X-ray diagnosis of osteoarthritis of the knee (gonarthrosis)

Knee-joint - one of the most difficult joints for proper radiographic examination because of their structural complexity and the wide range of movements. Osteoarthritis can be localized only in a certain section of the joint, which is also difficult to diagnose articular changes in osteoarthritis of the knee (gonarthrosis).

Anatomical and biomechanical characteristics of the knee initially suggest a significant rate of destruction not only bone structures but also the meniscus ligament-Complex (SMC). Therefore, a high percentage of primary diagnostic errors in the analysis of radiographs can be explained by the fact that only focuses on changes in bone structure. Analyze and on the basis of certain characteristics to assume with high probability the presence of QMS damage during radiography enable numerous functional tests and installation. In view of changes detected X-ray examination may be supplemented by other imaging methods - ultrasound, MRI, and others.

The basic rule under X-ray examination of the knee joint is polypositional.

The standard projections, applied at the knee X-rays are straight (anteroposterior) and side. As necessary, they are supplemented with the right or left oblique, and axial and other projections.

The effectiveness of X-ray of the knee lesions is largely dependent on the quality of radiographs.

The direct projection of the contours of the inner and outer slits roentgen of joint have different curvature and orientation, so that they can not be obtained as a perfect single line on the same image. The inner part is better seen when the central X-ray beam is perpendicular to the surface of the table and the outside - when kaudokranial offset beam at 5-7 °. The compromise is achieved, depending on the zone of interest. The axis of rotation passes through the medial knee joint area, which is so often undergoes changes as compared to the outside. Therefore, when performing knee shot to the direct projection of the preferred considered laying, when the joint is in a state of maximum extension from the perpendicular direction of the central beam to the object of study and centration on its midpoint knee slightly offset inwards.

The image formed in the position of maximum extension of the knee, is standard anteroposterior projection. It allows you to explore the front part roentgen of joint gap.

Direct pictures taken when bending the knee in the to 30 ° (laying Shussa) or 45 ° (laying Fick), made for the assessment of the hind sections roentgen of joint gap, at which most often found damage to the subchondral bone sections (osteonecrosis) and cartilaginous structures ( osteochondritis).

These are suitable for stacking study intercondylar space, which in this position is the most affordable review and allow the identification of free foreign bodies in the joint cavity, formed as a result of damage to the articular cartilage.

The picture of the knee in a straight line projection can be performed in the position of a patient lying down and standing up. When the pathology has a mechanical nature and expected to damage ligaments, it is preferable to perform X-ray standing both in load and in a relaxed state for research roentgen of joint gap and joint axis.

X-rays of the knee in a straight line projection necessarily complemented image in lateral projection.

At the side of the central X-ray beam passes through the joint space with a slope of 10 ° to the direction kaudokranial. Thus femoral condyles edges overlap and their joint surfaces are displaced posteriorly bottom. This allows them to distinguish between good contours and assess the state of the PFD joint.

The picture of the knee joint in the lateral projection is carried out either with the patient lying on his side, with full joint relaxation or standing, with no load on the investigated joint. Easy knee flexion (30 ° or 15 °) allows you to determine the status of the VFD joint. Flexion is intended for visualization of the patella at the time of its introduction into the intercondylar region.

Carrying out radiography in lateral projection reveals transient instability (entry delay patella in the intercondylar fossa) that can disappear at 30 ° flexion or not detected on the axial image, when the minimum bending is 30 °, as well as to estimate the height of the patella and the state of its articular surface.

Different areas of the joint surface of the knee on the side picture are the characteristic features. These differences are related to the functional characteristics of each site. The shape of the condyles of the femur is a mirror picture of the front of the corresponding tibial plateau, which is contacted with an extreme extension of the knee.

In the presence of transient patellar instability or suspected damage to the cruciate ligament is necessary to conduct additional stress tests.

Especially great is the importance of the side image for studying the PFD joint.

