Dynamic ultrasound imaging of the posterior capsule in the shoulder: Tips and tricks

1.

Shoulder disorders are commonplace in clinical practice of musculoskeletal physicians. Currently, ultrasound (US) imaging is an established tool to promptly optimize their diagnoses1 and guided interventions.2 Herein, different from the “common” pain generators of the shoulder which are usually evaluated during a routine US examination (eg, subacromial‐subdeltoid bursa, long head of the biceps tendon, rotator cuff),1 the glenohumeral capsule is usually overlooked due to the technical difficulty in distinguishing it from the overlying rotator cuff (ie, low visibility of the acoustic capsule‐tendon interface). On the other hand, it is well known that a posterior capsule hypertrophy/thickening is strongly associated with altered motions of the scapula (ie, scapula dyskinesis),3 loss of internal rotation of the glenohumeral joint and persistent posterior shoulder pain.4

In the pertinent literature, several authors have proposed an US‐guided technique to measure the thickness of the posterior glenohumeral capsule with the shoulder in neutral position. In particular, the tissue immediately lateral to the tip of the posterior labrum, located between the cartilage of the humeral head and the tendons of the rotator cuff is considered.3 However, as the posterior capsule is strictly adherent to the overlying tendons and the deep fascia of the infraspinatus muscle; it is not easy to recognize/measure it. In this sense, we describe a novel technique (with dynamic US imaging) to “separate” the different tissue planes and magnify the acoustic interfaces among the capsule, tendons, and fasciae.

The probe is placed on the posterior aspect of the shoulder inferior to the spine of the scapula in the transverse oblique plane in order to visualize the infraspinatus muscle and tendon in long axis as well as the underlying glenohumeral joint. Starting with the shoulder in 90° of forward flexion, the patient is asked to slowly and horizontally extends the shoulder with the elbow flexed to 90°—to dynamically reproduce the ABER (abduction and external rotation) maneuver (Figure 1 ). During dynamic assessment, one can easily observe the posterior capsule‐synovial complex gliding through the different tissue planes and finally locating between the deep surface of the infraspinatus muscle‐tendon and the posterior labrum (Figure 1, Video S1 ). In this position, the posterior recess is well distinct from the surrounding tissues and can readily be visualized/measured. From the biomechanical point of view, during the ABER maneuver, the infraspinatus tendon physiologically diverges from the posterior capsule which “rolls up” over the posterior labrum/glenoid. Of note, the anatomical “target” we are focusing on is a combination of fibrous capsule (outer layer) and synovial membrane (inner layer); therefore, one layer or both can naturally be involved in shoulder disorders (eg, capsular hypertrophy, synovial proliferation).5

Figure 1.

Position of the probe (black rectangle) on the posterior aspect of the shoulder in the transverse oblique plane during the dynamic assessment (A). Corresponding ultrasound image of the right shoulder (at the end phase of the ABER maneuver) shows the posterior capsule‐synovial complex (yellow arrowheads) over the glenoid (G) and labrum (white asterisk) clearly discernable from the infraspinatus tendon (white arrowhead; B). Schematic drawing illustrates the gliding mechanism of the posterior recess of the shoulder during the dynamic ABER maneuver; that is, the rotation (void curved arrow) of the humeral head (HH) is associated with rolling (dotted arrow) of the posterior joint capsule in a medial direction (C). Gadolinium‐enhanced magnetic resonance arthrography (in ABER position) shows the same anatomical architecture of the posterior shoulder (D). Inf, infraspinatus muscle

CONFLICT OF INTEREST

All authors declare no conflict of interest.

Supporting information

Video S1 Dynamic ultrasound imaging of the posterior shoulder during ABER maneuver.