Ultrasound signs of diseases and injuries of the knee joint

The anatomical structure and functional loads in the knee joint create a high probability of its overload and injury, development of various diseases. Even minor dysfunctions of this joint lead to significant discomfort for a person, loss of ability to work, and in case of significant damage, to disability. All pathological changes in the knee joint can be divided into several main groups.

1. Injuries to the tendon-ligament apparatus:
   • quadriceps tendon injuries;
   • damage to the patellar ligament;
   • damage to the medial collateral ligament;
   • damage to the lateral collateral ligament;
   • anterior cruciate ligament injuries;
   • posterior cruciate ligament injuries.
2. Pathological changes in the menisci:
   • degenerative changes;
   • breaks;
   • operated meniscus;
   • cysts;
   • dysplasia.
3. Pathological changes in the synovial membrane:
   • synovial fold hyperplasia;
   • vilonodular synovitis;
   • osteochondromatosis;
   • synovial sarcoma;
   • rheumatic synovitis.

Quadriceps tendon ruptures

Damage to the quadriceps tendon occurs due to compression or excessive contraction of the muscle. Partial and complete ruptures are distinguished. Most often, ruptures are localized in the transition zone of the tendon part to the muscle or in the place where the quadriceps tendon transitions to the patellar ligament, less often in the place where the tendon attaches to the bone. Ruptures are caused by injuries, degenerative processes or systemic diseases such as diabetes mellitus, rheumatoid arthritis, erythematoses, hyperparathyroiditis. Clinically, at the time of rupture, the patient feels a crack, which is sometimes heard at a distance. The function of the quadriceps muscle is lost with complete ruptures, with partial ruptures in the acute period, knee extension is impossible. With partial ruptures, patients complain of pain, swelling of the knee and limitation of knee extension.

In ultrasound examination, a complete rupture of the quadriceps tendon under sensor compression looks like a complete disruption of the integrity of the fibers and fibrillar structure of the tendon. The defect is replaced by a hematoma, and effusion appears in the anterior fold. When a tendon rupture is accompanied by a rupture of the joint capsule, hemarthrosis occurs. In the case of a partial rupture, there is a local disruption of the integrity of the fibers and fibrillar structure with the appearance of hypoechoic areas in their place. The contours of the tendon usually do not change, and the tendon itself is not thickened.

In case of intra-trunk - partial ruptures, the contours of the tendon are preserved, but at the site of the rupture a hypoechoic area is visualized, where there is a break in the fibrillar structure of the tendon. In MRI on T2-weighted images in the projection of the fibers of the quadriceps muscle of the thigh, a high-intensity signal is visualized. After the course of treatment, the fibers of the tendons and ligaments do not regenerate completely and do not restore their original structure. In case of recurrent partial ruptures, despite the preserved contours of the tendon, at the site of injury there is a replacement of fibrillar fibers with connective tissue. Scar tissue is formed at the site of the rupture, which on ultrasound looks like a hyperechoic zone of fibrosis.

Patella fracture

In sports injuries, ruptures of the quadriceps and its tendon are very common, sometimes in combination with a fracture of the patella. The mechanism of this injury is a forced contraction of the quadriceps, for example, in weightlifters or football players.

The most common fractures of the patella are transverse, less common are comminuted, segmental, stellate, vertical and others. Divergence of fragments always indicates ruptures of the lateral ligaments of the knee joint. If the lateral ligaments are intact, there is no divergence of fragments. Hemarthrosis of varying degrees is always observed, spreading to the upper recess. During ultrasound examination, a fracture of the patella looks like a violation of the integrity of the contours of the patella with varying degrees of divergence of the edges of the fragments, depending on the type of fracture and the accompanying rupture of the lateral ligaments.

Ruptures of the patellar ligament

Ruptures of the patellar ligament itself occur as a result of direct trauma, such as a fall on a bent knee. The rupture is localized under the patella, often closer to the tibial tuberosity. Ligament damage is combined with effusion in the area of the infrapatellar bursa. The kneecap, due to the contraction of the quadriceps muscle, is displaced upward. With a complete rupture, the fibrillar structure of the ligament disappears, and a hematoma and effusion in the infrapatellar bursa appear in its place. With a partial rupture, the fibrillar structure of the ligament is partially preserved. Also, ligament ruptures easily occur against the background of chronic tendinitis.

