X-ray diagnosis of osteoarthritis

Despite the rapid development in recent years of such modern methods of medical imaging as MRI, X-ray computed tomography, the expansion of the possibilities of ultrasound diagnosis, X-ray diagnosis of osteoarthritis remains the most common objective method of diagnosis and control of the effectiveness of osteoarthrosis treatment. This is due to the availability of this method, the ease of research, cost-effectiveness and sufficient information.

In general, x-ray diagnosis of osteoarthritis is based on the detection of narrowing of the joint gap, subchondral osteosclerosis and osteophy- roza (OF), the degree of narrowing of the x-ray joint gap being the main diagnostic value. On the radiographs of the joints can be determined areas of ossification of the joint capsule (late osteoarthritis). With the nodular form of osteoarthritis, the greatest diagnostic value is the detection of osteophytes, sometimes accompanied by a pronounced destruction of articular surfaces (the so-called erosive arthrosis).

The x-ray joint is filled with cartilage and an interlayer of synovial fluid that does not give an image on the radiographs, looks like a more transparent band between the articular surfaces.

The total thickness of articular cartilage on radiographs is determined by measuring the width of the X-ray joint gap between the joint surfaces of the epiphyses of bones. We will point out that the width of the x-ray joint gap has been used up to the present time as the main indicator in the diagnosis of osteoarthritis, and the standard radiograph of knee joints in the forward and lateral projections is recommended by the WHO and ILAR as a method of choice for assessing the dynamics of changes in articular cartilage during clinical trials of drugs. The narrowing of the x-ray joint gap corresponds to a decrease in the volume of the articular cartilage, and subchondral osteosclerosis and osteophytes at the edges of the articular surfaces are considered by most researchers as a response of the bone tissue to an increase in the mechanical stress on the joint, which in turn is the result of degenerative changes and a decrease in the articular cartilage volume. This is important not only for the diagnosis of osteoarthritis, but also for assessing the progression of the disease and the treatment.

These radiologic symptoms are considered specific for osteoarthritis and are included in the list of X-ray diagnostic criteria for the diagnosis of this disease, along with clinical ones.

Methods of optimization of X-ray diagnosis of osteoarthrosis

As already mentioned, methods for assessing the progression of osteoarthritis are based on the detection of radiological dynamics in the joints. It should be taken into account that the dynamics of x-ray changes in osteoarthritis differs by a slow rate: the rate of narrowing of the x-ray joint gap in patients with gonarthrosis is approximately 0.3 mm per year. The results of long-term studies of X-ray changes in patients with osteoarthritis in the knee joints receiving non-hormonal anti-inflammatory treatment showed no radiologic progression of the disease after 2 years of observation and minimal differences between groups of patients treated and control. The lack of reliable changes in long-term studies suggests that the radiologic symptoms of osteoarthritis with standard radiography of the joints remain relatively stable for a long time. Therefore, to assess the dynamics of changes, it is preferable to use more sensitive X-ray technologies, one of which is microfocus radiography of joints.

In microfocus X-ray machines, special X-ray tubes with a point source of radiation are used. Quantitative microfocus radiography with direct magnification of the image shows sufficient sensitivity to detect small changes in the structure of bones. With this method, the progression of osteoarthritis and the effect of the treatment can be recorded and accurately measured in a relatively short time between studies. This is achieved due to the standardization of the study and the use of radiographic measurement procedures, the improvement of the quality of the radiographs obtained with direct magnification of the image, which makes it possible to record structural details of bone that are invisible on standard radiographs. WHO / ILAR recommend measuring the width of the X-ray joint by hand using the Lequesne method using a magnifying lens and calculating the width of the x-ray joint at various points. Such measurements show that in repeated measurements, the coefficient of variation is 3.8%. The development of microcomputer and image analysis technology provides a more accurate assessment of joint anatomy changes than manual methods. Digital processing of the x-ray image of the joint allows you to automatically measure the width of the joint space with a computer. The mistake of the researcher is practically eliminated, because the accuracy with repeated measurements is established by the system itself.

