short axis view. This view shows hyperechoic tendon bundles including the biceps tendon medially. Dynamic testing for subcoracoid impingement can be done by internally and externally rotating the arm to evaluate for impingement of the subscapularis tendon as it slides underneath the coracoid process.
Image 3. Second position evaluating the subscapularis tendon.
More variations exist for positioning due to supraspinatus pathology being most common, but the goal remains to evaluate the tendon in long and short axis. Most evaluate the supraspinatus in the modified Crass or Middleton position, which most patients understand if you ask them to place their hand on their hip or towards their back pocket. This position brings the insertion anterior out of the scapular plane. This is more ideal than the original Crass position, in which the arm is in internal rotation and across the back, due to pain tolerance and better visualization of the rotator interval.
Image 4. Position 3 evaluating the supraspinatus tendon in the modified crass position
Image 5. Example of anisotropy within the supraspinatus tendon.
After assessment in long axis, the short axis can be evaluated by turning the probe 90 degrees. This is the MRI equivalent to the sagittal view [4]. The scan starts at the proximal aspect of the supraspinatus and the operator should toggle and adjust for any anisotropy. The cuff should be similar in thickness and this is known as the “tire on wheel” appearance. The probe is then moved distally as the rotator cuff thins as the supraspinatus is evaluated to its insertion on the superior facet and superior half of the middle facet of the greater tuberosity. The distal portion of the infraspinatus can also be assessed on the inferior portion of the middle facet. It is again important to identify the intra-articular portion of the biceps tendon to ensure the most anterior aspect is evaluated. The rotator cable can be evaluated in most individuals and has a U shape, with each limb attaching to the greater tuberosity.
Image 6. Modified Crass position (A), Normal supraspinatus with uniform thickness and is hyperechoic with intra-articular portion of biceps (B on image B) (B), Sequential images in short axis with the superior and middle facets labeled in image C (SF, MF) that show gradual thinning of supraspinatus (C-E), Long axis image used as reference (F)
Image 7. Rotator cable in long axis (A), and short axis (B)
Position four typically evaluates the acromioclavicular (AC) joint, subacromial-subdeltoid bursa and includes a dynamic evaluation of subacromial impingement. The AC joint can be evaluated by placing the transducer over in the coronal-oblique plane over the distal clavicle and has an appearance of a V shape. The transducer can be moved laterally to assess fluid within the subacromial-subdeltoid bursa. Dynamic testing includes placing the probe in a coronal plane between the acromion and greater tuberosity. When the patient abducts the arm while in internal rotation, the supraspinatus tendon will slide underneath the coracoacromial arch showing potential external impingement. This is shown by pooling of fluid in the subacromial-subdeltoid bursa. The finding of incomplete sliding of the supraspinatus beneath the acromion indicates adhesive capsulitis [3]. A provider can assess for narrowing of the joint by asking the patient to touch their opposite shoulder.
Image 8. Position 4 for evaluating the AC joint
Image 9. AC joint showing hyopechoic joint capsule (B), and imaging more lateral showing anechoic fluid in the subacromial-subdeltoid bursa
Image 10. Positioning to evaluate dynamic testing for subacromial impingement
Image 11. The supraspinatus (SS) glides beneath the acromion. The subacromial-subdeltoid bursa (arrow) remains collapsed without pooling of fluid or bunching of bursal tissue at the acromion tip.
The infraspinatus, teres minor and posterior glenoid labrum can be assessed in position 5. The patient can rest their hand palm side up on the thigh. For the long axis view, the transducer is placed in the oblique axial plane angled superiorly toward the humeral head just below the spine of the scapula [3]. This is the MRI equivalent to the axial plane [4]. The infraspinatus should be easily seen and traced distally to its insertion onto the middle facet that was mentioned earlier. The transducer can be moved inferiorly to visualize the teres minor. The probe can then be moved medially to evaluate the glenohumeral joint and spinoglenoid notch, a common location for paralabral cysts. A dynamic evaluation can be done in this area with internal and external rotation of the shoulder. For the short axis view, the transducer is rotated 90 degrees. The provider must identify the infraspinatus (superior) and teres minor (inferior) within the infraspinatus fossa. The scapular ridge can be seen superiorly and atrophy of the supraspinatus may also be assessed.
Image 12. Position 5 to evaluate the posterior shoulder. Infraspinatus (I), Glenoid (G), Posterior labrum (white arrow in image A), spinoglenoid notch (S)
Image 13. The infraspinatus tendon (solid arrows)
Image 14. Positioning for position 5 in the short axis
Image 15 (A) Progressive transition (B–D) from hypoechoic muscle to hyperechoic tendon of the infraspinatus (open arrows) and teres minor(arrowheads) (left side of image is superior)
Images should be taken to ensure the above is documented. There are many different usages for imaging the shoulder with ultrasound in practice. Dynamic evaluations can not be done with MRI or CT scans and these evaluations can help confirm diagnosis. If there is concern about full thickness tears, many sports practices can do a limited diagnostic scan with point of care ultrasound to help educate the patient and aid in diagnosis. Depending on the relationship with the orthopedic surgeons, some will still proceed with MRI of the shoulder to more completely evaluate the labrum or other structures of concern that may not be seen or completely evaluated with ultrasound.
REFERENCES
2. Roy J-S, Braën C, Leblond J, et al. Diagnostic accuracy of ultrasonography, MRI and MR arthrography in the characterization of rotator cuff disorders: a meta-analysis [published online ahead of print February 11, 2015]. Br J Sports Med. doi:10.1136/bjsports-2014-094148.
4. Panero AJHirahara AM. A guide to ultrasound of the shoulder, part 2: the diagnostic evaluation. Am J Orthop (Belle Mead NJ) 2016; 45: 233–38
5. McNally, E. (2014). Practical Musculoskeletal Ultrasound (2nd ed.). London: Elsevier Health Sciences UK.