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Suprapatellar bursitis

The suprapatellar bursa is the largest bursa. It extends 6 cm upward from the proximal part of the patella and is called the superior recess. From the 5th month of intrauterine development, holes may appear in the wall of the bursa, through which communication is established between the bursa and the cavity of the knee joint. This phenomenon occurs in 85% of adults. Any changes inside the knee joint are reflected in the form of effusion in the suprapatellar bursa.

On ultrasound, suprapatellar bursitis often appears as a triangular area of decreased echogenicity. Depending on the contents, the echogenicity of the bursa may be increased or decreased.

Semimembranous, tibial collateral bursitis

Semimembranosus tibial collateral bursitis is a fluid-filled, U-shaped bursa that covers the semimembranosus tendon on the medial and anterior side. Inflammation of the bursa causes local pain at the level of the medial joint line and clinically resembles a meniscal tear.

Bursitis of the internal collateral ligament

The bursa of the medial collateral ligament is located between the medial meniscus and the medial collateral ligament. Effusion occurs due to inflammation, meniscocapsular separation, or damage to the medial collateral ligament. Inflammation of the bursa causes local pain along the medial surface of the joint, clinically resembling a tear of the medial meniscus.

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Joint effusion

Knee joint injuries are often accompanied by bleeding into the joint. Hemorrhagic effusion that forms two hours after the injury may indicate a rupture of the lateral or cruciate ligaments, meniscus, patellar dislocation, or intra-articular fracture of the femoral condyles. The amount of blood in hemarthrosis of the knee joint varies. Blood in the joint cavity stimulates the production of synovial fluid, leading to even greater stretching of the bursa and capsule of the joint. The more fluid in the joint, the more severe the pain.

For better visualization of fluid in the joint, functional tests are performed in the form of tension of the quadriceps muscle of the thigh or compression of the lateral synovial fold. Fluid in the joint cavity is better determined with medial and lateral access.

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Tendinitis

The most common tendinitis is of the quadriceps tendon, patella, and biceps tendon. With tendinitis, the tendon thickens, its echogenicity decreases. The anisotropy effect characteristic of the tendon disappears. Increased vascularization is observed along the tendon fibers.

Tendinitis of the quadriceps tendon. Patients complain of local pain and swelling in the area of the ligament or tendon. Depending on the location, the symptoms are similar to those of meniscus and patella disease. With tendinitis, the quadriceps tendon thickens at the point of attachment to the patella, and its echogenicity decreases. With chronic tendinitis, micro-tears, fibrous inclusions in the tendon fibers, and calcification areas may occur. These changes are united under the general name of degenerative changes in the tendon.

Tendinitis of the patellar ligament. The most common type of tendinitis is the tendinitis of the patellar ligament. It can be: local (in the area of attachment to the patella or tibia) or diffuse. Local tendinitis is often found in jumpers, long-distance runners, volleyball and basketball players with constant loads. It is called "jumper's knee" and "inverted jumper's knee". Tendinitis mainly affects the deep parts of the ligament at the attachment site. However, any part of the ligament can be involved in the pathological process. In this case, the ligament thickens either in the area of its attachment to the patella or in the area of attachment to the tibia. In chronic tendinitis, calcifications and fibrosis areas appear at the attachment site of the ligament to the bone.

In a chronic process, the presence of dystrophic calcification in the damaged segment is observed. The Hoffa fat pad can increase due to infringement and inflammation. In ultrasound, hypertrophy of the Hoffa fat pad, as a consequence of mucoid degeneration, is determined as a hyperechoic structure.

Iliotibial band friction syndrome

Iliotibial band friction syndrome, or "runner's knee," is more of a fasciitis than a tendinitis. It occurs when the iliotibial band repeatedly rubs against a deformed lateral femoral epicondyle, causing inflammation of the fascia that forms the iliotibial band. It is most common in runners, especially sprinters who run with their legs raised high.

Ultrasound examination should be performed immediately after physical activity causing pain. On ultrasound, an enlarged fascia of decreased echogenicity will be visible over the lateral femoral condyle.

Osgood-Schlatter disease

This is a type of chondropathy affecting the patellar ligament and the tuberosity of the tibia. It occurs as a result of repeated microtraumas to this area. With this disease, the patient experiences spontaneous pain in the knee, which increases when bending the knee joint.

The ultrasound signs are the same as with ligament inflammation, but with this pathology there are bone inclusions in the ligament.

The distal part of the patellar ligament thickens and hypoechoic areas with fragments of the anterior tuberosity of the tibia are identified in it.