From the point of view of prompt diagnostics, simplicity and ease of use, mobile X-ray diagnostic devices with a polyposition stand of the C-arc type, which are widely used in world practice, are of particular interest . Apparatus of this class allows you to conduct a patient examination in any projection without changing its position.

A method of functional radiography of the knee joints is worth mentioning, consisting of two consecutive x-ray photographs of the knee joint in the patient's position standing in the forward anterior projection with the predominant support on the limb being examined (1st image - with fully straightened knee joint, 2nd - with flexion under the angle of 30 °). The contours of the bone elements forming the X-ray joint slot from the first and second X-rays were transferred onto paper and the scanner was subsequently injected into the computer, after which the difference in the ratio of the lateral and medial areas between the first and second radiographs was determined by the degree of lesion hyaline cartilage of the knee joint (the stage of osteoarthrosis was evaluated by Hellgen). In the norm it was 0.05 + 0.007; for stage I - 0,13 + 0,006; for Stage II - 0.18 + 0.011; for stage III - 0.3 ± 0.03. There is a significant difference between the indices in the norm and in the 1st stage (p <0.001): between the I and II stages the difference is significant (p <0.05), between the II and III stage of osteoarthritis - significant difference (p <0.001).

The obtained indices testify that the x-ray planning of the knee joint with functional radiography objectively reflects the staging of osteoarthrosis of the knee joint.

The method of functional radiography with a load made it possible to establish that in 8 patients who had no pathological changes in traditional radiography, there is an initial decrease in the height of the x-ray joint gap. 7 patients had a more severe degree of lesion. Thus, the diagnosis was changed in 15 (12.9 + 3.1%) patients.

Along with the traditional method of radiographing the knee joint - examination of the knee joint in standard projections with a horizontal position of the patient - there is a technique for studying this joint in an upright position. According to A. Popov (1986), a picture of the knee joint, made in a horizontal position, does not reflect the real mechanical conditions of the joint in a state of weight load. He suggested conducting an examination of the knee in an orthostatic position with a predominant support on the limb being examined. SS Messich and co-authors (1990) expressed the opinion that the best position for the diagnosis of osteoarthritis is knee joint bending by 28 ° with the patient's vertical position also with the predominant support on the limb being studied, as biomechanical studies showed that the initial lesion of the hyaline cartilage of the knee joint is noted in the posterior sections of the condyles of the femur, which are at an angle of 28 ° in the sagittal plane, since it is in this position that the main time load acts on the chrome (physiological position of the knee joint). N. Petterson and co-authors (1995) proposed a method for radiographing a knee joint with a load in which the lower part of the shin is at an angle of 5-10 ° to the plane of the film and additionally the joint is bent at an angle of 10-15 °. In the authors' opinion, in this position the central ray is directed tangentially to the plane of the tibial condyle and the articular space will be correctly represented in the picture.

Thus, the purposeful use of the possibilities of classical radiography in view of clinical manifestations allows in many cases to confirm or at least to suspect the presence of damage to a certain structure of the ligaments and meniscus complex of the knee joint and to resolve the issue of the need for additional examination of the patient with other means of medical imaging.

X-ray symptoms mandatory for the diagnosis of primary osteoarthritis

The narrowing of the x-ray joint gap is one of the most important radiologic symptoms, having a direct correlation with the pathological changes occurring in the articular cartilage. The x-ray joint in the different parts of the joint has a different width, which is associated with an uneven decrease in the volume of articular cartilage in different parts of the joint surface. According to the WHO / ILAR guidelines, the width of the x-ray joint should be measured in the narrowest section. It is believed that in the pathologically altered joint this area experiences the maximum mechanical load (for the knee joint - it is more often medial parts, for the hip joint - upper medial, rarely - upper-lateral sections). Among the anatomical landmarks used to measure the joint gap on the radiographs of large joints are:

• for convex surfaces (head and condyles of the femur) - cortical layer of the terminal plate of the articular surface of the bone;
• for concave surfaces (the edge of the acetabulum, the proximal condyles of the tibia) - the edge of the articular surface at the base of the articular cavity.

