Keywords

Introduction

The shoulder is one of the largest and most complex joints in the body. It has the greatest range of motion providing the upper extremity with the capability of movements in all planes. The spectrum of pathologies potentially affecting the shoulder is quite different in the children age group compared to adults. The rotator cuff pathology , which is the most common complaint by far in adults as a result of degenerative disease, does not occur in children where positional overload, infection, trauma, dysplasia, and inflammatory disorders are most often observed.

Ultrasound is a very sensitive and well-tolerated imaging modality to examine the musculoskeletal system. The low-cost, non-invasive nature and lack of exposure to ionizing radiations make this technique well suited for assessing pediatric patients. Ultrasound represents an excellent imaging modality to obtain a comprehensive depiction of the main anatomical structure of the shoulder, including joint recesses, bursae, ligaments, muscles, and tendons [5]. In addition, it allows dynamic scanning during joint motion and muscle contraction and can guide minimally invasive interventional procedures.

A deep knowledge of anatomy and the use of a proper scanning technique are prerequisites to perform an accurate shoulder examination with ultrasound. In this chapter, the ultrasound anatomy and the most common pathologies of the shoulder which are of interest to pediatric rheumatologists will be reviewed. Special emphasis will be placed to distinguish normal anatomy from imaging pitfalls related to skeletal maturation.

Shoulder Anatomy

The shoulder joint complex includes the scapula, the clavicle, and the proximal humerus acting as a single biomechanical unit. These bones articulate with each other to form the glenohumeral, acromioclavicular, and sternoclavicular joints [30].

Glenohumeral Joint

The glenohumeral joint is a “ball-and-socket” synovial joint formed by the articular surfaces of the glenoid cavity and the humeral head [3]. The glenoid cavity is smaller than the humeral head and covers only about one-fourth of its convexity. This discrepancy along with the relative laxity of the joint capsule provides wide mobility but makes the joint inherently unstable. A concentric rim of fibrocartilage, the glenoid labrum, increases the size and depth of the glenoid cavity contributing to the stability of the shoulder joint. The articular surfaces of the humeral head and the glenoid fossa are covered by a continuous layer of hyaline cartilage. In the humerus, the articular cartilage invests the convexity of the humeral head until the level of the anatomic neck, where the joint capsule inserts. The fibrous capsule extends from the outer slope of the glenoid rim to the anatomic neck and is lined by synovial membrane. The glenohumeral joint cavity has three main synovial recess: the biceps tendon sheath anteriorly, the subscapularis recess medially, and the axillary pouch inferiorly (Fig. 6.1). The joint capsule has two openings for the passage of the long head of biceps tendon and for the communication with the subscapularis recess. This recess is connected with the joint through an opening located between the superior and middle glenohumeral ligaments (superior subscapularis recess). The long head of the biceps tendon takes its origin from the upper glenoid rim and the supraglenoid tubercle. Its proximal part is intra-articular in location: it has a curvilinear course and reflects over the anterosuperior aspect of the humeral head, between the anterior border of the supraspinatus and the upper edge of the subscapularis. More distally, it descends the arm crossing a groove between the greater and the lesser tuberosity, the so-called intertubercular sulcus . In the bicipital groove, the biceps is surrounded by a synovial sheath as an extension of the synovial lining of the glenohumeral joint. Detection of intrasheath effusion may therefore reflect an underlying joint disease rather than proper tendon pathology [5].

Fig. 6.1
figure 1

Schematic drawing of the glenohumeral joint cavity . The glenohumeral joint has three main recesses: the biceps tendon sheath (1), the axillary pouch (2), and the subscapular recess (3). GT greater tuberosity, LT lesser tuberosity

Full size image

Shoulder Ligaments

In the shoulder, five ligaments represent the main  sources of passive joint stability (Fig. 6.2). They are the three glenohumeral, the coracohumeral, and the coracoacromial. The superior, middle, and inferior glenohumeral ligaments act to stabilize the anterior aspect of the joint. They arise from the outside slope of the glenoid cavity and attach onto the lesser tuberosity. The coracohumeral ligament supports the superior part of the joint capsule and represents the main stabilizer for the long head of the biceps tendon. It consists two bundles of fibers arising from the coracoid, one (lateral ward) inserting into the greater tuberosity and merging with the joint capsule and the supraspinatus and the other (medial ward) inserting into the lesser tuberosity and the subscapularis. This latter band joins the superior glenohumeral ligament to form the so-called reflection pulley . More distally, the coracohumeral ligament continues as the transverse humeral ligament. This latter ligament bridges over the intertubercular sulcus between the lesser and the greater tuberosity transforming the groove in an osteofibrous tunnel for the long head of the biceps tendon. The coracoacromial ligament joins the acromion and the coracoid, as part of the coracoacromial arch. This structure overlies the shoulder joint, preventing superior displacement of the humeral head [5].

