Ligaments of the knee joint

Conventionally, all stabilizers are divided not into two groups, as was previously accepted, but into three: passive, relatively passive and active. The passive elements of the stabilizing system include bones, the synovial capsule of the joint, the relatively passive ones include menisci, ligaments of the knee joint, fibrous capsule of the joint, and the active ones include muscles with their tendons.

Relatively passive elements involved in stabilizing the knee joint include those that do not actively displace the tibia relative to the femur, but have a direct connection with ligaments and tendons (for example, the menisci), or are themselves ligamentous structures that have a direct or indirect connection with muscles.

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Functional anatomy of the capsular-ligamentous apparatus of the knee

In the joint up to 90°. The PCL acquires the role of a secondary stabilizer for external rotation of the tibia at 90° of flexion, but it plays a lesser role with full extension of the tibia. D. Veltry (1994) also notes that the PCL is a secondary stabilizer with varus deviation of the tibia.

The BCL is the primary stabilizer of valgus deviation of the tibia. It is also the primary limiter of external rotation of the tibia. The role of the BCL as a secondary stabilizer is to limit the anterior displacement of the tibia. Thus, with an intact ACL, transection of the BCL will not change the anterior translation of the tibia. However, after injury to the ACL and transection of the BCL, there is a significant increase in the pathological displacement of the tibia forward. In addition to the BCL, the medial part of the joint capsule also limits the anterior displacement of the tibia to some extent.

The MCL is the primary stabilizer of varus deviation of the tibia and its internal rotation. The posterolateral part of the joint capsule is the secondary stabilizer.

Attachment of the knee joint ligaments

There are two types of attachment: direct and indirect. The direct type is characterized by the fact that most of the collagen fibers penetrate directly into the cortical bone at the point of their attachment. The indirect type is determined by the fact that a significant number of collagen fibers at the entrance continue into the periosteal and fascial structures. This type is characteristic of significant in length sites of attachment to the bone. An example of the direct type is the femoral attachment of the medial collateral ligament of the knee joint, where the transition of the flexible strong ligament to the rigid cortical plate is carried out through four-walled structures, namely: ligaments of the knee joint, unmineralized fibrous cartilage, mineralized fibrous cartilage, cortical bone. An example of different types of attachment within one ligamentous structure is the tibial attachment of the ACL. On the one hand, there is a large widespread indirect attachment, where most of the collagen fibers continue into the periosteum, and on the other hand, there are some fibrocartilaginous junctions with direct entry of collagen fibers into the bone.

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Isometricity

Isometricity is the maintenance of a constant length of the knee joint ligament during articulations. In a hinge joint with a range of motion of 135°, the concept of isometricity is extremely important for a correct understanding of its biomechanics in norm and pathology. In the sagittal plane, movements in the knee joint can be characterized as a connection of four components: two cruciate ligaments and bone bridges between their origins. The most complex arrangement is found in the collateral ligaments, which is associated with the lack of complete isometry during articulations at various flexion angles in the knee joint.

Cruciate ligaments of the knee joint

The cruciate ligaments of the knee joint are supplied with blood from the median artery. General innervation is provided by the popliteal plexus nerves.

The anterior cruciate ligaments of the knee joint are a connective tissue band (on average 32 mm long, 9 mm wide) that runs from the posterior medial surface of the lateral condyle of the femur to the posterior intercondylar fossa on the tibia. A normal ACL has an inclination angle of 27° at 90° of flexion, the rotational component of the fibers at the attachment sites on the tibia and femur is 110°, the angle of intrafascicular twisting of the collagen fibers varies within the range of 23-25°. At full extension, the ACL fibers run approximately parallel to the sagittal plane. There is a slight rotation of the ligament of the knee joint in relation to the longitudinal axis, the shape of the tibial origin is oval, longer in the anteroposterior direction than in the medial-lateral direction.

The posterior cruciate ligament of the knee joint is shorter, stronger (average length 30 mm) and originates from the medial femoral condyle, the shape of the origin is semicircular. It is longer in the anteroposterior direction in its proximal part and has the appearance of a curved arc in the distal part on the femur. The high femoral attachment gives the ligament an almost vertical course. The distal attachment of the PCL is located directly on the posterior surface of the proximal end of the tibia.

The ACL is divided into a narrow, anteromedial bundle, which is stretched during flexion, and a wide posterolateral bundle, which has fiber tension during extension. The VZKL is divided into a wide anterolateral bundle, which is stretched during flexion of the leg, a narrow posteromedial bundle, which experiences tension during extension, and a meniscofemoral band of various shapes, which is tense during flexion.