In assessing the topography of the patellar apply different measurement factors, of which the most used - index Cato. To measure this index picture is required, produced by bending the knee at 30 °.

Cato's index is the ratio of the distance from the bottom edge of the patella to the anterior tibial angle (a) to the length of the articular surface of the patella (b). Normally, this ratio is usually equal to 1.0 ± 0.3.

Too high position of the patella (patella alta) causes a delay in its implementation trohleary in the mouth that can cause suprapatellaris-femoral instability. For the diagnosis of such instability is used suprapatellaris index.

On the picture side profile of the patella has two rear lines, one of which corresponds to the ridge of the patella, and the other, more dense - its outer edge. The distance between the two lines (a-a) and is suprapatellaris index (OK - 5 mm). The values of <2 mm indicate instability, which may, however, be transient, disappearing when bent over an angle of 15-30 °.

Trohlear index is measured from the bottom of the intercondylar fossa to the articular surface of the patella, namely to its ridge, and is determined at 1 cm from the upper edge of the intercondylar surface that corresponds to the introduction zone at the beginning of the patella flexion. Normally, it should be 1 cm. The values of <1 cm show dysplasia of the patella, which is often associated with hypoplasia of the articular surface of the patella. For large values of the index should not think too much about the depth of the intercondylar fossa, which increases the risk of developing patellar chondropathy.

A certain role in the diagnosis of lesions of the knee joint is given patellofemoral axial projection.

Radiography at 30 ° flexion of the most informative to study roentgen of joint gap PFD. With less bending the thickness of soft tissue through which the beam is high, which adversely affects the image quality. This axial projection is different, with a large flexion angle, visualization of edges trohleary clippings. The inner edge of the intercondylar fossa is very short, the inner and outer edges have an angular appearance, much sharper than in the lower and middle segments trohlei. The outer part of the joint is subjected to the PFD greater stress than the inner. Therefore, subchondral bone is thicker at the outer portion and the bone trabeculae are oriented outwards.

Axial shot at 30 ° C is most useful for detecting instability of the patella (external transient subluxation of the patella occur only at the beginning of flexion) and primary osteoarthritis of the lateral joint PFD.

Traditionally, to determine the radiological stage of osteoarthritis of the knee used classification I. Kellgren and I. Lawrence (1957), M. Lequesne improved in 1982, based on an assessment of the severity of the narrowing gap roentgen of joint, subchondral osteosclerosis and bone growths boundary values, there stand 4 stages.

osteoarthritis step (Kellgren I. and by Lawrence L, 1957)

• 0 - No radiological signs
• I - Doubtful
• II - Minimum
• III - Medium
• IV - Severe

Despite a certain conventionality of this division of osteoarthritis on radiographic stage, this technique has been used successfully in the modern radiology under certain conditions. In particular, for the early detection of gonarthrosis is necessary to investigate the joint in three projections: front, side and axial, which allows to evaluate the medial, lateral, PPO and joint TFO.

For a more accurate assessment of radiographic changes for osteoarthritis A. Larsen (1987) proposed a more sophisticated methodology to quantify the severity of osteoarthritis.

Criteria for osteoarthritis (Larsen A., 1987)

• 0 - No radiological signs
• I - rentgenosustavnoy narrowing gap less than 50%
• II - rentgenosustavnoy narrowing gap of more than 50%
• III - Weak remodulation
• IV - Average remodulation
• V - Severe remodulation

Early radiological signs (corresponding to stage I-II osteoarthritis according to Kellgren):

• stretching and sharpening edges intercondylar eminence of the tibia (at the site of attachment of the cruciate ligament);
• a slight narrowing of the joint space (most often in the medial joint department);
• sharpening the edges of the articular surfaces of the condyles of the femur and tibia, often in the medial joint department (associated with a greater load on the joint department), especially in the presence of varus deformity; at least - in the lateral parts, or simultaneously on both halves of the joint surface.