Fig. 6.2
figure 2

Sagittal view of the glenohumeral joint over the profile of the bony glenoid (Gl) demonstrates the relationship between the superior (brown), middle (purple), and inferior (green) glenohumeral ligaments with the joint cavity (light blue), the subscapularis (1), and the conjoint tendon of the coracobrachialis and short head of the biceps (2). The subscapularis recess (asterisk) appears a small extension of the joint cavity located between the coracoid (Co) and the upper margin of the subscapularis on the anterior aspet of the joint. This recess is separated from the larger subcoracoid bursa (arrowhead) that is an extension of the subacromial subdeltoid bursa

Full size image

Acromioclavicular Joint and Sternoclavicular Joint

The acromioclavicular joint is a small synovial joint intervening between the medial end of the acromion and the lateral end of the clavicle. Its range of motion is limited. The articular surface of the acromion and the clavicle are invested with hyaline cartilage and are divided by a wedge-shaped disk of fibrocartilage. The joint capsule is attached to the articular margins and reinforced by superior and inferior ligaments.

The sternoclavicular joint is a shallow saddle-shaped joint located between the manubrium of the sternum, the first rib medially and the medial end of clavicle laterally. It represents the only connection between the axial skeleton and the upper extremity. A disk of fibrocartilage splits this joint into medial and lateral cavities, each lined with its own synovial membrane. Costoclavicular and interclavicular ligaments reinforce the joint.

Muscles and Tendons

The muscles around the shoulder may be classified into two groups: intrinsic (i.e., subscapularis, supraspinatus, infraspinatus, teres minor, teres major, and deltoid), which originate and insert on the skeleton of the upper limb, and extrinsic muscles, which join the upper limb with either the spine (i.e., trapezius, latissimus dorsi, levator scapulae, and rhomboid) or the thoracic wall (i.e., serratus anterior, pectoralis minor, and pectoralis major). The rotator cuff consists four muscles that come together as tendons to form a cuff of tissue around the humeral head (Fig. 6.3); it plays an important role as an active stabilizer of the humeral head in the glenoid fossa during movements of the arm. The cuff includes the subscapularis, which is placed on the anterior aspect of the shoulder; the supraspinatus, which lies on its superior aspect; and the infraspinatus and teres minor which are located posteriorly (Fig. 6.4). The subscapularis muscle arises from the subscapular fossa; most of its fibers are directed upward and laterally, running under the coracoid on the anterior aspect of the glenohumeral joint, and attach onto the lesser tuberosity. This tendon serves as an adductor and internal rotator of the arm. The supraspinatus muscle stems from the supraspinous fossa of the scapula and runs underneath the acromion and above the glenohumeral joint before inserting on the greater tuberosity. It acts as abductor and internal rotator of the arm. On the posterior shoulder, the infraspinatus muscle originates from the infraspinatus fossa and converges into a large tendon that extends laterally to attach onto the greater tuberosity, just posterior and inferior to the supraspinatus tendon. The smaller teres minor arises from the lateral border of the scapula and inserts into the greater tuberosity, just posterior and inferior to the infraspinatus. The infraspinatus and teres minor muscles act as external rotators of the arm [5]. In addition to the rotator cuff muscles, the intrinsic muscles of the shoulder include the teres major and the deltoid which forms a roof over the rotator cuff tendons and the glenohumeral joint . The deltoid arises from the lateral third of the clavicle, the acromion and the spine of the scapula and attaches on the anterolateral surface of the mid humeral shaft.