However, this is rather a conditional division of the bundles of the cruciate ligaments of the knee joint in relation to their tension during flexion-extension, since it is clear that due to their close functional relationship, there are no absolutely isometric fibers. Particularly noteworthy are the works of a number of authors on the sectional-transverse anatomy of the cruciate ligaments, which showed that the cross-sectional area of the PCL is 1.5 times greater than that of the ICL (statistically reliable data were obtained in the area of the femoral attachment and in the middle of the ligament of the knee joint). The cross-sectional area does not change during movements. The cross-sectional area of the PCL increases from the tibia to the femur, and the ICL, on the contrary, from the femur to the tibia. The meniscofemoral ligaments of the knee joint make up 20% by volume of the posterior cruciate ligament of the knee joint. The PCL is subdivided into anterolateral, posteromedial, meniscofemoral parts. We are impressed by the conclusions of these authors, as they are in line with our understanding of this problem, namely:

1. Reconstructive surgery does not restore the three-component complex of the PCL.
2. The anterolateral bundle of the PCL is twice as large as the posteromedial one and plays an important role in the kinematics of the knee joint.
3. The meniscofemoral portion is always present, has similar cross-sectional dimensions to the posteromedial bundle. Its position, size and strength play a significant role in controlling the posterior and posterolateral displacement of the tibia relative to the femur.

Further analysis of the functional anatomy of the knee joint is more appropriate to perform by identifying the anatomical region, since there is a close functional relationship between the passive (capsule, bones) relatively passive (menisci, ligaments of the knee joint) and active components of stability (muscles).

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Medial capsular-ligamentary complex

In practical terms, it is convenient to divide the anatomical structures of this section into three layers: deep, middle and superficial.

The deepest third layer includes the medial capsule of the joint, thin in the anterior section. It is not long, it is located under the medial meniscus, providing its stronger attachment to the tibia than to the femur. The middle part of the deep layer is represented by the deep leaf of the medial collateral ligament of the knee joint. This segment is divided into the meniscofemoral and meniscotibial parts. In the posteromedial section, the middle layer (II) merges with the deeper one (III). This area is called the posterior oblique ligament.

In this case, the close fusion of passive elements with relatively passive ones is clearly visible, which speaks to the conventionality of such a division, although it contains a very specific biomechanical meaning.

The meniscofemoral parts of the ligament of the knee joint further back become thinner and have the least tension during flexion in the joint. This area is strengthened by the tendon m. semimembranosus. Some of the fibers of the tendon are woven into the oblique popliteal ligament, which passes transversely from the distal part of the medial surface of the tibia to the proximal part of the lateral condyle of the femur in a straight direction to the posterior part of the joint capsule. The tendon m. semimembranosus also gives fibers anteriorly to the posterior oblique ligament and to the medial meniscus. The third portion of m. semimembranosus is attached directly to the posteromedial surface of the tibia. In these areas, the capsule is noticeably thickened. The other two heads of m. The semimembranous ligaments attach to the medial surface of the tibia, passing deep (relative to the MCL) to the layer that is connected to the m popliteus. The strongest part of layer III is the deep leaflet of the MCL, which has fibers oriented parallel to the fibers of the ACL at full extension. At maximum flexion, the insertion of the MCL is pulled anteriorly, causing the ligament to run nearly vertically (i.e., perpendicular to the tibial plateau). The ventral insertion of the deep portion of the MCL lies distal and slightly posterior to the superficial layer of the MCL. The superficial leaflet of the MCL runs longitudinally in the intermediate layer. It remains perpendicular to the surface of the tibial plateau during flexion, but is displaced posteriorly as the femur shifts.

Thus, a clear interconnection and interdependence of the activity of various bundles of the knee ligament is visible. Thus, in the flexion position, the anterior fibers of the knee ligament are tense, while the posterior fibers are relaxed. This led us to the conclusion that in conservative treatment of ruptures of the knee ligament, depending on the localization of the damage to the knee ligament, it is necessary to select the optimal flexion angle in the knee joint to maximize the reduction of diastasis between the torn fibers. In surgical treatment, suturing of the knee ligament in the acute period should also be performed, if possible, taking into account these biomechanical features of the knee ligament.

