The use of ultrasound in the assessment of the glenoid labrum of the glenohumeral joint. Part II: Examples of labral pathologies.

Labral pathologies of the glenohumeral joint are most commonly caused by trauma. The majority of lesions affect the anterior part of labrum, resulting from much higher frequency of anterior shoulder dislocations over posterior ones. Another subgroup of labral lesions, not directly related to joint instability, are SLAP tears. Other findings include degenerative changes of labrum and paralabral cysts. Diagnostic imaging is crucial for making a decision regarding operative treatment. Apart from a standard X-ray examination, the imaging mainly relies on magnetic resonance or computed tomography arthrography. Based on their own experience, the authors propose the use of ultrasound in the assessment of labral tears of the glenohumeral joint. Different signs indicating labral pathology may be discovered and assessed during ultrasound examination. They include permanent displacement of the labrum onto the glenoid, labral instability during dynamic examination, lack of the labrum in the anatomical position, hypoechoic zone at the base of the labrum >2 mm in width, residual or swollen labrum as well as paralabral cyst(s). The most frequent appearance of labral pathology is displacement of the anteroinferior labrum onto the external aspect of the glenoid typically seen after anterior shoulder dislocation. The another most important US feature is labral instability while dynamically examined. The swelling or reduced size of the labrum usually indicates degeneration. This article presents sonographic images of selected labral pathologies.

Introduction

Injuries to the glenoid labrum of the glenohumeral joint usually have a traumatic origin, and more rarely a degenerative etiology. The overwhelming majority of lesions involve the anterior part of the labrum, as within the group of shoulder instabilities, the anterior instability dominates. Most commonly, the joint instability is a result of previous trauma. The trauma causes irreversible damage to the labral-ligamentous complex, which can predispose to further joint dislocations (not uncommonly recurrent or even habitual ones). Other causes of instability may be associated with generalized flaccidity of the joints, neuromuscular disorders and muscle dysfunction, as well as acquired or congenital bone defects, for example glenoid cavity hypoplasia(. Untreated instability is dangerous for the joint, as it leads to damage of cartilage and progression of degenerative changes. Moreover, the resulting functional limitations of the upper limb cause the patient significant discomfort. This issue is all the more relevant, as it affects mostly young and active persons. A second group of labral pathologies, not directly associated with shoulder instability, are injuries to the superior labrum, known as SLAP (superior labrum anterior-posterior) lesions, which occur in 3.9–6% of cases(. Among other pathologies, degenerative changes of the glenoid labrum and paralabral cysts are also found.

Notes on the diagnostic imaging of the glenoid labrum

The initial imaging modality for diagnosing shoulder pathologies should be radiography (X-ray). On the basis of X-rays, it is possible to assess the bony anatomy of the shoulder and to confirm or rule out the presence of traumatic or degenerative changes within the bones. Whereas for the evaluation of the soft tissues of the shoulder, magnetic resonance imaging (MRI) is recommended, and is considered the imaging method of choice. In patients with clinically diagnosed shoulder instability or suspicion of a SLAP tear, MRI with intra-articular administration of contrast medium (MR arthrography) is used for better assessment of the glenoid labrum and the capsular-ligamentous complex(. The benefits of MRI include excellent tissue contrast along with high spatial resolution, and lack of exposure to radiation. High study cost and still limited availability are the downsides of MRI. If there are contraindications to MRI or the study is unavailable, it may be substituted by computed tomography with intra-articular contrast dye injection (CT arthrography), which has a comparable to MR artrhrography diagnostic value in detection of labral injuries(. CT also allows for precise imaging of the bony structures with the possibility of assessing the glenoid cavity morphology on the basis of multiplanar and 3-dimensional (3D) reconstructions. The CT study is especially indicated in the pre-operative diagnostics of Bankart lesions with fractures of the glenoid(. The main downside of CT is the exposure of the patient to radiation. Compared to MRI, CT has a worse ability to precisely image the soft tissues of the joint, including the rotator cuff.

