Shoulder 2
The SASD Bursa, Rotator Interval and Other Rotator Cuff Tendons
Subacromial Subdeltoid Bursitis
Ultrasound Appearances
Bursal Fluid
The normal bursa is a thin, low-reflective line surrounded by several layers of bright fat. It is generally no more than 1 mm in thickness but can occasionally be more. When fluid is present, there is separation of the fat layers and low-reflective fluid is detected. It is important not to press too hard with the ultrasound transducer or small quantities of fluid may be compressed out of the field of view and overlooked. If patients are examined in the seated position, it is important to look in the dependent area of the bursa to detect these small quantities of fluid. The probe should be passed around the margin of the deltoid so that the inferior part of the recess can be seen (Fig. 3.1). Another useful place to find small quantities of bursal fluid is anterior to the biceps tendon (Fig. 3.2). When fluid is detected around biceps, care needs to be taken to determine whether it lies within the biceps tendon sheath or within the SASD bursa. Fluid within the biceps tendon sheath extends more distally and surrounds the biceps tendon (Fig. 3.3). Bursal fluid is limited by the lower limit of the bursal space anteriorly and cannot surround the tendon.
Figure 3.1 Coronal image of supraspinatus. The probe has been moved around the lateral margin of the greater tuberosity where a small quantity of fluid is demonstrated in the most dependent part of the bursa (*).
Figure 3.2 Long-axis view of the biceps tendon. Fluid is evident superficial to the tendon (*), but note there is no fluid deep to it. This configuration and the location of the fluid suggest that it lies in the SASD bursa and not within the tendon sheath.
Figure 3.3 Long-axis view of biceps tendon showing fluid within the tendon sheath and SASD bursa. The bursal fluid is more proximal, superficial and deep to the deltoid. The biceps sheath fluid is distal and surrounds the tendon.
If particularly large amounts of fluid are present in the SASD bursa, especially when this is associated with marked thickening of the bursal lining (Fig. 3.4), a cause other than impingement should be considered. Potential diagnoses include rheumatoid arthritis, crystal deposition disease, infection and haemorrhage. Crystal disease can be particularly painful and is suggested when multiple echogenic foci are identified within the thickened synovium and bursal fluid. This condition may progress to frozen shoulder. Haemorrhage within the bursa may also appear echogenic. This can be due to trauma, haemophilia or synovial angiomatous malformation. Less common causes include other synovial-based conditions, including infection, pigmented villo-nodular synovitis and synovial osteochondromatosis.
Figure 3.4 Coronal image of the shoulder. There is marked thickening of the SASD bursa with increased Doppler activity. This indicates a bursitis; however, this pattern is more typical of an inflammatory bursitis than a mechanical one. When this pattern is encountered, an inflammatory arthropathy should be considered.
Bursal Thickening
The more common ultrasound finding in patients with SASD bursitis is thickening of the synovial lining rather than the presence of large quantities of fluid. It should also be appreciated that the bursa may appear normal in patients with painful bursal disease. In such cases, arthroscopy demonstrates a heavily injected but thin bursal lining. In most individuals, the normal bursa is represented by a thin, echo-poor line beneath brighter lines representing peribursal fat. Bursal thickening can be seen anywhere within the bursa, but the common locations to detect it are over the biceps tendon in long axis, around the anterior interval (Fig. 3.5) and, most commonly, over the supraspinatus tendon in the coronal plane (Fig. 3.6), where the bursa abuts the coracoacromial ligament.
Figure 3.5 Axial image of the anterior shoulder. The probe is located over the rotator interval. Note the separation of the coracohumeral ligament from the deep fibres of the deltoid epimysium. The intervening tissue represents thickened SASD bursa (*).
Figure 3.6 Coronal image of the shoulder. There is thickening of the SASD bursa that abuts the coracoacromial ligament (*). The position of the ligament can be identified by a change in contour of the bursa. As the arm abducts, the thickened bursa pushes against the ligament and may even pass suddenly beneath it with an audible/palpable pop.
The range of normal for bursal thickening is also quite large. In some it can be subtle and difficult to differentiate from normal. In others it is markedly thickened and may appear bunched up against the coracoacromial ligament. Just as some symptomatic patients have a normal or minimally enlarged bursa, some patients with obvious bursal thickening may be symptom-free. Focal bursal thickening or side to side difference of >2 mm may be more significant. As with the dynamic assessment of impingement, the patient’s symptoms underpin the diagnosis of impingement, and the diagnosis is unlikely in patients with full and pain-free shoulder abduction, regardless of the degree of bursal thickening.
Dynamic Assessment of Bursal Impingement
Detecting a minimally enlarged bursa is easier with arm movement. As has been described elsewhere, dynamic shoulder assessment is an important adjunct to the static examination and is used to detect more subtle manifestations of cuff and bursal disease. Changes in the configuration of the bursa should be sought during arm abduction as it impinges against either the lateral margin of the acromion or, more preferably, against the coracoacromial ligament (Fig. 3.7).
Figure 3.7 Coronal ultrasound image showing some thickening of the bursa as it abuts the coracoacromial ligament (*). This degree of bursal thickening only occurs during arm abduction and is relatively mild.
The coracoacromial ligament is found by placing the probe in the axial plane over the anterior aspect of the shoulder so that the medial point overlies the bony coracoid. This bony landmark is easy to find with ultrasound, but if necessary, it can also be palpated. From this position, the lateral end of the probe is rotated upwards without moving the medial point. As the acromion comes into view, a ligamentous structure with an ordered homogeneous fibrillary pattern typical of ligaments is visualized (Fig. 3.8). This is the coracoacromial ligament. The probe can then be rotated 90° keeping the ligament in view until it is seen in cross section. In short axis, the ligament is small, bright and oval shaped. With experience, the transverse image of the coracoacromial ligament can be quickly located without the need to find it in long axis. Just lateral to the ligament, the low-signal bursa is identified. The patient’s arm is then abducted and the bursa observed for thickening or bunching as it passes underneath the ligament. In some cases bursal bunching is quite dramatic and further abduction is blocked as the bursa cannot pass deep to the ligament. In others bursal bunching is more subtle and passage under the ligament is not obstructed. In a few patients, the bursa may initially be obstructed, but then passes underneath the ligament with an audible and palpable click. It is important not to press too heavily with the probe as this may impede the normal movement of the bursa or may prevent the bursa from clicking underneath the ligament.
The Biceps Tendon
Biceps Dislocation
Evaluation of the biceps and anterior interval begins with the probe in the axial plane overlying the bicipital groove: an easy to locate depression on the anterior aspect of the proximal humerus. The tendon should be located within the groove, usually surrounded by a small quantity of fluid. If the tendon is not present, it is either dislocated or ruptured. In such cases, the probe should be moved medially to see whether a displaced tendon can be found (Fig. 3.9
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