Fig. 6.3
figure 3

Rotator cuff and biceps tendons . Schematic drawing shows the respective relationships of the long head of the biceps (1), subscapularis (2), supraspinatus (3), and infraspinatus (4) at the level of the humeral head. The supraspinatus and infraspinatus merge in a common flattened tendon. The space located between the anterior border of the supraspinatus and the superior edge of the subscapularis is referred to as the rotator cuff interval. It is roofed by the coracohumeral ligament (5) and houses the long head of the biceps

Full size image
Fig. 6.4
figure 4

Anatomy of the rotator cuff . (a) Anterior view of the shoulder shows the subscapularis (SubS) muscle and tendon inserting into the less tuberosity (asterisk) and the long head of the biceps tendon (arrows) descending the curvature of the humeral head and crossing the intertubercular sulcus (arrowhead). (b) Coronal view of the shoulder oriented in the long axis of the supraspinatus tendon (SupraS) demonstrates the extension of glenohumeral joint (1), the subacromial subdeltoid bursa (2), and the acromioclavicular joint (3). The glenohumeral joint cavity extends along the undersurface of the supraspinatus tendon until reaching the anatomic neck (arrowhead) of the humerus. The subacromion subdeltoid bursa lies more superficially, between the supraspinatus and the cover of the deltoid (Del) and the coracoacromioal arch. (c) Posterior view of the shoulder shows the infraspinatus (InfraS) and teres minor (Tm) muscles and tendons located inferior to the scapular spine, in the infraspinous fossa of the scapula. Their tendons insert as paired structures into the posterior aspect of the greater tuberosity (arrow)

Full size image

Shoulder Bursae

Bursae are synovial lined structures, aiming at reducing friction between tendons and other joint structures during joint movements. Several synovial bursae are found around the shoulder. From the clinical point of view, the most relevant are the subacromial-subdeltoid bursa and the subcoracoid bursa. The subacromial-subdeltoid bursa is a broad synovium-lined structure interposed between the coracoacromial arch and the rotator cuff tendons. It consists of a subacromial and a subdeltoid part. Inferior to the coracoid, the subcoracoid bursa intervenes between the subscapularis and the conjoint tendon of the short head of the biceps and coracobrachialis. This bursa is almost invariably in continuity with the subacromial-subdeltoid bursa and may extend medial to the coracoid. Careful scanning technique is needed to avoid confusion between the subcoracoid bursa and the subscapularis recess.

Peculiarities of the Growing Skeleton

The musculoskeletal is a system that undergoes dramatic changes during growth. At birth, the skeleton is purely chondral and, during the ossification process, cartilage is gradually transformed into bone [18]. A deep knowledge of the evolving patterns of normal skeletal development is mandatory for a correct interpretation of ultrasound images and to avoid misdiagnoses [19]. At full-term birth, the humeral diaphysis, the mid-portion of the clavicle, and the body of the scapula are already ossified, whereas the remaining bones of the shoulder girdle are still chondral. As skeletal maturity progresses, multiple secondary ossification centers arise from the epiphyses and apophyses of the shoulder [37]. The proximal humeral epiphysis exhibits three ossification centers for the humeral head, the greater and the lesser tuberosity. These centers fuse with each other at 3–5 years of age (Table 6.1). The ossification of the humeral head is then completed by the age of thirteen [24]. During skeletal maturation, bone irregularities at the physeal borders are a normal occurrence and should not be mistaken for disease-related bone erosions [7].

Table 6.1 Age of appearance and fusion of the ossification centers in the shoulder girdle
Full size table

The scapula has at least seven secondary ossification centers [23]. The ossification of the glenoid starts with the appearance of the subcoracoid ossification center. This appears as a tongue-like opacity and could be misinterpreted as an avulsion fracture. The inferior two-thirds of the glenoid has several ossification centers that grow and fuse together to form a horseshoe-like complex [17]. Complete fusion occurs by 17–18 years of age. The coracoid starts to ossify at 3 months of age. The first ossification center is located in the center of the coracoid process; the second becomes visible at the base of the coracoid at 8–10 years of age. At birth, the acromion is chondral and shows the footprint of the adult acromion. It consists of up to three ossification centers that ossify and fuse during adolescence. Proximal to distal, these centers include the meta-acromion, mesa-acromion, and pre-acromion, respectively. The failure of fusion of these centers can result in an os acromiale that occurs in approximately 1–8% of patients. The os acromiale is triangular in shape and can articulate with the acromion and the clavicle with a proper articulation. The medial epiphysis of the clavicle starts its ossification at 18 years and fuses with the clavicular metaphysis at 22–25 years of age [25]. Familiarity with the timing, location, and appearance of maturation patterns in the pediatric shoulder is crucial for a correct image interpretation and analysis of findings [14].