The posterior portions of the II and III layers of the joint capsule are connected in the posterior oblique ligament. The femoral origin of this ligament of the knee joint lies on the medial surface of the femur behind the origin of the superficial leaflet of the BCL. The fibers of the ligament of the knee joint are directed backward and downward and are attached in the area of the posteromedial angle of the articular end of the tibia. The menisco-tibial part of this ligament of the knee joint is very important in the attachment of the posterior part of the meniscus. This same area is an important attachment of m. semimembranosus.

There is no consensus yet on whether the posterior oblique ligament is a separate ligament or is the posterior portion of the superficial layer of the BCL. In case of ACL injury, this area of the knee joint is a secondary stabilizer.

The medial collateral ligament complex limits excessive valgus deviation and external rotation of the tibia. The main active stabilizer in this area are the tendons of the muscles of the large "goose foot" (pes anserinus), which cover the MCL during full extension of the tibia. The MCL (deep portion) together with the ACL also limits the anterior displacement of the tibia. The posterior part of the MCL, the posterior oblique ligament, strengthens the posteromedial part of the joint.

The most superficial layer I consists of a continuation of the deep fascia of the thigh and the tendinous extension of m. sartorius. In the anterior part of the superficial part of the BCL, the fibers of layers I and II become inseparable. Dorsally, where layers II and III are inseparable, the tendons of m. gracilis and m. scmitendinosus lie over the joint, between layers I and II. In the posterior part, the joint capsule is thinned and consists of one layer, with the exception of hidden discrete thickenings.

Lateral capsular-ligamentary complex

The lateral part of the joint also consists of three layers of ligamentous structures. The joint capsule is divided into the anterior, middle, posterior parts, as well as the meniscofemoral and meniscotibial parts. In the lateral part of the joint there is an intracapsular tendon m. popliteus, which goes to the peripheral attachment of the lateral meniscus and is attached to the lateral part of the joint capsule, in front of m. popliteus contains a. geniculare inferior. There are several thickenings of the deepest layer (III). The MCL is a dense strand of longitudinal collagen fibers, lying freely between two layers. This ligament of the knee joint is located between the fibula and the lateral condyle of the femur. The femoral origin of the MCL lies on the ligament connecting the entrance of the tendon m. popliteus (distal end) and the beginning of the lateral head of m. gastrocnemius (proximal end). A little posteriorly and most deeply is lg. arcuatum, which originates from the head of the fibula, enters the posterior capsule near lg. obliquus popliteus. The tendon m. popliteus functions like a ligament. M. popliteus produces internal rotation of the tibia with increasing flexion of the leg. That is, it is more of a rotator of the leg than a flexor or extensor. The MCL is a limiter of pathological varus deviation, despite the fact that it relaxes with flexion.

The superficial layer (I) on the lateral side is a continuation of the deep fascia of the thigh, which surrounds the iliotibial tractus anterolaterally and the biceps femoris tendon posterolaterally. The intermediate layer (II) is the patellar tendon, which originates from the iliotibial tract and the joint capsule, passes medially and attaches to the patella. The iliotibial tract assists the MCL in lateral stabilization of the joint. There is a close anatomical and functional relationship between the iliotibial tract and the intermuscular septum when approaching the insertion site at Gerdy's tubercle. Muller V. (1982) designated this as the anterolateral tibiofemoral ligament, which plays the role of a secondary stabilizer, limiting the anterior displacement of the tibia.

There are also four more ligamentous structures: lateral and medial meniscopatellar ligaments of the knee joint, lateral and medial patellofemoral ligaments of the knee joint. However, in our opinion, this division is very conditional, since these elements are part of other anatomical and functional structures.

A number of authors distinguish a part of the tendon m. popliteus as a ligamentous structure lg. popliteo-fibulare, since this ligament of the knee joint along with lg. arcuaium, MCL, m. popliteus. supports the PCL in controlling the posterior displacement of the tibia. Various articulating structures, for example, the fat pad, the proximal tibiofibular joint, we do not consider here, since they are not directly related to the stabilization of the joint, although their role as certain passive stabilizing elements is not excluded.

Biomechanical aspects of the development of chronic posttraumatic knee instability

Non-contact methods of measuring joint movements during biomechanical testing were used by J. Perry D. Moynes, D. Antonelli (1984).

Electromagnetic devices for the same purposes were used by J. Sidles et al. (1988). Mathematical modeling for processing information about movement in the knee joint was proposed.