Subchondral osteosclerosis is a consolidation of the bone tissue immediately located under the articular cartilage. Usually, this radiologic symptom - a consequence of friction of the naked articulating uneven joint articular surfaces of each other - is revealed in the late stages of osteoarthritis, when the joint slit is sharply narrowed. This symptom indicates a deep degenerative-destructive process in the articular cartilage or even the disappearance of the latter. The violation of the integrity of the articular cartilage, preceding its quantitative reduction, may be the result of densification of the cortical and trabecular bone tissue directly located under the cartilage. The compaction of the subchondral bone tissue in the area of the articular surfaces of the bones is measured at three equidistant points along the joint margin; The measurement results can be averaged.

Osteophytes - limited pathological bony outgrowths of various shapes and sizes that arise in the productive inflammation of the periosteum on the margins of the articular surfaces of bones - a characteristic roentgenological symptom of osteoarthritis. In the initial stages of development of osteoarthritis, they have the form of cusps or small (up to 1-2 mm) osseous formations at the edges of articular surfaces and at the sites of attachment of their own ligament joints (in the knee joints - along the edges of the intercondylar tubercles of the tibia, at the attachment of cruciate ligaments; hip joints - at the edges of the fossa of the head of the femur, on the medial surface of the femur, at the place of attachment of the own ligament of the head of the femur).

As the severity of osteoarthritis increases and the narrowing of the joint gap progresses, the osteophytes increase in size, take different forms in the form of "lips" or "ridges", rectilinear or "magnificent" bone growths on a wide or narrow base. In this case, the articular head and cavity can significantly increase in diameter, become more massive and "flattened". The number of osteophytes can be counted separately or in total in both joints, and their dimensions should be determined by width at the base and length. The change in the number of osteophytes and their size is a sensitive indicator of the progression of osteoarthritis and monitoring the effectiveness of its treatment.

X-ray symptoms, not necessary for diagnosis of primary osteoarthritis

Periarticular margin defect of bone tissue. Although this radiographic symptom, which can be observed in osteoarthritis, was defined by RD Altman and co-authors (1990) as "joint surface erosion", the term "periarticular border defect of bone tissue" is more preferable, since there is as yet no precise histological characterization of these radiologically detectable changes. Boundary defects of bone tissue can be detected in the early stages of osteoarthritis, and their appearance can be caused by inflammatory changes in the synovial membrane. Similar changes are described in the large joints and in the joints of the hands. Usually, with osteoarthritis, these defects are of small size, with a site of osteosclerosis at the base. In contrast to the true erosions revealed in rheumatoid arthritis, which do not have sclerotic changes at the base and are often determined against the background of periarticular osteoporosis, the bone tissue surrounding the periarticular margin defect is not dilated in osteoarthritis.

Subchondral cysts are formed as a result of resorption of bone tissue in the region with high intra-articular pressure (in the place of the greatest load on the joint surface). On the roentgenograms they have the form of ring-shaped defects of the trabecular bone tissue in the subchondral bone with a clearly defined sclerotic rim. Most often subchondral cysts are located in the narrowest part of the joint gap and arise when the disease worsens. They are characteristic for osteoarthritis of the hip joints, and can be found both in the head of the femur and in the roof of the acetabulum. The dynamics of changes in subchondral cysts is judged by their number and size.

Intra-articular calcified chondromas are formed from areas of necrotic articular cartilage, and can also be a fragment of bone tissue (osteophytes) or produced by the synovial membrane. Usually they reach small sizes, located between the articular surfaces of bones or on the side of the epiphyses of bones, have different shapes (rounded, oval, elongated) and uneven speckled structure, which is caused by the deposition of calcium-containing substances in the cartilaginous tissue. In the joint, usually no more than 1-2 chondromes are found.

In the knee joint for the calcified chondroma, it is possible to take the sesamoid bone (fabella) in the popliteal fossa, which also changes its shape, position and size in the osteoarthrosis of the knee joint. De formation fabella is one of the symptoms of osteoarthritis of the knee.