Sonoanatomy

Musculoskeletal ultrasound applications are quickly evolving due to improved scanner and transducer technology as well as to an increased awareness of their usefulness among pediatric rheumatologists [21]. Regarding ultrasound technology, a linear array high-frequency (range 10–20 MHz) transducer is required for imaging the shoulder in children. Lower frequencies may occasionally be used to visualize the deep anterior recess of the shoulder in overweight children. Doppler imaging can provide information on regional vessels and tissue microvascular states. When assessing the shoulder with ultrasound, an appropriate patient positioning is crucial to visualize the individual anatomical structures. It has to be comfortable for both patient and examiner in order to reduce the examination time as much as possible. A standardized scanning approach is advisable for obtaining better reproducibility of findings. In our opinion, the technical guidelines issued by the European Society of Musculoskeletal Radiology for adults can perfectly meet the needs for shoulder evaluation in children [2, 4].

Long Head of Biceps Tendon

The standardized examination of the shoulder may start with the evaluation of the long head of biceps tendon, keeping the child seated in front of the examiner. The patient’s arm rests on the ipsilateral thigh with elbow flexed at 90° degree and palm upward (Fig. 6.5). The first landmark to identify is the intertubercular sulcus which appears as a groove between the lesser and the greater tuberosities. The appearance of the tuberosities and the sulcus varies with age depending on the degree of skeletal maturation. Placing the probe in a transverse plane over the bicipital groove, the biceps tendon shows a well-defined oval shape. In order to avoid anisotropy, the probe must be kept as perpendicular as possible to the tendon orientation. On the lateral side of the biceps, Doppler imaging may visualize the ascending branch of the anterior circumflex artery. The transverse humeral ligament appears as a thin hyperechoic band bridging over the sulcus. For a complete assessment of the biceps, scanning should be extended upward, to include the intra-articular segment of the tendon as it curves over the convexity of the humeral head, and downward until its myotendinous junction at the level of the pectoralis major tendon (Fig. 6.6a–c). Distal to the humeral tuberosities, the long head lies in front of the proximal humeral metaphysis. It assumes an oblique course, from up down and from anterior to posterior. In this area, a small sheath effusion (e.g., not enough to encircle the tendon) has to be regarded as a normal finding and should not be indicated in the report. Imaging the tendon in the short axis can be enough to screen the status of the biceps. The longitudinal view of the biceps tendon is obtained by rotating the probe ninety degrees clockwise (Fig. 6.7). The long-axis view can also be obtained as a complement of short-axis images to better document abnormal findings.

Fig. 6.5
figure 5

Patient and probe position to examine the long head of the biceps tendon in its short axis

Full size image
Fig. 6.6
figure 6

Long head of the biceps tendon examined in the short axis at the level of the (a) intertubercular sulcus, (b) the most dependent part of its sheath, and (c) the musculotendinous junction. In A, the long head of the biceps tendon (void arrow) appears as an oval hyperechogenic image located between the chondral prominences of the greater (GT) and lesser (LT) tuberosities and covered by the transverse humeral ligament (white arrowhead). In C, note the relationship of the myotendinous junction of the biceps with the pectoralis major tendon (white arrowheads). Void arrowhead, short head of the biceps. Co, coracoid (Co). CoBr, coracobrachialis

Full size image
Fig. 6.7
figure 7

(a) Patient and probe position to examine the long head of the biceps tendon in its long axis. (b) Long-axis US image of the long head of the biceps brachii tendon (arrows) in a 3-year-old girl. The biceps tendon demonstrates a well-defined fibrillar echotexture made up of multiple parallel linear echoes. 1, humeral head; 2, proximal humeral metaphysis; arrowhead, epiphyseal plate

Full size image

Subscapularis Tendon

The subscapularis is the next tendon to be examined in the cuff after the biceps. The child is invited to rotate the arm externally while keeping the elbow in close contact with the body with supinated hand (Fig. 6.8a). On its long axis, the subscapularis tendon has a convex shape over the curved profile of the humeral head (Fig. 6.8b). The insertion of the subscapularis tendon involves a limited portion of the lesser tuberosity. Shifting the probe medially, the short axis of the coracoid tip is visualized as a round bony structure. When examined on its short axis (Fig. 6.8c), the multipennate structure of the normal subscapularis creates a series of hypoechoic clefts related to muscle fibers interwoven with tendon fascicles that should not be mistaken with tendon tears (Fig. 6.8d).