Joint movements can be thought of as various combinations of translations and rotations controlled by several mechanisms. There are four components that influence joint stability, helping to keep the articulating surfaces in contact with each other: passive soft tissue structures, such as the cruciate and collateral ligaments of the knee joint, the menisci, which act either directly by tensioning the corresponding tissues, limiting movements in the tibiofemoral joint or indirectly by creating a compressive load on the joint; active muscle forces (active-dynamic components of stabilization), such as traction of the quadriceps femoris, hamstring muscles, the mechanism of action of which is associated with limiting the amplitude of movements in the joint and transforming one movement into another; external influence on the joint, such as moments of inertia arising during locomotion; geometry of the articulating surfaces (absolutely passive elements of stability), limiting movements in the joint due to the congruence of the articulating articular surfaces of the bones. There are three translational degrees of freedom of motion between the tibia and femur, described as anteroposterior, medial-lateral, and proximal-distal; and three rotational degrees of freedom of motion, namely flexion-extension, valgus-varus, and external-internal rotation. In addition, there is the so-called automatic rotation, which is determined by the shape of the articulating surfaces in the knee joint. Thus, when the leg is extended, its external rotation occurs, its amplitude is small and averages 1°.

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The stabilizing role of the knee joint ligaments

A number of experimental studies have allowed us to study the ligament function in more detail. The selective sectioning method was used. This allowed us to formulate the concept of primary and secondary stabilizers in the norm and with damage to the ligaments of the knee joint. We published a similar proposal in 1987. The essence of the concept is as follows. The ligamentous structure that provides the greatest resistance to anteroposterior dislocation (translation) and rotation occurring under the influence of an external force is considered a primary stabilizer. Elements that provide a smaller contribution to resistance under an external load are secondary limiters (stabilizers). Isolated intersection of primary stabilizers leads to a significant increase in translation and rotation, which this structure limits. When crossing secondary stabilizers, no increase in pathological displacement is observed with the integrity of the primary stabilizer. With sectional damage to the secondary and rupture of the primary stabilizer, a more significant increase in pathological displacement of the tibia relative to the femur occurs. The knee ligament can act as a primary stabilizer of certain translations and rotations while also secondarily limiting other joint movements. For example, the BCL is a primary stabilizer for valgus deviation of the tibia, but also acts as a secondary limiter for anterior displacement of the tibia relative to the femur.

The anterior cruciate ligament of the knee joint is the primary limiter of anterior displacement of the tibia at all angles of flexion in the knee joint, taking on about 80-85% of the resistance to this movement. The maximum value of this limitation is observed at 30 ° flexion in the joint. Isolated sectioning of the ACL leads to greater translation at 30 ° than at 90 °. The ACL also provides a primary limitation of medial displacement of the tibia at full extension and 30 ° flexion in the joint. A secondary role of the ACL as a stabilizer is to limit rotation of the tibia, especially at full extension, and is a greater restraint of internal rotation than external rotation. However, some authors point out that with isolated damage to the ACL, minor rotational instability occurs.

In our opinion, this is due to the fact that both the ACL and the PCL are elements of the central axis of the joint. The magnitude of the leverage force for the ACL on the rotation of the tibia is extremely small, and is practically absent for the PCL. Therefore, the effect on the limitation of rotational movements from the cruciate ligaments is minimal. Isolated intersection of the ACL and posterolateral structures (tendons m. popliteus, MCL, lg. popliteo-fibulare) leads to an increase in the anterior and posterior displacement of the tibia, varus deviation and internal rotation.

Active-dynamic stabilization components

In studies devoted to this issue, more attention is paid to the effect of muscles on passive ligamentous elements of stabilization by means of tension or relaxation at certain angles of flexion in the joint. Thus, the quadriceps muscle of the thigh has the greatest effect on the cruciate ligaments of the knee joint when the shin is flexed from 10 to 70°. Activation of the quadriceps muscle of the thigh leads to an increase in the tension of the ACL. On the contrary, the tension of the PCL decreases. The muscles of the posterior group of the thigh (hamstring) somewhat reduce the tension of the ACL when flexed more than 70°.

To ensure consistency in the presentation of the material, we will briefly repeat some of the data that we discussed in detail in previous sections.

The stabilizing function of the capsular-ligamentous structures and periarticular muscles will be discussed in more detail a little later.

What mechanisms ensure the stability of such a complexly organized system in statics and dynamics?