Radiographic signs of progression of osteoarthritis of the knee (corresponding to stage III-IV osteoarthritis by Kellgren):

• increase roentgen of joint narrowing the gap;
• development of subchondral osteosclerosis in the most loaded part of the joint;
• The emergence of multiple large osteophytes on the sides, front and rear edges of the articular surfaces;
• subchondral cyst (rarely found);
• Secondary synovitis with development sub patellar or popliteal cyst Baker;
• flattening and unevenness of the articular surfaces of the femur and the tibia, the loss of their anatomical and functional differentiation;
• a multi-faceted irregular shape sesamoid bones (fabella);
• possible detection of calcified chondroma;
• possible development of aseptic necrosis of bone condyles (rare).

Quite often osteoarthritis of the knee appears in the form of osteoarthritis

PFD (almost always external, sometimes internal and external, internal only rarely).

Outdoor osteoarthritis of the knee usually appears at the beginning of its development at the level of the upper cartilage sector intercondylar groove and the bottom of the patella cartilage sector corresponding to the part of the knee joint, which is rendered in this projection. The maximum load on the subchondral bone sections noted in the beginning of the flexion of the knee, at the moment when the patella begins to enter the intercondylar fossa. Therefore, changes in the joint PFO are quite common, but, as a rule, rarely diagnosed in time. The main cause of delayed diagnosis is that in practice the axial radiographic projections are not used sufficiently. Consequently, the direct X-ray of the knee must always complement the impact image of the patella in the lateral or axial projection.

By radiographic signs of osteoarthritis of the knee in the lateral and axial projections include:

• roentgen of the joint narrowing the gap between the patella and the femur;
• PF on the rear corners of the patella and the condyles of the femur;
• patellar subchondral osteosclerosis;
• isolated subchondral cysts with sclerotic rim. It should be noted that there are three stages radiographically osteoarthrosis

Subchondral osteo-condensing and increased trabecular pattern of the outer edge of the patella, experiencing the greatest external loads ( "hyper pressure syndrome") correspond to the I stage of osteoarthritis. In stage II there is infringement (local narrowing) of the joint space, even in the absence of patellar subluxation. Stage III of the knee osteoarthritis is characterized by the almost complete disappearance of roentgen of the joint slit seal subchondral cortical layer, which are formed in the interior of the vacuum sections - cortical surfers, and the emergence of perichondral osteophytes beak formations. Identification of marginal osteophytes allows the patella with a high degree of reliability assumed damaged articular cartilage. Having them on the outer and inner contours of the femoral condyles and tibial bones indicates damage to the meniscus corresponding side. Severe osteoarthritis most often occurs when the axis of displacement of the patella due to its external subluxation resulting from dysplasia or disorders of articular joint relationship PFD.

Using the axial image at 30 ° C can also be calculated Bernazho index - the distance between the anterior tibial tuberosity and the intercondylar fossa, which normally ranges from 10 to 15 mm. Reducing or increasing this distance usually indicates dysplasia femoral condyle or patella, resulting in instability of the joint PFD.

Study roentgen of the joint gap PFD when bending the knee at 60 ° and 90 ° allows a detailed study of the middle and lower part of  between condylar space and the upper part of the patella. Usually, pathological changes in these areas are observed later than in the upper sections of the intercondylar fossa.

Standard evaluation of radiographs of joints on the Kellgren and Lawrence suitable mainly for use in routine clinical practice. In clinical and epidemiological studies often require more detailed classification of the severity of osteoarthritis. For this purpose, the height of the joint space of the knee joint is measured TFO thin plastic ruler graduated in 0.5 mm or calipers. This quantitative assessment is more accurate, to use a special X-ray and computer program processing.

J.C. Buckland-Wright et al (1995) proposed to measure the height roentgen of the joint gap (in mm) on close-up radiographs knee joints in the outer, middle and inner thirds TFO medially and laterally.