Fig. 6.8
figure 8

Subscapularis tendon . (a) Patient and probe position to examine the subscapularis tendon in its long axis with corresponding (b) transverse 12-5 MHz US image over the long axis of the subscapularis tendon (arrows). Note the footprint (dashed line) showing the insertional area of the subscapularis into the lesser tuberosity that looks still chondral. CoBr, conjoint tendon of the short head of the biceps and the coracobrachialis. (c) Patient and probe position to examine the subscapularis tendon in its short axis with corresponding (d) sagittal 12-5 MHz US image over the short axis of the subscapularis (arrows) shows the multipennate structure of this tendon. Note the nucleus of ossification (1) of the humeral head, the physis (arrowhead), and the metaphysis (2)

Full size image

Supraspinatus Tendon

In neutral position, the supraspinatus tendon is partially masked by the acoustic shadow of the acromion and can only be visualized in its distal part. In order to withdraw the tendon from its bony cover, the patient is invited to extend the arm posteriorly, placing the palm of the hand on the upper part of the iliac wing with the elbow flexed, directed posteriorly and toward the midline (Fig. 6.9a). The probe should be oriented in the long axis of the tendon to visualize simultaneously the convex humeral head invested with cartilage, the anatomic neck of the humerus, and the greater tuberosity. On its long axis, the supraspinatus tendon appears as a convex beak-shaped structure extending deep to the deltoid and the subacromial subdeltoid bursa and superficial to the glenohumeral joint and the articular cartilage (Fig. 6.9b). Anisotropy usually occurs at the insertion of the deep tendon fibers in the area located lateral to the humeral neck. This artifact is a potential mimicker of an articular-sided partial-thickness tear and can be avoided by gently rocking the probe toward lateral to make the ultrasound beam perpendicular to the tendon fibers. The supraspinatus tendon has also to be examined in its short axis. While the anterior margin of the supraspinatus is clearly delineated, there is no definite separation between the supraspinatus and the infraspinatus due to the interwoven arrangement of these tendons.

Fig. 6.9
figure 9

(a) Patient and probe position to examine the supraspinatus tendon in its long axis. (b) Longitudinal axis of the supraspinatus tendon in a 15-year-old girl. The tendon has a convex beak-like shape. It lies over the hypoechoic cartilage (asterisk) of the humeral head before inserting into the greater tuberosity (GT). Note that the tendon insertion (dashed line) extends from the humeral neck (arrowhead) to the superolateral angle of the greater tuberosity. The articular fibers of the tendon assume a curved diverged course in the preinsertional area, possibly leading to a hypoechoic artifact (empty arrow) related to anisotropy. Between the supraspinatus and the deltoid, the normal subacromial-subdeltoid bursa appears as a thin hypoechoic band (empty headarrows)

Full size image

Infraspinatus and Teres Minor Tendons

The infraspinatus and teres minor tendons can be examined by placing the probe over the posterior aspect of the shoulder (Fig. 6.10). The forearm should lie on the ipsilateral thigh in a supinated position. The spine of the scapula can be used as a landmark to differentiate the supraspinous from the infraspinous fossa. The infraspinatus and teres minor tendons can be recognized as separate structures arising from the respective muscles and inserting into the greater tuberosity.

Fig. 6.10
figure 10

Infraspinatus tendon . (a) Probe placement and patient position to examine the external rotators of the shoulder. (b) Transverse 12-5 MHz US image over the posterior aspect of the glenohumeral joint obtained from a 3-year-old boy. US image demonstrates the infraspinatus muscle (1) and tendon (arrowheads) examined in their long axis. Note the relationship of the infraspinatus with the deltoid (2) and the posterior glenoid labrum (arrows). The posteriori recess of the glenohumeral joint is located between the humeral head and the posteriori aspect of the bony glenoid (Gl), deep to the infraspinatus tenon, and muscle