Rupture of the medial collateral ligament

Damage to the medial collateral ligament is the most common. The mechanism of its injury: with a bent knee and a fixed foot, there is a sharp external rotation of the shin with inward rotation of the femur. Clinically, pain and swelling occur in the area of damage.

A symptom of lateral swing of the lower leg is observed when pressure is applied to the outer surface of the knee joint while simultaneously abducting the lower leg. Damage to the medial collateral ligament significantly increases the valgus position of the knee. Damage can occur anywhere along the ligament: in the proximal part, in the area of its attachment to the medial condyle of the femur; in the distal part, where the ligament attaches to the condyle of the tibia, and at the attachment to the medial meniscus - above the joint line. If the rupture occurs at the level of the joint line, where the medial ligament is fused with the meniscus, then such an injury can be combined with simultaneous damage to the medial meniscus and the anterior cruciate ligament. Ruptures of the medial collateral ligament are possible at various levels due to the complexity of the structure of its fibers. A distinction is made between partial and complete rupture of the lateral ligaments of the knee joint. There may be ruptures of only superficial fibers, or superficial and deep, as well as ruptures with a bone fragment being torn off. A complete rupture of one of the lateral ligaments leads to instability in the knee joint. Ultrasound examination reveals: disruption of the integrity of the ligament fibers, displacement of fibers under functional load, a hypoechoic area (hematoma), and decreased echogenicity due to soft tissue edema.

Rupture of the lateral collateral ligament

The lateral collateral ligament is damaged less frequently than the internal one. Its ruptures are caused by strong internal rotation of the tibia. Sometimes, instead of a ligament rupture, a bone fragment of the head of the fibula with the lateral ligament attached here is torn off. The adjacent peroneal nerve is often damaged. Ultrasound signs are the same as with a rupture of the internal collateral ligament: disruption of the integrity of the ligament fibers, displacement of fibers under functional load, formation of a hypoechoic area (hematoma), decreased echogenicity due to swelling of soft tissues and subcutaneous fat.

Dystrophic calcification of the lateral collateral ligament occurs predominantly in athletes, particularly long-distance runners.

Pellegrini-Stieda calcification

The syndrome is a post-traumatic ossification of paraarticular tissues occurring in the area of the medial femoral condyle. The disease is usually observed in young men who have suffered a traumatic injury to the knee joint. The injury may be mild or severe, direct or indirect. After the acute symptoms of the injury disappear, a period of improvement may occur, but complete restoration of the knee joint does not occur. Extension in the knee joint remains limited. On ultrasound, multiple ossifications are determined in the structure of the medial collateral ligament in the form of a soft hyperechoic focus, located mainly in the area of attachment of the ligament to the epicondyle of the femur.

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Anterior Cruciate Ligament Injuries

Anterior cruciate ligament injury is the most common. The mechanism of injury is overexertion in rotation, falling with a fixed foot, and excessive hyperextension of the knee joint. Tears are more common in combination with other injuries: for example, with a tear of the medial collateral ligament and medial meniscus.

The main symptoms of injury are a feeling of instability in the joint, swelling and pain when moving in the primary post-traumatic period. The most valuable clinical symptom of rupture of the anterior cruciate ligament is the "anterior drawer" symptom. To do this, the patient needs to bend the knee to a right angle, while the shin can be easily pushed forward in relation to the thigh. Most often, the ligament is damaged in the proximal and less often in the central sections. It is very important to detect a ligament rupture in time, as this will determine the nature of the operation.

MRI is a more accurate and reliable method for diagnosing anterior cruciate ligament injuries. In MRI tomograms, in case of a recent injury, an increase in signal intensity is noted in the rupture zone, which normally has moderate intensity on T1- and is more intense on T2-weighted images. Damaged fibers of the anterior cruciate ligament are not clearly differentiated or are not determined at all. MRI diagnostics of a partial rupture in case of a recent injury can be complicated by local edema and discontinuity of the fiber course. There are indirect signs for diagnosing anterior cruciate ligament rupture: its displacement below 45° in relation to the tibial plateau, local change in its trajectory and posterior displacement of the lateral meniscus by more than 3.5 mm in relation to the tibial plateau. In old ruptures, thinning of the ligament is noted without edema of the synovial membrane.

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Posterior Cruciate Ligament Tear

Rupture of the posterior cruciate ligament is quite rare. The main mechanism of rupture is hyperflexion during a jump. Most often, the rupture is localized in the body of the ligament itself or at the level of its attachment to the tibia.