Obviously, in the evaluation of radiographs of patients with osteoarthritis of the joints can not be limited to the height of the joint space research, however more preferred are semi-quantitative evaluation technique, which is widely used in large-scale clinical and epidemiological studies. All of these techniques have the general principle - the most important symptoms of radiological osteoarthritis (the height of the joint space, osteophytosis, subchondral sclerosis, subchondral cysts) were scored either in degrees (typically from 0 to 3).

One of the first semi-quantitative assessment of proposed knee radiographs Abask S. (1968). According to this method, the above four criteria radiological osteoarthritis evaluated on a scale from 0 to 3 and PFD TFO. The main disadvantages of this scale are: the lack of assessment of the PFD of the knee joint and the high probability of an ambiguous interpretation of radiological symptoms by different users. A similar system developed R.D. Altaian et al (1987). Considering the main drawback of these two systems (score only TFO knee joint), TD. Spector and colleagues (1992) proposed a method for semiquantitative evaluation of radiographs of the knee in the projection of «sunrise», which allows you to optimally explore the PFD. The "Atlas of radiographic osteoarthritis» S. Barnett et al (1994) to the joint assessment of PFO in the projection of «sunrise» added assessment in the standard lateral projection.

We propose a method of semi-quantitative assessment of the progression of gonarthrosis:

We propose a method of semi-quantitative assessment of the progression of coxarthrosis:

1. Reducing the height of the joint space:

• 0 - no,
• 1 - slight,
• 2 - moderate,
• 3 - a complete obliteration of the interosseous space;

2. Osteophytes:

• 0 - no,
• 1 - 1-2 small osteophytes
• 2 - one large or 3 small osteophyte and more
• 3 - 2 large osteophyte and more;

3. subchondral cysts:

• 0 - no,
• 1 - 1-2 small cysts,
• 2-1 large or 3 small cysts or more 3 - 2 large cysts and more;

4. subchondral sclerosis:

• 0 - no,
• 1 - minor, local (in the medial or lateral part of the joint TFO or PPO)
• 2 - moderate,
• 3 - significantly expressed circulated.

R.D. Altman et al (1995) were combined in a single system of semi-quantitative assessment of both the knee and departments have published "Atlas of individual radiographic signs of osteoarthritis," which received the second name "Atlas ORS». The advantages of this system can also include the fact that it shows the real X-ray of the knee with osteoarthritis. In addition, the "Atlas of ORS» has a number of drawbacks. Among them are the following:

• joint space narrowing graduation and increase the size of osteophytes have unequal intervals,
• on certain x-ray of the knee presents rare types of osteophytes,
• the quality of X-rays varies, making it difficult to compare them,
• presence of several radiological symptoms (joint space narrowing, osteophytosis etc.) On the same X-ray, making it difficult to work with "Atlas" and can lead to a biased assessment of real radiographs,
• a large volume of "Atlas", which complicates its use.

Y Nagaosa et al (2000) took into account the shortcomings of previous systems of semiquantitative evaluation of radiographs of the knee and developed their atlas, illustrative material which is a graphical representation of the contours of the knee joint components in direct projection (TFO joint) and in the projection of «sunrise» (joint PFO) . An important advantage of the system Y Nagaosa et al is not only that they are separately considered medial and lateral part of the TFO and the PFD of the knee, but the fact that radiographic signs of osteoarthritis are presented separately for men and for women.

In a study of 104 patients with osteoarthritis of the knee authentic (according to ACR criteria, 1990), we studied the size and direction of growth of osteophytes and evaluated the possible relationship between their size and other radiological data having connection with the growth of osteophytes.

Standard radiographs were analyzed both knee joints (except in patients undergoing arthroplasty or removal of the kneecap). Radiological gonartrosis was defined as the presence of a uniform or non-uniform narrowing roentgen of the joint gap and marginal osteophytes (ACR criteria, 1990). X-ray of the knee was performed in standard projections: anteroposterior with full extension of the lower limbs and the axial.