Full size image

Glenohumeral Joint

The glenohumeral joint capsule extends from the outer profile of the glenoid rim to the anatomic neck of the humerus. Ultrasound has high sensitivity to depict even minimal amounts of fluid within the main synovial recesses (i.e., the dependent axillary pouch, the posterior and subscapularis recesses, and the long head of the biceps tendon sheath) of the glenohumeral joint. The posterior recess is examined on transverse planes placing the probe on the posterior aspect of the glenohumeral joint, over the posterior labrum-capsular complex. In its cross section, the fibrocartilaginous labrum appears as a triangular hyperechoic structure with the base directed medially and the apex pointing laterally, capping the bony rim of the glenoid (Fig. 6.10). When synovial hypertrophy /effusion distend the recess, a hypoanechoic area surrounding the tip of the posterior labrum can be observed. Due to the presence of large amounts of anechoic humeral cartilage in younger children, passively assisted movements with internal and external rotation of the arm may make differentiation of effusion/synovium from cartilage more confident by inducing changes in the recess shape. Interventional procedures of needle aspiration or injection can be safely performed to the posterior recess under ultrasound guidance while the patient is seated or prone [26]. The ultrasound evaluation of the anterior recess of the joint is more complex due to its deep location. Fluid distension of this recess can be appreciated on transverse scans as a hypoechoic halo surrounding the anterior labrum. Similarly, the evaluation of the subscapularis recess is challenging due to its small size and location under the coracoid tip. On transverse or sagittal planes, the distension of the subscapularis recess can be appreciated as a small hypoanechoic area located just inferior to the coracoid and superficial to the subscapularis (Fig. 6.11). The small subscapularis recess should not be mistaken for the larger subcoracoid bursa that extends more caudally and does not communicate with the glenohumeral joint.

Fig. 6.11
figure 11

Transverse power Doppler 13-5 MHz US image over the anteromedial space of the shoulder in a 11-year-old girl with juvenile idiopathic arthritis and shoulder involvement. US image shows the subscapularis recess (arrow) distended by hypervascular synovium. Note the relationship of this recess with the subscapularis tendon (SubS) and the coracoid (Co)

Full size image

The axillary recess of the glenohumeral joint results from a redundant folding of the inferior joint capsule. The examination of this recess can be performed by keeping the patient supine with abducted arm. The probe is placed in a longitudinal plane on the mid-axillary line, oriented in the long axis of the humeral shaft (Fig. 6.12a). This allows the identification of the synovial recess using the humerus head-glenoid complex and the humeral neck as landmarks (Fig. 6.12b). Distension of this recess may extend along the humeral neck. The amount of distension of the axillary recess can be measured in the middle of the humeral surgical neck concavity, where its thickness is maximal. If children cannot abduct the arm due to reduced shoulder mobility, an alternative technique can be carried out in neutral position by sweeping the probe inferior to the posterior recess in a transverse plane. Finally, the biceps tendon sheath can be considered a mere extension of the joint cavity. Sheath effusion secondary to an isolated biceps tendinitis is rare.

Fig. 6.12
figure 12

(a) Patient and probe position to examine the axillary recess of the glenohumeral joint . The transducer is placed in a longitudinal plane on the mid-axillary line and along the long axis of the humeral shaft. (b) Axillary recess of the glenohumeral joint . 1: humeral head; 2: humeral metaphysis; white arrowhead: epiphyseal plate. Distension of the axillary recess can be measured in the middle of the humeral surgical neck concavity, where its thickness is maximal (double-headed arrow)

Full size image

Subacromial Subdeltoid Bursa

The subacromial subdeltoid bursa is the most extended synovial-lined bursa in the body. Ultrasound can visualize this bursa where it is exposed to the ultrasound beam. The bursal portion located deep to the acromion is not accessible. In normal conditions, the subacromial-subdeltoid bursa is collapsed and appears as a thin hypoechoic band overlying the supraspinatus tendon . In chronic inflammatory conditions, the synovial membrane of the bursa walls may thicken and the cavity may be distended. A careful scanning technique is needed when examining the bursa: an excessive pressure with the probe may squeeze the fluid away from the field of view. With the patient seated, the effusion tends to collect in the most dependent parts of the bursa, along the lateral edge of the greater tuberosity, producing a typical “teardrop” shape.