Meniscus injuries

Meniscus tears are considered the most common type of knee injury. Meniscus injuries can occur at any age. With age, the meniscus becomes weak and fragile. Any incorrect and sudden movement can provoke their rupture. The medial meniscus is damaged 10 times more often than the lateral one. This is due to the anatomical and morpho-functional features of the medial meniscus. The mechanism of isolated injury is a fall from a height onto legs straightened at the knee joint, with a sharp and deep bending in the knee joints at the moment of squatting and an attempt to straighten up. However, more often the meniscus is damaged with a sharp rotational movement in the knee joint - rotation of the thigh inward with a fixed shin and foot. A predisposing factor is undoubtedly previous microtrauma. The main clinical symptom of meniscus damage is a "blockade" of the knee joint. The part of the meniscus torn off during injury may shift and take an incorrect position in the joint, becoming trapped between the articular surfaces of the tibia and femur. The trap blocks the joint in a forced flexed position. A tear and trapping of the anterior horn of the medial meniscus block the knee joint so that the final 30° of extension are impossible. Trapping due to a "watering can handle" tear limits the last 10-15° of extension. Joint block due to strangulation of a torn meniscus does not limit knee flexion. A torn posterior horn very rarely blocks the joint. Joint block is usually temporary. Unblocking restores all movements in the joint.

During an ultrasound examination of a meniscus rupture, effusion is usually observed in the area of the damaged meniscus. The meniscus takes on an irregular shape with a hypoechoic stripe at the site of the rupture. It should be noted that normally the meniscus may have a hypoechoic stripe in the middle part of the meniscus.

The use of tissue harmonic mode improves the visualization of meniscus tears by improving the contrast elaboration of details. Three-dimensional reconstruction has a certain value in determining the extent. It is also worth emphasizing the importance of energy mapping for the diagnosis of meniscus tears. The presence of localized increased vascularization around the affected area helps to suspect and determine the localization of the tear.

The main signs of meniscus damage include:

• violation of the integrity of the meniscus contours;
• fragmentation or presence of hypoechoic areas;
• the appearance of a hypoechoic strip in the structure of the meniscus;
• formation of effusion;
• soft tissue swelling;
• displacement of the lateral ligaments of the knee joint;
• increased degree of vascularization in the area of the meniscus tear.

Some types of meniscus tears can be detected by ultrasound. These include transchondral and paracapsular tears. The most common is the typical, longitudinal meniscus tear, in which the middle portion of the meniscus is torn, while the ends, anterior and posterior, remain intact. This tear is called a "watering can handle" tear. A tear that runs along a radial fiber to the inner free edge is called a "parrot beak" tear. Repeated microtrauma to the meniscus leads to a secondary tear with damage to the anterior, middle, and posterior portions of the meniscus.

Ruptures of the anterior horn and of the "watering can handle" type often occur with recurrent blockades that occur during rotation of the shin, i.e. with the same mechanism by which the rupture occurred. Sometimes the knee "jumps out", according to the patient, for no known reason when walking on a flat surface and even in sleep. Displacement of the torn posterior horn sometimes causes the patient to feel the knee joint "bending".

A meniscus rupture is accompanied by effusion in the knee joint, which appears several hours after the injury. It is caused by concomitant damage to the synovial membrane of the joint. Subsequent relapses of blockade and "bending" attacks also occur with effusion in the joint. The more often blockades and "bendings" occur, the less subsequent transudation in the joint. A condition may occur when after the usual blockade, effusion is no longer detectable. A rupture of the outer meniscus occurs by the same mechanism as the inner one, with the only difference being that the rotational movement of the leg is performed in the opposite direction, i.e. not outward, but inward. Blockade of the joint with a rupture of the outer meniscus occurs rarely, and if it does occur, it is not accompanied by effusion in the joint.

On MRI tomograms, with a true rupture, the signal intensity increases toward the periphery of the meniscus. A true rupture is clearly visible when the axis of the scanning layer is perpendicular to the axis of the lesion. If the rupture is oblique, the resulting artifacts may mask the damage.

