Anatomy of the leg above and below the knee joint

The lower limb, from an anatomical point of view, is rarely of interest to people who have little knowledge in this area. An ordinary person most often imagines the leg as a single mass of soft tissue that surrounds some large bones. The only area accessible to understanding is the knee - but its study is usually limited to external landmarks. Most people call only the patella of all the structures of this joint.

Therefore, it is necessary to dwell in more detail on the issue of the anatomy of the lower limb - more precisely, its section, which includes the thigh and lower leg. It is important not only to determine their exact boundaries, but also to understand their internal structure. This section of the leg is only externally unremarkable - inside it contains the largest anatomical formations in the body.

And they are all located on the hip, which is the most important supporting structure of the body. This list includes both skeletal elements and soft tissues - the femur, sciatic nerve, great saphenous vein. But these formations are not isolated - on the thigh and lower leg they form a single whole, differing only in size. Therefore, large sections of the lower limb should be considered as an integral structure, only functionally separated by the knee joint.

Hip

This part of the body has the shape of a truncated cone - its apex is the knee, and its base smoothly borders the body. This appearance is due to the structure of the soft tissues - the upper segment of the thigh contains a large number of muscles. In the lower section, the muscles smoothly transform into wide and strong ligaments, as a result of which the volume of the limb decreases.

The thigh, as a part of the body, has clear boundaries, although an ordinary person is unlikely to be able to correctly indicate them. Therefore, we should consider exactly how it is located in relation to the torso and lower leg:

1. The upper border is not transverse along its entire length - in front it runs along the skin inguinal folds, going obliquely downwards. From the side, the leg is delimited from the body along a line drawn through the iliac crest. From behind, the border acquires a transverse direction, passing in the gluteal fold. Its general internal direction corresponds to the plane drawn through the hip joint.
2. The lower border of the thigh does not have such structural features, and is calculated quite simply - in relation to the patella. The upper pole of the patella is determined, after which a perpendicular line is drawn 5 centimeters above it.

Knowing the correct boundaries of any part of the body allows the doctor to accurately assess the localization of pathological processes, and also helps to easily find large vessels or nerves in their projection.

Skeleton

The entire static and functional load in this part of the body is assumed by a single bone – the femur. It is the largest indivisible structure of the musculoskeletal system in all respects - size and weight. According to the anatomical classification, the femur has a tubular structure, which is characteristic of the most loaded and durable formations in the skeleton.

Since it is only one supporting element of the upper segment of the leg, it has to take on the interaction with all the soft tissues. Therefore, the femur has a rather interesting structure:

• The upper part consists of the head and neck, which are part of the hip joint. In relation to the segments lying below, they are located at a slight angle. This device not only provides good support, but also increases the range of motion in the joint.
• Further, the neck passes into a large tuberous formation - the greater and lesser trochanter of the femur. They are the attachment point for the large gluteal muscles.
• Then the largest and longest segment begins - the body of the bone. It has a characteristic tubular structure, expanding slightly in the lower section. On its posterior surface there is a rough line - a fixation area for some thigh muscles.
• The lower section consists of rounded extensions - it is divided transversely by a wide depression. These parts are called condyles - they are normally covered with articular cartilage and form the upper half of the knee joint.

The head and neck of the femur have a relatively isolated blood supply, which affects the rate of healing when they are damaged.

Soft fabrics

Between the skin with fatty tissue and the muscle tissue of the upper leg there is another large formation - the fascia lata of the thigh. It is a large sheath of connective tissue that collects all the muscles of the anterior and lateral sections into one large bundle. A durable outer shell gives them the support they need, allowing them to work more efficiently and smoothly.

Inside the muscle bundles there are also tendon septa, dividing them into three groups. Each of them performs a certain range of movements during contraction:

1. The anterior group consists of two long and strong muscles - the sartorius and the quadriceps femoris. Their purpose is to flex the leg at the hip joint, as well as extend the knee. The quadriceps muscle in the lower part forms a powerful and wide tendon, which passes through the kneecap to the lower leg.
2. The posterior group is formed by thin and long muscles - biceps, semimembranosus and semitendinosus. On the contrary, they carry out extension at the hip joint and flexion at the knee joint. And with fixed legs, their contraction allows you to return the torso from a tilted position.
3. The internal group consists of small short muscles - the pectineus and gracilis muscles, as well as the adductor magnus, brevis and longus. As a result of their coordinated work, the hip is adducted and rotated outward.

The peculiarity of the thigh muscles is their dual purpose - they take on both powerful static and dynamic loads, often combined with each other.

Vessels and nerves

The vast majority of these formations are located in the space located between the anterior and internal muscle groups. Starting from the upper border, the main vascular bundle passes there, providing blood supply to the entire lower limb. The nerves are divided according to the opposite principle - the largest of them, on the contrary, runs in the back of the thigh.

In general, the arrangement of vessels and nerve bundles is of the main type, characteristic of such a large segment of the limb. Therefore, they should be considered within these highways:

• Arterial vessels are represented by the large femoral artery, which passes to the limb from the pelvic cavity. It runs in the intermuscular cavity along the inner surface of the thigh, giving off a deep branch to supply almost all of the muscles listed above. The main trunk, just above the knee, goes deep into the soft tissues, penetrating the popliteal fossa and extending to the lower leg.
• The venous system consists of two parts - the femoral vein represents its deep part, and the large saphenous vein is a superficial vessel. Just below the inguinal fold they merge, forming a common vein that extends into the pelvic cavity.
• The innervation of the thigh is provided by two systems of nerves located on its opposite sides. Together with the vessels, the femoral nerve emerges on the inner surface. The most powerful similar structure in the body, the sciatic nerve, runs behind it.