Acromioclavicular Joint

To examine the acromioclavicular joint, the transducer is placed over the top of the shoulder in a coronal plane (Fig. 6.13). The end of the clavicle rides higher than the acromion and is easily palpable. Once the joint is detected, the probe orientation should be adjusted placing one of its edges over the acromion and the other over the clavicle. Joint distension by hypertrophic synovium/effusion can be appreciated as widening of the joint space or bulging of the superior acromioclavicular ligament and the joint capsule. The internal fibrocartilaginous disk can be seen as a hyperechoic triangle located intra-articularly.

Fig. 6.13
figure 13

Patient and probe position (a) to examine the acromion clavicular joint with corresponding (b) US image obtained from a 11-year-old girl

Full size image

Shoulder Pathology

Juvenile Idiopathic Arthritis

By systematic evaluation of the joint recesses, ultrasound has proved to be a valuable tool for assessment of shoulder involvement in juvenile idiopathic arthritis (JIA) . JIA does not represent a single disease form but a diagnosis that applies to all forms of arthritis of unknown origin lasting >6 weeks with onset prior to the 16th year of age [29]. Joint involvement may be either monoarticular or oligoarticular or polyarticular depending on the specific JIA category [28]. All JIA categories have in common a chronic inflammatory process primarily targeting the synovial membrane. In more severe cases, persistence of inflammation may lead to an increased risk of osteochondral damage that is potentially responsible for both short-term and long-term physical disability. Although any joint can potentially be involved, in the oligoarticular forms of JIA large joints such as the knee and the ankle are commonly affected with limping as the leading symptom at onset. In the shoulder, arthritis occurs in polyarticular and systemic-onset categories more often than in oligoarticular JIA. In this setting, ultrasound may be regarded as a valuable extension of physical examination able to provide information on the anatomic structures that are most commonly affected by the inflammatory process [8] (Table 6.2).

Table 6.2 Anatomical structures most commonly detectable by shoulder ultrasound in juvenile idiopathic arthritis
Full size table

It has proved to be very sensitive in detecting inflammatory changes, such as effusion and synovial hypertrophy (Fig. 6.14). In younger children, the epiphyseal cartilage looks anechoic as the synovial fluid, thus creating some difficulties in judging the presence of effusion for the inexperienced examiner. An in-depth knowledge of appropriate anatomic landmarks and analysis of subsynovial fat may make this differentiation easier. Becoming familiar with the joint appearance at different ages is part of the learning curve and a major research focus of the Outcome Measures in Rheumatology and Clinical Trials (OMERACT) ultrasound special interest group in JIA, which successfully provided ultrasound definitions for the normal pediatric joint [32]. Detailed knowledge of age-related changes of the growing skeleton provides the basis to develop definitions for pathology and support the standardized use of ultrasound in pediatric rheumatology [9, 33]. Although intrinsically inaccurate, the quantitative assessment of synovitis may be attempted by measuring the maximal thickness (i.e., distance between the humeral head and the joint capsule) of the posterior and axillary recesses (Fig. 6.15) [35]. Synovial hyperemia , which is expression of synovial inflammation, can be demonstrated by an increased number and intensity of Doppler blood flow signals. Different from the articular cartilage that is nourished by synovial fluid, the epiphyseal cartilage exhibits a proper vasculature. The cartilage vascularization patterns however show some age- and joint-related variability [36]. The knowledge of the vascular architecture in the immature skeleton is essential for a correct interpretation of the paraarticular Doppler signals in JIA patients as detection of blood flow in the growing epiphyseal cartilage is not a disease-specific finding reflecting the only inflammatory process.

Fig. 6.14
figure 14

Juvenile idiopathic arthritis . (a) Transverse 12-5 MHz US image over the posterior aspect of the shoulder in a 11-year-old child shows the posterior labrum (arrow) inserting into the bony glenoid (Gl) and mild effusion (asterisk) distending the posterior recess of the glenohumeral joint. (b) Corresponding power Doppler image reveals signs of hyperemia at the level of the synovial walls of the recess

Full size image
Fig. 6.15
figure 15

Distension of the axillary recess (double-headed arrow) of the glenohumeral joint in an 11-year-old girl with juvenile idiopathic arthritis and shoulder involvement

