Ultrasound of articular bags

The joint bag is a bag containing synovial fluid. More often they settle down in a place of an attachment of tendons, under a tendon above a bone. Articular bags are divided into communicating with the cavity of the joint and non-communicating. The most common are noncommunicatory. Also, articular bags can be divided into superficial (subcutaneous) and deep.

Method for the study of articular bags.

The choice of the sensor depends on the type of joint bag being examined. For surface it is better to use a sensor with a frequency of 10-15 MHz and a large amount of gel. For deep - from 3 to 7.5 MHz, depending on the constitution of the patient. Comparison with the contralateral side helps in estimating the amount of synovial fluid inside the bag. The largest bag is subacromial-sublantoid, located deep beneath the deltoid muscle. Some of the articular bags are directly connected to the joint cavity, such as a suprapatellar sac or a superficial patella or an elbow bag.

Localization and types of articular bags

Bag type	Localization	Name of bag
Subcutaneous	Elbow	Bag of elbow
	Hip	Subcutaneous bag of large spit
	Knee	Prepatellar, subcutaneous podadikolennikovaya, subcutaneous bag of tuberosity of the tibia
	Ankle	Subcutaneous Achilles tendon bag
	Foot	Finger pouch of the first finger
Deep	Shoulder	Subacromial, subldeloid, subscapular (in 50% of cases may have a connection with the joint)
	Hip	Internal blocking, ilio-lumbar (may have a connection with the joint), deep vertebral
	Knee	The bag of the iliac-tibial tract, the fibula of the lateral ligament, the lateral ligament of the lateral ligament, the subfascial prepatellar, the deep podadalennikovaya, the popliteal bag (can have a connection with the joint), the gastrocnemius-semimembranous (may have a connection with the joint), the supracatellar (may have a connection with the joint )
	Ankle	Over-the-shoulder bag

Echocardiitis of the articular bags is normal.

Normally, the cavity of the joint bag looks like a thin hypoechoic band about 1-2 mm thick, surrounded by hyperechoic lines - the walls of the bag. Normally, the supracarial bursa contains about 3-5ml of fluid. Pushing the lateral parts of the bag towards the center can improve the visualization of the bag.

Ultrasound signs of the pathology of the articular bags.

Bursitis is an inflammatory reaction in the joint bag. The degree of inflammatory reaction can be from the minimal, in the form of synovitis, to abscess formation. Echocardiitis depends on the presence or absence of the connection of the joint bag with the joint cavity. Treatment consists in restriction of movements in a joint. Sometimes anesthetics and corticosteroids are injected into the joint bag to reduce the inflammatory response of the synovial membrane.

The pathology of articular bags, non-communicating with the joint cavity.

Acute posttraumatic bursitis. The mechanism of bursitis development is a recurrent trauma. It arises as a protective reaction with frequent traumatization of the joint. With acute bursitis, the volume of the joint bag increases, anehogenous contents appear. The walls of the bag are thin, which is the defining feature when differentiating with chronic bursitis. The most typical localizations of acute bursitis are: prepatellar bag, deep podnadkolennikovaya bag, Achilles tendon backpack, elbow bag, subcutaneous bag of large trochanter of femur.

Chronic posttraumatic bursitis. It develops at constant elevated loads on a certain anatomical area. With chronic bursitis, in contrast to acute bursitis, the walls of the bag are thick. The contents can be anechogenous, hypo-or hyperechoic with the presence of fibrous septa. Hyperechoic calcifications can be detected against the background of the contents of the bag. Women often develop chronic bursitis of a metatarsal bag of 1 finger, which is caused by wearing too tight shoes.

Hemorrhagic bursitis. Causes are different: from simple trauma, rupture of the adjacent tendon, fracture of the bones to increased bleeding and disturbance of the hemostasis system. At the same time, the articular bag is enlarged in size larger than with simple acute bursitis, which resulted from excessive loading. In the acute period, the echostructure of the contents of the bag is uniform due to the finely dispersed suspension, in the future it becomes non-uniform, due to the presence of echogenic clots, fibrin filaments and anehogenous fluid.

The pathology of the articular bags communicating with the joint cavity.

Effusion in the joint bag and intra-articular pathology. The connection of the joint bag with the joint cavity develops gradually and is often observed after 50 years. For example, iliac-lumbar bursitis with aseptic necrosis of the femoral head or the emergence of Baker's cysts (gastrocnemius-semimembranous bursitis) in athletes. The connection of the subacromial bursa with the shoulder joint appears only when the rotator cuff ruptures.

The appearance of fluid in the subacromial bag may serve as an early sign of impingement syndrome.

In ultrasound examination, it is possible to identify the connection of the bag with the joint through a narrow channel, for example, with Baker's cysts at the medial edge of the popliteal fossa.

The increase in articular bags in size may be a manifestation of a number of pathological conditions and joint diseases: dissecting osteochondritis, osteonecrosis, osteoarthritis, cartilage plate defects, meniscus damage, intraarticular body ("articular mouse"). With all these diseases, the fluid in the bag is anechoic. Tears occur in rheumatoid bursitis.