Sonographic assessment of the anatomy and common pathologies of clinically important bursae

Subacromial-subdeltoid bursa is clinically the most important bursa of the shoulder. However, there are also several other bursae around the shoulder joint: coracobrachial bursa, subcoracoid bursae, and subscapularis subtendinous bursa⁽⁷⁾.

Subacromial-subdeltoid bursa is the largest bursa of the human body, but the two walls of the bursa are normally only up to 2 mm apart⁽⁸⁾. It is composed of subacromial and subdeltoid portions, which in the majority of people communicate by a connective tissue band⁽⁹⁾. Normal subacromial-subdeltoid bursa is localized between the rotator cuff tendons and the deltoid muscle, and the rotator cuff tendons and the acromion.

For the best representation of the bursa by ultrasound, the patient’s hand should be resting on the iliac wing, while the arm should be positioned posteriorly. The transducer should follow the long axis of the supraspinatus tendon (Fig. 3A). The bursa is normally visible on the ultrasound scan as a thin, linear, anechoic structure between hyperechoic peribursal fat, but the synovia is not apparent on ultrasound⁽⁸⁾ (Fig. 3B).

Fig. 3.

One may distinguish between communicating and non-communicating subacromial-subdeltoid bursitis⁽¹⁰⁾. The most common type of subacromial-subdeltoid bursitis is the communicating variant, when the bursa interconnects with the glenohumeral joint. It occurs in cases involving a total rotator cuff tear, either traumatic or degenerative in nature (Fig. 4). Non-communicating subacromial-subdeltoid bursitis could be a result of shoulder overuse, direct traumatic blow to the bursa, osteoarthritis, rheumatoid arthritis, etc. (Fig. 5).

Fig. 4.

Fig. 5.

Two clinically important bursae are localized near the elbow. Bicipitoradial bursa, around the distal biceps tendon, and superficial olecranon bursa. Olecranon bursa is the most superficial bursa of the human body. It is positioned between the ulnar olecranon and the skin. Olecranon bursa is normally not visible on ultrasound.

To achieve the best sonographic evaluation of the bursa, the patient’s hand and elbow should be in 90 degrees flexion, with the palmar side of the hand facing towards the table. The transducer should be positioned in the longitudinal or transverse plane, over the olecranon of the ulna which is used as a bony landmark (Fig. 6A). Olecranon bursitis often occurs in persons with more pronounced, palpable olecranon (Fig. 6B and C). Common etiology includes a traumatic event or infection; even a minor, sometimes neglected trauma or repetitive microtrauma can lead to olecranon bursitis (also known as student’s elbow, miner’s elbow)⁽¹¹⁾. However, septic olecranon bursitis is not uncommon either, due to its superficial localization and poor vascularity, particularly in immunocompromised patients⁽¹²⁾, occurring in about a third of patients with bursal inflammation⁽¹¹⁾. Olecranon bursa is most commonly affected by inflammation of all the constant bursae⁽¹²⁾.

Fig. 6.

There are three bursae around the trochanter major of the femur. Trochanteric bursa, which is the largest of the three, covers the lateral insertion of the medial gluteus muscle and posterior trochanteric facet. Subgluteus medius bursa is located between the tendon of gluteus medius and the lateral facet. Subgluteus minimus bursa can be found between the gluteus minimus tendon and the anterior facet of the femur⁽¹³⁾. It is proposed that pain of the lateral hip, known as greater trochanteric pain syndrome, is in most cases a result of pathology involving gluteal tendons or the iliotibial band. Fluid within bursae is secondary to these conditions, the primary trochanteric bursitis being very rare⁽¹⁴⁾.

Iliopsoas bursa is the largest bursa around the hip. For the assessment of the iliopsoas bursa pathology, the patient should be resting supine with 180° hip extension. The transducer should be positioned in the longitudinal plane, over the femoral head and femoral neck which are used as bony landmarks (Fig. 7A). The bursa should be seen between the musculotendinous part of iliopsoas muscle and the anterior capsule of the hip⁽¹⁵⁾ (Fig. 7B). Iliopsoas bursa communicates with the hip joint in 15% of adults⁽¹⁶⁾, and an enlarged bursa can be a consequence of hip pathology: osteoarthritis, inflammatory disease etc.⁽¹⁷⁾, or primary bursitis.

Fig. 7.

There are several bursae around the knee. They include prepatellar, deep and superficial infrapatellar bursae, and suprapatellar bursa anteriorly to the knee; Baker’s cyst in posterior knee compartment; medial collateral ligament bursa (Fig. 8), semimembranosus–medial collateral ligament bursa, and pes anserine bursa medially; lateral collateral ligament bursa, and iliotibial bursa laterally to the knee⁽⁵⁾.

Fig. 8.

During the embryological development, the suprapatellar bursa is divided from the knee joint with a thin septum or plica, but later the plica disappears, and it normally communicates with the knee joint in over 80% of adult individuals⁽¹⁸⁾. Suprapatellar bursa is situated between the intercondillar fossa of the femur and the quadriceps tendon.