Full size image

As anticipated, in the bicipital groove, the biceps is surrounded by a synovial sheath as an extension of the synovial lining of the glenohumeral joint; in JIA patients with gleno-humeral joint involvement is quite common to detect intrasheath effusion, hyperemia and sheath thickening of the biceps tendon (Fig. 6.16). Hypertrophied synovitis in the subacromial-subdeltoid bursa [34] has been occasionally reported in patients with JIA. Ultrasound is also helpful to evaluate signs of osteochondral damage, such as thinning of the articular cartilage and bone erosions in case of longstanding disease. As the skeletal maturation progresses, the width of joint spaces physiologically decreases, making it difficult to determine whether a decrease in cartilage thickness is part of age-related changes or erosive disease. In chronic advanced disease, ultrasound can visualize bone erosions which appear as well-defined cortical defects filled by hypoechoic synovial pannus (Fig. 6.17a, b) [1].

Fig. 6.16
figure 16

(a) Long head of the biceps tendon examined in the short axis (arrowhead) in a 12-year-old girl with juvenile idiopathic arthritis. The sheath of the biceps tendon is distended by fluid (asterisk). Corresponding (b) US Power Doppler image shows synovial hyperemia

Full size image
Fig. 6.17
figure 17

(a) Ultrasound image obtained from a 16-year-old-girl with juvenile idiopathic arthritis showing bone erosions (arrows) in the humeral head (H). (b) 3D gradient echo T1-weighted MRI sequence confirms the presence of bone erosions in the humeral head

Full size image

Septic Arthritis

Glenohumeral joint infection is a severe but relatively uncommon condition in the children age group, accounting for approximately 3–12% of all cases of septic arthritis [20]. It predominantly occurs in very young infants. Since septic arthritis is considered a medical emergency, prompt diagnosis and aggressive treatment are required to avoid permanent joint damage. Fluid distension of the joint cavity, synovial hyperemia, and associated paraarticular soft-tissue changes, including edema, fluid collections, and local hyperemia, are common findings on ultrasound images. Although ultrasound is very sensitive for detection of glenohumeral joint fluid, it does not allow to safely characterize the nature of the effusion and differentiate septic arthritis from other conditions. In many instances, purulent effusions may appear turbid and echogenic, but the infectious nature of an intra-articular effusion cannot be excluded based on echotextural criteria. Limpid and anechoic effusions may in fact be septic in nature. Given these considerations, needle aspiration of the effusion, possibly guided by ultrasound, remains the mandatory key for the diagnosis in suspected infectious disease.

Sports-Related Injuries

The ability of ultrasound to provide depiction of chondral structures and growth plates in young children has opened a new and rewarding option for imaging of traumatic alterations of growing joints. Although there is obvious overlap between sports-related injuries in the pediatric age group and adult population, relevant features can be distinguished in the injury patterns of pediatric patients. These differences are mainly related to the ongoing changes in the immature skeleton and paraarticular structures. It is estimated that ligamentous structures are two to five times stronger than open physes [6]. The disparity in stress resistance between growing bones and adjacent tendons and ligaments predisposes to acute and chronic injuries in children. The shoulder is one of the most common sites of injury in pediatric throwing athletes [27]. The little league shoulder and acromial apophyseosteolysis are examples of common injury patterns restricted to adolescent throwing athletes. The little league shoulder is caused by microtrauma due to repetitive overhead throwing, resulting in disruption of the vascular network located in the medullary bone at the proximal humeral metaphysis [11, 22, 31]. The subsequent defective blood supply impairs the process of ossification of the physis and leads to physeal thickening and irregularity on radiographs and MR images. An early diagnosis is of critical importance for minimizing long-term adverse sequelae such as formation of bone bridges. Specific acute injury patterns affecting pediatric athletes who practice contact sports include physeal fractures of the proximal and distal end of the clavicle (periosteal sleeve fracture) of the proximal humeral physis and the coracoid process.

Clavicle Fracture

Clavicular fractures are a common pediatric injury with an incidence of 5–12/104 cases per year [10]. Radiography is the imaging modality of choice to confirm the diagnosis, although ultrasound may be considered a valuable alternative with 95% accuracy [12, 13]. The ability of ultrasound to visualize bones that are partially chondral makes this technique suitable to diagnose clavicle fractures in neonates due to birth trauma [15, 16]. The diagnosis is based on detection of cortical bone discontinuity. Depiction of a callus, hematoma, or paradoxical motion of bone fragments during breath are other relevant diagnostic signs [13].