When evaluating radiographs of the knee joint conditionally divided into sections according to the current recommendations: TFO lateral and medial, lateral and medial PFD. Narrowing roentgen of the joint slit in each of these departments, as well as the size of osteophytes on each of the 6 areas: lateral and medial articular surface of the femur (or LB and MB), the tibia (LBB and MBB), patella (LN and MN) as well as osteophytes, lateral and medial femoral condyle (LW and MW) were evaluated on a scale from 0 to 3 according to the certification system Logically derived line drawing atlas for grading of knee osteoarthritis. osteophytes growth direction is visually divided into 5 categories - up (bottom-up growth), up lateral, laterally, down laterally or down (falling growth).

Violation of the cortical layer of bone (local deformation or "wear" the bones) and chondrocalcinosis in TFO and PFO was assessed by 2-point scale (0 - absent 1 - present). Tibiofemoral angle varus deformity indicator was estimated at anteroposterior projection. Subluxation of the patella on knee pictures in axial projection medially estimated 0-1, 0-3 laterally. Roentgen of the joint Narrowing the gap in each department studied and lateral subluxation of the patella were also respectively divided into 0-3 degrees.

In 92 patients found a close correlation between the X-ray of the right and left knee.

Osteophytes were detected in all investigated areas, and were marked by various forms and directions of growth.

Similar patterns were observed in the analysis of the direction of growth of osteophytes, depending on the degree of local joint space narrowing. In LB, MB, MBB, LM severity local narrowing gap has been associated with the direction of the growth of large osteophytes. osteophyte growth direction in LBB was not due to the size of osteophytes and a local narrowing of the joint space lateral and medial TFO, but it is not correlated MH any osteophytes size nor to the degree of the local constriction.

The positive correlation between the size of osteophytes, and the degree of local joint space narrowing was observed in all departments except the medial PFD. In the latter the size of the patellar osteophytes and MM positively correlated with the gap narrowing medial TFO. The size of osteophytes in the LB and LBB lateral TFO positively correlated with the degree of narrowing of the lateral PFD.

To clarify the relationships between some of radiographic and clinical data with the size of osteophytes latter were analyzed using multivariate analysis.

Local narrowing of the gap was due to the presence of osteophytes in most of the analyzed sites. Osteophytes in LBB were associated with the narrowing of the gaps of the medial and lateral TFO PFD. Osteophytes in the LN and LM correlated more with lateral subluxation of the patella than the local constriction. Grade 2-3 medial osteophytes PFO is not associated with a local narrowing, but are associated with varus deformity and narrowing the gap medial TFO. The degree of local deformation TFO was associated with the presence of osteophytes 2-3 degrees in the lateral and medial TFO.

Factors associated with the presence of osteophytes, depending on the size of the last above) in both lateral TFO and (osteophytes 2-3 tbsp.) In the lateral PPO. Chondrocalcinosis was caused by the growth of osteophytes at many sites. The presence of lateral subluxation of the patella is closely correlated with the growth of osteophytes in the lateral PFD and varus deformity - the presence of osteophytes 2-3 degrees in the medial TFO. The total number of osteophytes correlated with the number of osteophytes in MB and MM.

Dimensions of growing towards each other osteophytes in the same division were correlated in all of the analyzed sections: the correlation coefficient was 0.64 g for lateral TFO, 0.72 - for medial TFO, 0.49 - for lateral PFD 0.42 - for medial PFD.

Therefore, in all parts of the knee, in addition to LBB and MN, the direction of growth of osteophytes varies with the size of the latter and the degree of joint space narrowing. The observed correlation supports the hypothesis of the influence of both general and local biomechanical factors on the formation of osteophytes. The effect of the last shows we observed a correlation between parameters such as:

• size of osteophytes in the medial PFD and narrowing the gap medial TFO;
• LBB size of osteophytes and narrowing of the gap as the TFO medial and lateral PPO;
• size of osteophytes in the lateral PFD and lateral subluxation of the patella;
• size of osteophytes, medial TFO and PPO and the presence of the varus deformity. In contrast, the analysis chondrocalcinosis bonds to the total number detected osteophytes opposite changes.