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Degenerative changes and meniscus cysts

Degenerative changes in the meniscus are characterized by heterogeneity of their structure, fragmentation, hyperechoic inclusions and cysts. Similar changes are observed in old meniscus injuries. Cysts of the outer meniscus are more common. Cysts cause pain and swelling along the joint line. Cysts of the inner meniscus are larger in size than those of the outer meniscus and are less fixed. A meniscus cyst looks like a rounded structure with smooth, clear internal and external contours, with an anechoic internal structure and the effect of distal amplification of the ultrasound signal. Additional scanning modes (tissue harmonics and adaptive colorization) improve visualization of cyst contours. Over time, the fluid in the cyst becomes heterogeneous, with thick contents. As the size increases, cysts tend to soften.

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Baker's cysts

Baker's cysts are one of the most common pathologies in athletes. As a rule, these cysts are asymptomatic and are an ultrasound or clinical finding. The substrate for the development of this cyst is the stretching of the bursa located between the tendons of the semimembranosus and gastrocnemius muscles. The differential diagnostic sign of Baker's cyst is the visualization of the cyst neck communicating with the cavity of the knee joint in the area of the medial part of the popliteal fossa: between the medial head of the gastrocnemius muscle and the tendon of the semimembranosus muscle. As a manifestation of the inflammatory reaction in the surrounding tissues, there is an increase in vascularization, which is recorded in the energy mapping mode. An increase in fluid in the joint cavity leads to the accumulation of fluid in the bursa and the development of a cyst. Cysts have different sizes and lengths. The contents of the cysts are different: "fresh" cysts have anechoic contents, old ones - heterogeneous. In fresh Baker's cysts, the contents are liquid, while in old forms, they are jelly-like. A Baker's cyst rupture is diagnosed by the presence of a characteristic pointed edge and a strip of fluid along the fibers of the gastrocnemius tendon. Ruptures in the lower part of the cyst are more typical. Panoramic scanning mode allows visualization of the cyst along its entire length.

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Deforming arthrosis

The disease occurs as a result of metabolic disorders in the articular cartilage, mechanical loads due to excess body weight, and physical overload. Regardless of the cause, the clinical manifestations of arthrosis are similar and depend on the phase: exacerbation, subacute phase, or remission. Ultrasound can detect the earliest changes in bone structures that are not detected by X-ray examination. The main ultrasound signs that can be used to establish the presence of deforming arthrosis are: uneven thinning of the hyaline cartilage, uneven contours of the femur and tibia, the presence of marginal osteophytes, narrowing of the joint space, and prolapse of the menisci. The presence of hyperechoic marginal osteophytes with normal joint space sizes and hyaline cartilage thickness characterizes early manifestations of the disease. The progression of the disease is characterized by the formation of marginal osteophytes with an acoustic shadow, narrowing of the joint space and pronounced thinning of the hyaline cartilage. Subsequently, thinning of the hyaline cartilage (less than 1 mm) occurs with the formation of coarse osteophytes and prolapse of the meniscus by a third of its width. At the stage of pronounced changes, complete prolapse of the meniscus, deformation of its intra-articular part, absence of the joint space, coarse massive osteophytes along all edges of the articular surface are observed.

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Pathology of cartilage tissue

Pathological changes in the hyaline cartilage are characterized by a violation of its normal thickness and calcifications. Thinning of the hyaline cartilage is more common in older people. Inflammatory synovitis or septic arthritis also cause a sharp destruction of proteoglycans and thinning of the cartilage. As the pathological process progresses, necrosis zones, cysts and ossifications are formed. Single osteophytes are formed primarily along the edge of the hyaline cartilage in the cortical layer of the bone. Such changes are normal for older people.

Thinning of cartilage is observed in osteoarthritis. Cartilage is destroyed, and new cartilage is formed in the form of osteophytes. Some defects of the cartilaginous tissue surface are replaced by scar tissue, which is close to cartilaginous in its morphological composition. This occurs as a result of local lesions with the formation of so-called fibrous cartilage. Such changes are well defined on MRIs due to the low signal intensity in the affected area. Thickening of cartilage occurs in acromegaly. These are the first signs of the disease. Cartilage can also increase in size in myxedema and some mucopolysaccharidoses, with extensive erosions.

Koenig's disease

The disease occurs at a young age and affects the tibial epiphysis, cartilage, tendon and serous bursa. The lesion is usually unilateral. A section of articular cartilage, together with the adjacent bone, is separated from the articular surface.

The typical site of damage is the medial femoral condyle, less commonly other parts of the articular ends and the patella. In adults, osteochondritis dissecans can sometimes occur after mechanical damage. The rejected free body in the joint can grow and reach quite large sizes.