At first glance, the forces at work here are counterbalancing each other in the frontal plane (valgus-varus) and sagittal (anterior and posterior displacement). In reality, the knee joint stabilization program is much deeper and is based on the concept of torsion, i.e. the mechanism of its stabilization is based on a spiral model. Thus, the internal rotation of the tibia is accompanied by its valgus deviation. The outer articular surface moves more than the inner one. Starting the movement, the condyles slide in the direction of the rotation axis in the first degrees of flexion. In the flexion position with valgus deviation and external rotation of the tibia, the knee joint is much less stable than in the flexion position with varus deviation and internal rotation.

To understand this, let us consider the shape of the articular surfaces and the conditions of mechanical loading in three planes.

The shapes of the articular surfaces of the femur and tibia are discongruent, that is, the convexity of the former is greater than the concavity of the latter. The menisci make them congruent. As a result, there are actually two joints - meniscofemoral and mesicotibial. During flexion and extension in the meniscofemoral section of the knee joint, the upper surface of the menisci comes into contact with the posterior and lower surfaces of the femoral condyles. Their configuration is such that the posterior surface forms an arc of 120° with a radius of 5 cm, and the lower surface - 40° with a radius of 9 cm, that is, there are two centers of rotation and during flexion one replaces the other. In reality, the condyles twist in the form of a spiral and the radius of curvature constantly increases in the posteroanterior direction, and the previously named centers of rotation correspond only to the end points of the curve along which the center of rotation moves during flexion and extension. The lateral ligaments of the knee joint originate in places corresponding to the centers of its rotation. As the knee joint extends, the ligaments of the knee joint are stretched.

In the menisco-femoral section of the knee joint, flexion and extension occur, and in the menisco-tibial section formed by the lower surfaces of the menisci and the articular surfaces of the tibia, rotational movements around the longitudinal axis occur. The latter are possible only when the joint is bent.

During flexion and extension, the menisci also move in the anteroposterior direction along the articular surfaces of the tibia: during flexion, the menisci move backwards together with the femur, and during extension, they move back, i.e. the menisco-tibial joint is mobile. The movement of the menisci in the anteroposterior direction is caused by the pressure of the condyles of the femur and is passive. However, traction on the tendons of the semimembranosus and popliteal muscles causes some of their displacement backwards.

Thus, it can be concluded that the articular surfaces of the knee joint are incongruent, they are strengthened by capsular-ligamentous elements, which, when loaded, are subject to forces directed in three mutually perpendicular planes.

The central pivot of the knee joint, which ensures its stability, is the cruciate ligaments of the knee joint, which complement each other.

The anterior cruciate ligament originates on the medial surface of the lateral condyle of the femur and ends in the anterior part of the intercondylar eminence. It has three bundles: posterolateral, anterolateral, and intermediate. At 30° flexion, the anterior fibers are more tense than the posterior fibers, at 90° they are equally tense, and at 120' the posterior and lateral fibers are more tense than the anterior fibers. At full extension with external or internal rotation of the tibia, all fibers are also tense. At 30° with internal rotation of the tibia, the anterolateral fibers are tense, and the posterolateral fibers are relaxed. The axis of rotation of the anterior cruciate ligament of the knee joint is located in the posterolateral part.

The posterior cruciate ligament originates on the outer surface of the medial condyle of the femur and ends in the posterior part of the intercondylar eminence of the tibia. It has four bundles: the anteromedial, posterolateral, meniscofemoral (Wrisbcrg) and the strongly forward, or Humphrey ligament. In the frontal plane, it is oriented at an angle of 52-59 °; in the sagittal - 44-59 °. Such variability is due to the fact that it performs a dual role: during flexion, the anterior fibers are stretched, and during extension, the posterior fibers. In addition, the posterior fibers participate in passive counteraction of rotation in the horizontal plane.

In valgus deviation and external rotation of the tibia, the anterior cruciate ligament limits the anterior displacement of the medial part of the tibial plateau, and the posterior cruciate ligament limits the posterior displacement of its lateral part. In valgus deviation and internal rotation of the tibia, the posterior cruciate ligament limits the posterior displacement of the medial part of the tibial plateau, and the anterior cruciate ligament limits the anterior dislocation of the medial part.

When the flexor and extensor muscles of the lower leg are strained, the tension of the anterior cruciate ligament of the knee joint changes. Thus, according to P. Renstrom and SW Arms (1986), with passive flexion from 0 to 75°, the tension of the ligament of the knee joint does not change, with isometric tension of the ischiocrural muscles, the anterior displacement of the tibia decreases (the maximum effect is between 30 and 60°), isometric and dynamic tension of the quadriceps muscle is accompanied by tension of the ligament of the knee joint usually from 0 to 30° of flexion, simultaneous tension of the flexors and extensors of the lower leg does not increase its tension at a flexion angle of less than 45°.