For the sonographic evaluation of the suprapatellar bursa, the patient should rest in the supine position with 25–30 degrees knee flexion. The transducer should be positioned in the longitudinal plane, proximal to the upper pole of the patella used as bony landmark (Fig. 9). Suprapatellar bursa is enlarged in the majority of pathologic conditions affecting the knee and producing excessive fluid within the joint. Even small amounts of fluid in the suprapatellar bursa can be visualized by high-resolution ultrasound, which is comparable to MRI in the detection of fluid and synovitis both in the suprapatellar recess and the Baker’s cyst^(19,20). The quantity⁽²¹⁾, but also the quality of the effusion within the suprapatellar recess or the Baker’s cyst can be adequately assessed by ultrasonography⁽²²⁾. The fluid within the recess can be anechoic or hypoechoic (Fig. 10), hyperechoic, containing blood in cases of severe trauma or severe arthritis. Sometimes fat fluid level can be visible within the recess as a sign of intraarticular fracture⁽²²⁾ (Fig. 11).

Fig. 9.

Fig. 10.

Fig. 11.

Baker’s cyst is the normal gastrocnemius-semimembranosus bursa, in some adults communicating with the posterior part of the knee capsule through a thin neck⁽²³⁾ (Fig. 12A). Baker’s cyst is located between the semimembranosus and medial head of gastrocnemius tendons. To evaluate its presence and pathology by ultrasound, the patient should lie prone with a fully extended knee. The transducer should be placed in the longitudinal or transverse plane, in the medial half of the popliteal fossa, centered between the semimembranosus and medial gastrocnemius tendons which can serve as anatomic landmarks (Fig. 12 B).

Fig. 12.

Its presence is often related to knee effusion, and it occurs in about 40% of patients with mass lying posterior to the knee⁽²⁴⁾. The cyst enlarges frequently in cases of knee overuse, osteoarthritis of the knee, arthritis, pigmented villonodular synovitis, synovial osteochondromatosis (Fig. 12C) etc. Rupture of a Baker’s cyst with synovial fluid leakage in the calf is the most common and very painful complication. In case of Baker’s cyst rupture, there is a free soft-tissue fluid around the cyst visible on ultrasound.

Prepatellar bursa is normally a very thin structure, filled with a minimal amount of fluid, not visible on ultrasound. It is localized between the patellar surface and the proximal part of the patellar ligament and the skin.

For the sonographic assessment of prepatellar bursitis, the patient should rest supine, with the knee in partial (25–30 degrees) flexion. The transducer should be placed in the longitudinal position, over the inferior patellar pole which is used as a bony landmark (Fig. 13). Prepatellar bursitis, also known as housemaid’s knee is a common painful condition, easily visible sonographically (Fig. 14). In the majority of cases, it is a result of chronic overuse. Less commonly, it develops as a consequence of direct traumatic blow⁽²⁵⁾. Professions involving prolonged kneeling such as floor layers, carpenters, auto mechanics, housemaids and others are especially prone to prepatellar bursitis.

Fig. 13.

Fig. 14.

Superficial infrapatellar bursa is normally situated between the skin and the distal part of the patellar ligament. For the best representation of the superficial as well as deep infrapatellar bursa, the patient should lie supine, with a partially flexed (30 degrees) knee. The transducer should be in the longitudinal plane, following the fibrillar structure of the patellar ligament, just above the tibial tuberosity which could be used as bony landmark (Fig. 15). Superficial infrapatellar bursitis is also known as clergyman’s knee. In the majority of cases, it results from an acute traumatic injury (direct blow to the bursa) or chronic overuse⁽²⁶⁾ (Fig. 16).

Fig. 15.

Fig. 16.

Deep infrapatellar bursa is located between the inferior part of the patellar ligament and the anterior tibial surface (Fig. 15). Normal bursa in some situations can be visualized by ultrasound as a very small collection of anechoic fluid⁽²⁷⁾ posteriorly to the patellar ligament (Fig. 17). The etiology of the deep infrapatellar bursitis includes excessive sports activity, especially long-distance running and jumping (Fig. 18).

Fig. 17.

Fig. 18.

There are two clinically important bursae near the Achilles tendon⁽²⁸⁾. The deeper, retrocalcaneal bursa lies between the distal anterior part of the Achilles tendon and the posterosuperior part of the calcaneus. Normal retrocalcaneal bursa, which is a constant bursa, can be visible on ultrasound in almost 25% of healthy individuals⁽²⁷⁾. The superficial, or also called “Achilles”, bursa is situated between subcutaneous fat tissue and the distal Achilles tendon or the calcaneal surface.

In order to evaluate both bursae by ultrasound, the patient should lie prone, with feet hanging over the bed. The calcaneal tuberosity can be used as bony landmark for identifying the bursae. The transducer should be positioned in the longitudinal plane, following the Achilles tendon (Fig. 19).

Fig. 19.

The deep retrocalcaneal bursa is more commonly affected by various inflammatory diseases, traumatic and overuse injuries than the superficial Achilles bursa. Inflammation of the deep retrocalcaneal bursa combined with insertional Achilles tendinopathy, formerly known as Haglund “impingement” syndrome^(29,30), is a common type of bursitis (Fig. 20). The superficial retrocalcaneal bursa is an adventitial bursa that can form after birth as a result of chronic friction, usually in people wearing tight shoes⁽²⁹⁾.

Fig. 20.