What could be the role of ultrasound (US) in the diagnosis of labral pathologies of the shoulder? Since many years, the US examination has had an established role in the diagnostics of musculoskeletal pathologies. Important benefits of US include its wide availability, lack of contraindications, and the possibility of a dynamic assessment. A relevant disadvantage of US is the large dependence on the experience of the examiner resulting in a subjective assessment, as well as the quality of the ultrasound equipment. Among shoulder pathologies, US has been widely used in evaluating the rotator cuff and other muscles, shoulder impingement syndromes, particularly subacromial impingement, subacromial-subdeltoid bursitis, inflammatory changes, compression neuropathies and acromioclavicular and sternoclavicular joints injuries(. Some papers also indicates the utility of US in assessing the glenoid labrum(. Despite these latter reports, US is usually completely omitted from the diagnostic algorithms for shoulder instability. Several years of the authors’ clinical experience indicate that US can image most parts of the glenoid labrum (see part I of the article). This imaging technique also allows for the visualization of other changes associated with a shoulder dislocation, such as the impaction injuries of the humerus (Hill-Sachs lesion, McLaughlin lesion) or loose intraarticular bodies(.

Examples of labral pathologies in the US examination

When evaluating the glenoid labrum, it is always recommended to compare findings with the healthy side. The following US features confirm a pathology of the labrum(:

permanent displacement of the labrum onto the external part of the glenoid;

labral instability in the dynamic examination;

lack of the labrum in the anatomical position;

hypoechoic zone at the base of the labrum, >2 mm in width;

residual or swollen labrum;

paralabral cyst(s).

Lesions of the posterior part of the glenoid labrum are rather uncommon. They can result from trauma (posterior dislocation of the shoulder), degenerative changes as well as internal impingement syndromes (the posterosuperior or posterior ones). The posterior shoulder dislocations mainly cause injury to the posteroinferior part of the labrum. The possible post-traumatic findings include injuries similar in appearance to those of the Bankart-type (“reversed Bankart”, POLPSA type) with or without fracture of the glenoid rim. Injuries to the posterior labrum may coexist with lesion of the anterior labrum, in cases of multidirectional instability of the shoulder. In internal impingement syndromes, the labrum is most commonly affected in its posterosuperior or superior parts (SLAP tears)(. A sure sign of labral pathology in the US examination is a labral avulsion and displacement onto the external aspect of the glenoid, or a lack of the labrum in its anatomical position (fig. 1). The depiction of pathologies is facilitated by the increased amount of joint fluid. In posterior instability, the head of the humerus moves more posteriorly, “sticking out” of the glenoid cavity to a larger extent than on the healthy side. The assessment should also be performed in a patient-provoked subluxation of the shoulder if it is possible.

Fig. 1

Lesions of the posterior glenoid labrum: A. an irregular, decreased in size labrum (arrows); B. a labrum avulsed and displaced onto the glenoid (arrows); H – head of the humerus, moved backwards in relation to the glenoid (B), ISP – the infraspinatus muscle; joint fluid (*)

To the group of labral pathologies belong paralabral cysts, which most often occur in the posterior and superior parts of the shoulder joint (fig. 2). The mechanism of paralabral cyst formation is similar to meniscal cysts, and is related to degenerative changes and/or small tears of the labrum, through which the joint fluid passes outside the joint to form paralabral collections. Paralabral cysts may also coexist with large labral tears. Large cysts may be localized in the area of the scapular neck and extend towards the supraspinous or infraspinous fossa, causing compression (entrapment) of the suprascapular nerve as it runs through the supraglenoid and the spinoglenoid notch of the scapula (fig. 2 C). It is also possible to puncture the cyst under US guidance, aspirate its content and inject steroids into its lumen(.

Fig. 2

Paralabral cysts in the posterior region of the shoulder: A. a small cyst (arrow) of the labrum (*) with a small fissure representing labral tear (arrowheads); B. a larger cyst (arrows) near the labrum (*); C. a large paralabral cyst (arrows) in the spinoglenoid notch; Gle – the glenoid, H – the head of the humerus

Lesions of the anterior labrum are the most common pathologies of the capsular-ligamentous-labral complex(. They are usually the result of an anterior dislocation of the shoulder, and primarily affect the anteroinferior part of the labrum. This group contains Bankart lesions, with or without fractures of the glenoid rim (“bony Bankart”) or so-called Bankart-variants (ALPSA, Perthes, and GLAD lesions). The labral injuries are often accompanied by post-traumatic changes to the joint capsule and glenohumeral ligaments (especially the inferior one), which may be sometimes the dominant element of the injury to the entire complex (ex. HAGL, avulsion of the scapular attachment of the IGHL)(.