It can be assumed that the local instability - an important starting biomechanical mechanism of formation of osteophytes. In animal models of osteoarthritis demonstrated that the formation of osteophytes at joint instability accelerated by movements in the joints, and slows down when immobilized. As noted L.A. Pottenger et al (1990), the surgical removal of osteophytes during knee arthroplasty in patients with osteoarthritis leads to a worsening of the instability in the joint, which is indicative of the stabilizing role of osteophytes in this pathology. Our observation that the lateral growth osteophyte increases the surface area of the loaded articular confirmed the data obtained J.M. Williams and K.D. Brandt (1984). For small osteophytes dominant growth direction - lateral (LBB except where osteophytes grow mainly upwards, provided that the gap is narrowed TFO medial and lateral TFO minimally involved in the process). LA. Pottenger et al (1990) showed that even vertical osteophytes may stabilize the joint, probably by creating a surface newly formed bone and tibial valgus limit excessive motion. Unlike small it grows large osteophyte preferably upwards or downwards. This phenomenon may reflect anatomical limitation "lateral" growth adjacent periarticular structures or compensatory enlargement processes and mechanical reinforcement base osteophyte to prevent sprains.

Among these compensatory changes should also mention the so-called high tide lines, representing calcification zone connecting the hyaline cartilage with subchondral bone. Normally, they are wavy and thus effectively counteract the considerable stress. In osteoarthritis due to the fact that the cartilage is destroyed, and a new cartilage formed as osteophytes, this area is rebuilt. Consequently, one of the manifestations of osteoarthritis is the presence of multiple high tide line. Since the exposed articular surface of the bone, it becomes a compensatory mechanism for the formation of dense sclerosis (eburnation), often associated with the formation of deep grooves (indentations). The latter are particularly often found in the knee joint (PFD), which can be considered as a means of stabilizing the joint, providing its "rails". These grooves are well visualized on axial images of PFO in patients examined by us.

A close correlation was observed between the size of osteophytes and local thinning of cartilage, especially in the medial and lateral TFO PFD. However, the size of osteophytes in the lateral TFO longer correlated with the narrowing of the medial joint gaps TFO and lateral PFD, not his own joint space and osteophytes size in the medial PFD correlated not with a local narrowing of the gap, and a narrowing in the medial TFO. Apparently, the size of osteophytes may affect how changes in related areas of the joint as well as local, that may be mediated by biochemical or mechanical growth factors m. The last most likely can be explained by the size of the connection medial osteophytes TFO and PPO with varus deformity. G.I.van Osch et al (1996) suggested that the processes of cartilage damage and the formation of osteophytes are not directly connected, but are caused by the same factors and develop independently of each other. This independent development is observed in the lateral and medial PFD TFO, the size of osteophytes associated more with lateral patellar subluxation and varus deformity than a local narrowing of the joint space.

The relationship between the total number of osteophytes and their location at several sites support the concept of conditionality of constitutional formation of osteophytes and "hypertrophic" bone response. There may be individual differences in response to the severity of the effect of certain risk factors, such as TGF-beta, or taking part in the growth of osteophytes bone protein-2 (bone morphogenic proteine-2). An interesting observation is the link and the number of osteophytes chondrocalcinosis: Clinical studies suggest the presence of specific relations between the crystals of calcium pyrophosphate (a common cause of chondrocalcinosis) and "hypertrophic" outcome of osteoarthritis. TGF-beta, in addition to stimulating the growth of osteophytes, increases the production of chondrocytes extracellular pyrophosphate, and mechanical stimulation of chondrocytes increases ATP production, a powerful source of extracellular pyrophosphate, thereby predisposing to the formation of crystals of the latter.

Our data suggest involvement in the pathogenesis of osteoarthritis number of factors, including local biomechanical, constitutional and other determining the size and direction of growth of osteophytes, are formed in the course of disease progression.