On the periphery, the knee joint is limited by the capsule with its thickenings and ligaments, which are passive stabilizers that counteract excessive displacement of the tibia in the anteroposterior direction, its excessive deviation and rotation in various positions.

The medial lateral or tibial collateral ligament consists of two bundles: one is superficial, located between the tubercle of the femoral condyle and the inner surface of the tibia, and the other is deep, wider, running in front and behind the superficial fascia. The posterior and oblique deep fibers of this ligament of the knee joint are stretched during flexion from an angle of 90° to full extension. The tibial collateral ligament keeps the shin from excessive valgus deviation and external rotation.

Behind the tibial collateral ligament of the knee joint there is a concentration of fibers called the postero-internal fibro-tendinous nucleus (noyau fibro-tendineux-postero-interne) or postero-internal angular point (point d'angle postero-inteme).

The lateral collateral ligament or fibular collateral ligament is classified as extra-articular. It originates from the tubercle of the lateral condyle of the femur and attaches to the head of the fibula. The function of this ligament of the knee joint is to keep the shin from excessive varus deviation and internal rotation.

At the back is the fabellofibular ligament, which originates from the fabella and attaches to the head of the fibula.

Between these two ligaments is located the postero-external fibro-tendinous nucleus (noyau fibro-tendmeux-postero-externe) or postero-internal angular point (point d'angle postero-externe), formed by the attachment of the tendon of the popliteal muscle and the most external fibers of the thickenings of the capsule (the external arch of the popliteal arch or ligaments of the knee joint).

The posterior ligament plays an important role in limiting passive extension. It consists of three parts: the middle and two lateral ones. The middle part is connected with the extension of the oblique popliteal ligament of the knee joint and the terminal fibers of the semimembranosus muscle. Passing to the popliteal muscle, the arch of the popliteal ligament of the knee joint with its two bundles complements the posterior median structures. This arch strengthens the capsule only in 13% of cases (according to Leebacher), and the fabellofibular ligament - in 20%. There is an inverse relationship between the importance of these inconstant ligaments.

The alar ligaments of the knee joint, or patellar retinacula, are formed by a multitude of capsular-ligamentous structures - the femoropatellar, oblique and crossing fibers of the external and internal vastus femoris, oblique fibers of the broad fascia of the thigh and the aponeurosis of the sartorius muscle. The variability of the direction of the fibers and the intimate connection with the surrounding muscles, which can stretch them when contracted, explain the ability of these structures to perform the function of active and passive stabilizers, similar to the cruciate and collateral ligaments.

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Anatomical basis of rotational stability of the knee

The fibro-tendinous periarticular nuclei (les noyaux fibro-tendineux peri-articulaires) between the thickening zones of the joint capsule are represented by ligaments, among which four fibro-tendinous nuclei are distinguished, in other words, different sections of the capsule and active muscular-tendinous elements are distinguished. The four fibro-tendinous nuclei are divided into two anterior and two posterior.

The anterior medial fibro-tendinous nucleus is located in front of the tibial collateral ligament of the knee joint and includes the fibers of its deep bundle, the femoropatellar and medial meniscopatellar ligaments; the tendon of the sartorius muscle, the gracilis muscle, the oblique part of the tendon of the semimembranosus muscle, the oblique and vertical fibers of the tendinous part of the vastus femoris.

The posteromedial fibrotendinous nucleus is located behind the superficial bundle of the tibial collateral ligament of the knee joint. In this space, the deep bundle of the mentioned ligament of the knee joint, the oblique bundle coming from the condyle, the attachment of the internal head of the gastrocnemius muscle and the direct and recurrent bundle of the tendon of the semimembranosus muscle are distinguished.

The anterolateral fibrotendinous nucleus is located in front of the fibular collateral ligament and includes the joint capsule, the femoropatellar and lateral meniscopatellar ligaments of the knee joint, and the oblique and vertical fibers of the tensor fascia lata muscle.

The posterolateral fibrotendinous nucleus is located behind the peroneal collateral ligament of the knee joint. It consists of the popliteal tendon, the fabelloperoneal tendon, the most superficial fibers coming from the condyle with fibers of the outer part (arch) of the popliteal arch (ligament of the knee joint), the attachment of the lateral head of the gastrocnemius muscle and the tendon of the biceps femoris.

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