The authors’ experience indicates, that the most common pathology seen on US in patients after anterior shoulder dislocation is a permanent displacement of the anteroinferior part of the labrum (sometimes along with the anterosuperior part) onto the external contour of the glenoid, with an altered architecture of the entire capsular-labral complex (fig. 3). The avulsed labrum along with the injured capsular-labral complex, with time undergoes healing and scarring, and it may sometimes re-attach to the glenoid in a non-anatomical position. In the case of acute injury, with a hematoma present, ultrasound can show fluid penetrating between the injured structures. In the authors’ opinion, a characteristic finding indicating an injury of the capsular-labral complex, are calcifications – small or large, single or multiple – located near the external aspect of the glenoid, readily depicted by US. They may represent avulsed bone fragments (usually not visible on the X-ray or not recognizable on MRI images) or be calcified periosteal scars (fig. 3). This sign is highly specific for a Bankart injury. In the case of small fractures of the glenoid rim, a “V”-shaped deformity on the external contour of the glenoid is seen (fig. 3 B, 4).

Fig. 3

A. Injury to the anterior capsular-labral complex (arrowheads) with thickening of the capsular structures and displacement of the avulsed labrum (*) on the external aspect of the glenoid; a small post-traumatic calcification (arrow). B. An avulsed fragment of the glenoid (arrow) along with the detached labrum (*); Gle – the glenoid, H – the head of the humerus, SSC – the subscapularis muscle

Fig. 4

Bankart lesion with a typical “V”-shaped deformity of the external aspect of the glenoid; Gle – the glenoid, H – the head of the humerus, the damaged labrum (*)

A second sign indicative of labral injury, is instability of the labrum in the dynamic examination. During internal rotation of the upper extremity, the head of the humerus presses upon the labrum with the joint capsule being relaxed, causing a minor turning of the labrum in the anterior direction. Sometimes the joint capsule may be seen a little sliding against the labrum. In the case of post-traumatic changes without a permanent displacement of the labrum (for example in Perthes injuries), the labrum is properly located when the upper limb is in the intermediate rotation. In contrast, when the limb internally rotates the labrum clearly deviates or even displaces in the anteromedial direction, while the opposite rotation returns the labrum into its initial position (fig. 5). In authors’ opinion, it is more difficult to obtain a distinct “dislocation” of the labrum in external rotation of the limb in 90° abduction, even though this is the standard position used for the clinical examination (anterior apprehension test). The dynamic examination of the labrum may be difficult or even impossible to do in cases of acute injuries, due to limited mobility of the joint secondary to pain. In patients with chronic anterior joint instability, a more prominent anterior protrusion of the humeral head with respect to the glenoid may be observed on ultrasound (anterior subluxation). When the probe is applied from the posterior aspect of the joint, the “regression” of the humeral head relative to the glenoid's contour will be seen. The US study may also be used to assess the stability of the glenoid labrum after a surgical repair. The rules for dynamic evaluation are the same as for preoperative patients.

Fig. 5

Injury to the anteroinferior part of the labrum (Perthes type lesion): A. the capsular-labral complex (arrows) with the non-displaced labrum (thick arrow); the upper limb in intermediate rotation; B. in internal rotation, the labrum (along with the overlying joint capsule) (arrows) gradually displaces onto the glenoid under the pressure of the humeral head; C. the labrum completely dislocated onto the external aspect of the glenoid; H – the head of the humerus, Gle – the glenoid

Another pathological finding is the absence of the labrum in its anatomical position. In this case, a contour of a “naked” glenoid is visible, and barely discernible fragments of the labrum may be found on the external surface of the glenoid. The assessment is facilitated by the increased amount of fluid in the joint (fig. 6). Some developmental variants, especially those with glenoid labrum hypoplasia, should be kept in mind. Labral hypoplasia may affect the anterior and posterior parts of the glenohumeral joint, but it is most often found in the anterosuperior region, as part of the so-called Buford complex (occurring in approximately 6% of cases) – above the region of the labrum most affected by traumatic injuries accompanying anterior instability of the shoulder( (fig. 7).