The main type of blood supply and innervation makes the legs vulnerable to injury, since if a vessel or nerve is damaged at the hip level, the entire limb suffers.

Knee joint

This rather large and complex articulation cannot be ignored - it is both the boundary and the connecting element between the lower leg and the thigh. Therefore, you should consider all the structures included in its composition:

• There are only two main bone elements in the knee joint - the femoral condyles and the articular surface of the tibia. They bear the main load at rest and during movement.
• But there is also an additional bone - the patella (called the patella due to its external shape), which plays an important dynamic role in the joint.
• Inside the joint cavity there are menisci - two semilunar cartilaginous plates that ensure tight contact of the articular surfaces of the bones. They also provide a good shock absorption effect.
• The ligaments complete the entire structure - they surround the knee on all sides, and are even present inside the joint cavity. Their varied position and direction provide the connection with both good strength and mobility.

The attachment points for the muscles of the leg and thigh are located in areas above or below the knee joint. Despite the fact that they often overlap each other’s actions, this does not cause a negative effect. On the contrary, this structure ensures stabilization of the work of all muscles on the leg among themselves.

Shin

This segment of the lower limb is very similar in external and internal structure to the thigh. The only significant difference is the number of bones included in their composition. On the lower leg, the supporting structures are represented by two similar elements - the tibia and fibula. But the essence remains the same - only one of them bears the main load, transferring it to the foot.

The border between the thigh and lower leg does not touch - these structures are completely separated by the knee joint. Therefore, we should dwell on this issue in more detail:

1. The upper border of the tibia is quite clear - it is a perpendicular plane. It passes through a line drawn 5 centimeters under the lower edge of the patella.
2. The lower border has several clear landmarks separating the lower leg from the foot. The most basic and visible formations, even externally, are the ankles. These bony protrusions, located just above the foot, are the end portions of the lower leg bones. Their lower pole is the starting point - lines are drawn obliquely upward from it to the front and back surfaces, which, when connected, give a clear boundary.

Many people mistakenly classify the ankles as parts of the foot, even though these bony structures are anatomically and functionally an integral part of the lower leg.

Skeleton

The supporting frame of this part of the leg consists of two bones, between which the load is still evenly distributed, despite their different sizes. This feature is due to the large number of soft tissues, which completely eliminate the difference in size towards the lower leg. Therefore, when moving, pressure in the lower part of both bones is perceived equally.

Since each of them plays a specific role in the anatomical structure of the lower leg, they differ significantly in structure. Therefore, it is necessary to consider some of their features:

• The tibia occupies an anterior and internal position on the lower leg - it is its contours that protrude through the skin. In the upper part it has a thickening that forms the lower half of the knee joint. Just below it (under the kneecap) is the tuberosity - the place of muscle attachment. Then comes the main tubular part, which smoothly passes into another thickening at the bottom - the articular surface and the inner ankle.
• The fibula on the lower leg is located on the outside, slightly hidden in the upper segment behind the powerful “neighbor”. It does not participate in the formation of the knee joint, but is only connected to the tibia using strong ligaments. Then it also passes into a thin tubular part, ending at the bottom with a thickening - the outer ankle.

The ankle is often called a favorite place for fractures - a sharp transition from a narrow part of the bone to a widening contributes to the development of damage in this area.

Soft fabrics

All muscles of the lower leg, as well as those of the thigh, are enclosed in strong connective tissue sheaths, ensuring their isolated work. But due to the small size of the area, they do not cover several muscle groups at once, but only hold individual formations. This feature is due to the connection with the foot - individual muscles provide mobility of both the foot and the toes.

For convenience, all muscles are also divided into three groups, taking into account the position of the cases, as well as their own functions. With this division, they resemble the anatomy of the hip even more:

1. The most famous among them is the posterior group, which includes the gastrocnemius and soleus muscles of the leg. Their fibers are closely adjacent to each other, and when fused in the lower part they form a powerful Achilles tendon. Functionally with the posterior tibialis muscle, as well as the long flexor muscles, they represent a single mechanism, providing plantar flexion of the foot and toes during contraction.
2. The anterior group of muscles consists of the tibialis muscle of the same name, as well as long extensor fingers. When contracted, they provide the opposite effect - dorsal extension of the foot along with the toes.
3. The most isolated structure is the outer group, which includes the peroneus longus and brevis muscles. Due to their small size, they do not interact with other muscles, but only perform an auxiliary and stabilizing effect during their contraction.

The muscles of the lower leg are very unequal in size, so injuries to small muscles that cannot withstand sudden loads are quite often observed.

Vessels and nerves

The lower leg, unlike the thigh, relatively loses the main type of blood supply and innervation. Starting from the popliteal fossa, there is a rapid division of blood vessels and nerves into several sections, approximately corresponding to muscle sheaths. Consequently, in this area it is already difficult to identify any large structure:

• A small section of the popliteal artery in the upper segment of the leg, emerging from the fossa of the same name, quickly divides into two trunks. The first of these is the anterior tibial artery, which passes to the corresponding area through the interosseous membrane. The second branch is the posterior tibial artery, which also gives off a branch to the peroneal muscles.
• The venous system is much more interesting - the deep veins completely correspond in location to the arteries of the same name. But the superficial system includes two formations - the great and small saphenous veins, merging in the popliteal fossa. The systems communicate with each other using short perforating veins.
• Innervation of the lower leg is provided by bundles of the powerful sciatic nerve - the tibial and common peroneal branches.

Despite the significant separation of the entire vascular and nervous network, the lower leg is still completely dependent on the main location of these pathways on the thigh. Therefore, even the slightest damage there (especially to the nerve) causes complete loss or decrease in functionality in the underlying sections.