Diagnosis of osteoarthritis: ultrasound (ultrasound) of the joints

The use of ultrasound (sonography) in rheumatology is a relatively new and promising direction. In the last decade, ultrasound (US) has become widely used as a visualization technique for examining patients with rheumatic joint diseases, as well as for monitoring treatment. This has become possible due to the improvement of computer technology and the development of higher-frequency sensors. Sonography is usually used to assess soft tissue pathology and detect fluid, but it also allows visualization of cartilage and bone surfaces.

A number of undoubted advantages - non-invasiveness (unlike arthroscopy), availability, simplicity, cost-effectiveness (in comparison with CT and MRI) - have provided the ultrasound method of the musculoskeletal system with priority among other instrumental methods for examining joints and soft tissues. Ultrasound is highly informative in reflecting small details of the bone surface, ligament-tendon apparatus, and also allows identifying and monitoring inflammatory changes in tissues. Another advantage of ultrasound over the X-ray method is that the position of the sensor is determined exclusively by the goals set by the researcher, therefore, unlike X-ray, there is no need for strict positioning of the patient to obtain standard projections, i.e. the sensor can be multi-positional. When conducting an X-ray examination to visualize certain structures in standard projections, it is often necessary to take pictures several times, which leads to an increase in the examination time, additional consumption of materials (film) and irradiation of the patient and laboratory personnel. The main disadvantages of ultrasound include the inability to visualize the structure of bone tissue, the subjectivity of the assessment of the data obtained.

In connection with the above, it is very important to correctly use the capabilities of ultrasound to identify pathological changes in various joints and soft tissues, for which it is necessary to know not only the capabilities of modern diagnostic equipment, but also the ultrasound anatomy of the area being examined and the most typical manifestations of the disease.

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Equipment and methods for performing ultrasound

Ultrasound of soft tissues and joints should be performed using a high-frequency linear transducer operating in the range of 7-12 MHz. The use of a transducer with a lower operating frequency (3.5-5 MHz) is limited to examination of the hip joint and examination of joints in obese patients. It is also important to select the correct examination programs for different joints. Many ultrasound devices already today contain a set of standard programs for examining various parts of the musculoskeletal system. Modern ultrasound devices are also equipped with a large number of additional scanning modes that significantly expand the diagnostic capabilities of conventional gray-scale scanning, such as native or tissue harmonic mode, panoramic scanning mode and three-dimensional reconstruction mode. Thus, scanning in the native harmonic mode allows you to obtain a more contrasting image of delicate hypoechoic structures reflecting ligament or meniscus rupture zones than with conventional gray-scale scanning. The panoramic scanning mode allows obtaining an expanded image of several structures at once, for example, the structures forming a joint, and displaying their spatial arrangement and correspondence. Three-dimensional reconstruction provides not only volumetric information, but also makes it possible to obtain multiplanar sections of the structures under study, including frontal ones. The use of high-frequency ultrasound sensors, which provide the ability to visualize structures of varying echogenicity and depth, is fundamentally new. These sensors have significantly increased the resolution in areas close to the sensor while simultaneously increasing the penetrating power of the ultrasound beam. They use a narrow ultrasound beam operating in the high-frequency range, which contributes to a significant increase in lateral resolution in the ultrasound focus zone. The capabilities of ultrasound scanning have also expanded significantly due to the introduction of new ultrasound technologies based on the Doppler effect into practice. New ultrasound angiography techniques make it possible to visualize pathological blood flow in the area of inflammatory changes in organs and tissues (for example, with synovitis).

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Artifacts arising during ultrasound examination of the musculoskeletal system

All artifacts that arise during ultrasound examination of the musculoskeletal system are divided into standard ones, which arise during all ultrasound examinations, and specific ones, which are characteristic of ultrasound examination of ligaments and tendons.

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Artifacts arising from ultrasound beam refraction

A distal shadow may appear at the edges of rounded structures at the interface of two different acoustic environments. Normally, this effect can be observed during transverse scanning of the Achilles tendon. Intramuscular septa may also produce a shadow behind them. An amplification effect of the ultrasound signal occurs behind fluid structures. Therefore, structures located behind fluid-containing objects may appear more echogenic than normal. For example, the presence of a small effusion in the synovial sheath of the tendon increases its echogenicity.

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Reverberation

This effect can occur behind highly reflective objects such as bone, diaphragm, resulting in mirror or phantom images. In musculoskeletal examinations, this effect can be observed behind the fibula. Metal and glass objects cause a reverberation effect called a "comet tail". As a rule, in the examination of musculoskeletal organs, it can be observed in the presence of metal prostheses or metal (glass) foreign bodies.

Refraction

Refraction occurs at the boundary of reflective media with different sound conductivity (e.g., fatty tissue and muscles) as a result of refraction of the ultrasound beam, which leads to dislocation of the structures being imaged. To reduce refraction, hold the sensor perpendicular to the structures being examined.

Anisotropy

Anisotropy is an artifact specific to ultrasound examination of the musculoskeletal system that occurs during ultrasound scanning of tendons with a linear transducer when the scanning ultrasound beam does not fall on them strictly perpendicularly. In the area of the tendon where there is no exact perpendicular reflection of the ultrasound beam, zones of reduced echogenicity will appear that can simulate the presence of pathological changes. Muscles, ligaments and nerves also have a weak anisotropy effect. A decrease in the echogenicity of the tendon leads to a deterioration in the quality of visualization of its fibrillar structure. However, in some cases, when it is necessary to visualize the tendon against the background of echogenic tissue, by changing the scanning angle, the tendon will look contrasting (hypoechoic) against the background of echogenic fatty tissue.

Degenerative-dystrophic changes in osteoarthrosis of other joints are also echographically manifested by narrowing of joint spaces, reduction in cartilage height, changes in periarticular soft tissues and bone articular surfaces with the formation of osteophytes during long-term progression, as occurs with gonarthrosis or coxarthrosis, so we will not dwell on them in detail.

Thus, ultrasound has advantages over traditional radiography in the early detection of local changes in the joints and periarticular soft tissues of patients with osteoarthritis.

An example of an ultrasound protocol for a patient with gonarthrosis:

Articular relationships are preserved (impaired, lost), without deformation (flattened, deformed). Marginal bone growths of the femur and tibia are not determined (they are up to... mm, localization). The superior recess is unchanged (expanded, with the presence of excess homogeneous or heterogeneous fluid, the synovial membrane is not visualized or thickened). The thickness of the hyaline cartilage in the area of the patellofemoral joint, lateral and medial condyle is within the normal range up to 3 mm (decreased, increased), uniform (uneven), the structure is homogeneous (with the presence of inclusions, description). The contours of the subchondral bone are unchanged (uneven, with the presence of cysts, superficial defects, erosions). The integrity of the quadriceps muscle of the thigh and the patellar ligament is not damaged, ligg.collaterales are not changed, the integrity of the fibers is preserved (ultrasound signs of partial damage or complete rupture). The anterior cruciate ligament is not changed (there are signs of calcification). Menisci (external, internal) - the structure is uniform, the contours are clear, even (ultrasound signs of damage - fragmentation, calcification, etc.).

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