Fig. 6

A lack of a labral echo in the expected position: the “empty” edge of the glenoid (thick arrow); irregular contours of the anterior capsule from the joint side – post-traumatic changes (thin arrows); H – the head of the humerus, Gle – the glenoid

Fig. 7

The Buford complex: A. a hypoplastic anterosuperior labrum with the thick middle glenohumeral ligament resembling the labrum (arrow); a flattened outline of the glenoid; B. on the contralateral side, in the same region, a normal labrum is visible (*) along with the more oblique outline of the glenoid; H – the head of the humerus, Gle – the glenoid

A sign of labral injury described in the literature is the presence of a hypoechoic area at the base of the labrum, >2 mm in width (compared to the normal transitional fibrocartilage of <2 mm in width)(. This finding may be observed in injuries with partial avulsion of the labrum from the glenoid (fig. 8), which are not always well depicted on US. Thus the usefulness of this criterion is disputable, although along with instability of the labrum in the dynamic examination, it definitely indicates an injury.

Fig. 8

A hypoechogenic area (arrows) at the base of the labrum (*) indicating the detachment from the glenoid; the injury also affects the attachment site of the joint capsule (arrowheads); H – the head of the humerus, Gle – the glenoid, SSC – the subscapularis muscle

As for degenerative changes of the labrum, they are manifested by a heterogenous echogenicity as well as a decrease or increase in size (edema) of the glenoid labrum. Irregular boundaries of the labrum are found even in normal conditions, so they should not be considered pathological. Sometimes bubbles of gas may be noticed in the area of a degenerative labrum(. It should be remembered, that not visualizing any labral changes in the US study, both with respect to labral morphology as its stability, does not exclude the presence of pathology when such is suggested in the clinical examination. In these cases MR arthography or CT arthography should be performed.

Injuries to the superior part of the glenoid labrum (SLAP lesions) represent the labral pathology not directly related to shoulder instability(). They often affect people who perform sports which involve overhead activity (overhead throwers) – baseball, basketball, volleyball, javelin throw, disc throw, etc., as well as swimming or weight lifting. They also occur in those doing manual labor with frequent excessive abduction and external rotation, and then have the character of fatigue injury. Sometimes SLAP lesions may be caused by isolated trauma, for example after a fall on an extended extremity or from pulling the limb upwards(. Many types of SLAP injuries have been described, based upon the morphology and extent of changes, whose classification – even based upon MRI – is still challenging(. There is a lack of published reports on the use of US in the assessment of SLAP lesions. According to the authors, ultrasound may also be used in the diagnosis of SLAP injuries to show the instability of the labrum or the superior biceps-labral complex. In the dynamic examination, labral displacement should be sought (fig. 9). Sometimes it is possible to visualize even smaller lesions, without clear signs of instability or with only minor instability of the labrum (fig. 10).

Fig. 9

Lesion of the superior part of the labrum (SLAP tear). The dynamic US study, with the probe applied anterior to the clavicle, shows the phases of the labrum's displacement (arrows) onto the upper part of the glenoid: A. the labrum in the anatomical position; B. flattening of the labrum with partial displacement onto the glenoid; C. complete “inversion” of the labrum onto the upper surface of the glenoid; H – the head of the humerus, Gle – the glenoid, Cla – acoustic shadow of the clavicle, SSP – the tendon of the supraspinatus muscle

Fig. 10

SLAP lesions. The US examination in 3 different patients, with probe applied right posterior to the clavicle. Fissures representing labral tears (arrows): with an oblique course (A) and a vertical one (B); irregular lesion/degeneration of the superior labrum (arrows) (C); H – the head of the humerus, Gle – the glenoid, Ac – the acoustic shadow of the acromion, SSP – the supraspinatus muscle

Conclusion

Based on own studies, the authors are convinced of the utility of ultrasound in the diagnosis of pathologies of the glenoid labrum. An important benefit of US is the possibility of a dynamic assessment and simultaneous comparison of the examined side to the healthy one. Arthroscopic verification confirms the high diagnostic efficacy of US in Bankart lesions. Paralabral cysts are also well imaged on US. The US study may be useful in the diagnostics of SLAP injuries, but this still remains controversial and requires further evaluation.