Knee: Structure, Ligaments, and Disorders

The knee is among the most important joints of the body. Knee withstands the all the weight of the body and helps in the movement. The basic function of the knee is to join the thigh to the bone. The knee is considered as the largest joint in human body, the knee joint can be described as a modified hinge joint. The knee joints help in the movement of the body by flexion and extension of the muscle, it also helps in the external and internal rotation which helps in the movement. In this article, we will describe about the intricacies of the anatomy of the knee, knee structure, and the ailments associated with human knee joints bone. This article focuses on articulation, which means the blood supply of the knee.

Knee Structure

The knee can be described as the modified hinge joint it is the largest joint in human body. Sometimes the knee structure is also known as the compound joint of the body because it contains both tibiofemoral and patellofemoral components. Tibiofemoral and patellofemoral are the two articulations found in the human knee body part. The third most important component of the knee structure is the synovial fluid, the synovial fluid is the aqueous component that fills the knee cavity, both the articulations mentioned above are bathed into the synovial fluid. The main function of the synovial fluid is to decrease the resistance to movement by decreasing the friction between the joint thus helps in the movement of the body. 

Articulating Surfaces of the Knee

There are two articular bodies in the knee structure, the articular structure is enclosed within a single joint capsule. It is also important to note that the surface covered by a membrane of hyaline. Hyaline is the cartilage surrounding the joint to provide maximum protection.

Tibiofemoral- It can be defined as the weight bearing component of the knee joint. The tibiofemoral is made up of medial and lateral condyles of the femur bone which joins with the tibial condyles. Medial and lateral condyles of the femur bone diverge slightly distally and posteriorly, there is the presence of involute midpoints, which are located in a spiral fashion. These involute midpoints form the transverse axes. Transverse helps in the motion of the knee structure especially permit the sliding and rolling motion. The tibial condyles are divided by the intercondylar eminence. 

Patellofemoral- It originates from the articulation of the distal femur with the patella of the knee structure. The anterior part of the distal femur specifically attaches to the patella. This articulation allows the tendon of the knee extensor to be inserted directly into the knee from above. The knee extensor is known as the quadriceps femoris. This articulation helps in increasing the efficiency of the knee structure. It is among the important knee facts to understand how this articulation helps in increasing muscle efficiency. The patellofemoral arises and develops inside the quadriceps femoris tendon, it stabilizes the frictional forces placed on femoral condyles. It also helps in increasing the power of the knee extensors by providing them with the fulcrum. 

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Articular Capsule of the Knee Structure

The articular capsule as the name suggests is an enclosing that covers the articular bodies, apart from the presence of articular bodies the main component of the articular capsule includes the synovial fluid and a fibrous membrane. The fibrous membrane is separated by the layer of the fatty deposits. According to the anatomy of the knee structure, the synovial fluid from membranes like structure surrounds the margin of the cartilage both on the femur and the tibia from the anterior end. The synovial membrane is also attached to the femoral condyles, it is to be noted that this attachment is from the behind this results in the production of produces two extensions that are similar to the anterior recess. 

Bursae 

A bursa can be defined as a fluid-filled sac. The bursae can be defined as a sac that is filled with synovial fluid. These are generally found in between the moving structures of the knee joint. The main function of the bursae can be defined as the lubricant of the knee joint. The lubricants work to reduce the wear and tear stress of the knee structure, it is done by reducing the friction between the joints. There are four bursae is found in the knee structure they are as follows, 

1. Suprapatellar bursa

2. Prepatellar bursa

3. Infrapatellar bursa

4. Semimembranosus bursa

Suprapatellar Bursa- It can be defined as the extension of the synovial cavity of human knee joint bones. The suprapatellar bursa location can be defined as the mid-portion in between the quadriceps femoris and the femur.

Prepatellar Bursa- It is located in between the skin and apex of the patella. They are situated below the patellar tendon.

Infrapatellar Bursa- It can be divided into deep and superficial infrapatellar bursa. The deep infrapatellar bursa can be seen located in between the patella ligament and tibia. Similar to the prepatellar bursa the superficial infrapatellar bursa is located in between the skin and the ligament. 

Semimembranosus Bursa- It is situated in the posterior end of the knee. The largest joint in human body is the knee. It is located in between the medial head of the gastrocnemius and the semimembranosus muscle of the knee structure. 

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Menisci

The menisci are defined as the articular disks of the human knee joint bones

The main role of this knee body part is to partially divide the joint space. The articular disk is the fibrocartilage that separates or divides the synovial fluid. The articular disk is generally thin and oval-shaped. This separation is important to ensure the separate movements of the particular parts of the knee. There are two main types of the articular disk are called medial meniscus and the lateral meniscus. They are attached to the intercondylar area of the tibia.  It performs two main functions which are as follows. 

1. They increase the stability of the knee joint by deepening the articular surface of the tibia.

2. They increase the surface area to dissipate the forces, thus acting as a shock absorber. 

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Neurovascular Supply

Neurovascular supply refers to the blood circulation system in the knee structure. Genicular anastomoses are the structure that supplies blood throughout the knees. Genicular branches of the femoral and popliteal arteries are the branches of genicular anastomoses that surround the nearby structures of the knee joint and supply blood to them. Femoral, tibial, and common fibular nerves are found in the knee. One interesting knee facts is that the nerve supply in the knee governed by the Hiltons rules, according to which joint is innervated by the branch of the motor nerve, this nerve branch also supplies a muscle extending across the joints.

Ligaments

There are three main ligaments in the largest joint in human body i.e., the knee. The names of these ligaments are as follows,

1. Patellar ligament

2. Collateral ligaments

3. Cruciate Ligaments

Patellar Ligament- It is the ligament that is attached to the tibial tuberosity. It acts as a continuation of the quadriceps femoris tendon which is distant from the patella.

Collateral Ligaments- These are the strap-like ligaments, their primary role is to stabilize the hinge motion. They prevent excessive lateral or medial motion. It consists of the tibial collateral ligament, which is the medial ligament, and the fibular collateral ligament, which is the lateral ligament.

Cruciate Ligaments- They are the ligaments that connect the tibia to the femur. They are also categorized into anterior cruciate ligament and, posterior cruciate ligament. 

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Movements in the Knee Structure

There are basically four movements that occur in the knee joint, these movements are as follows.

1. Extension, this movement is performed by the quadriceps femoris.

2. Flexion, this movement is performed by the following muscles hamstrings, gracilis, sartorius, and popliteus.

3. Lateral rotation is performed by the biceps femoris

4. Medial rotation, this movement is performed by the five muscles; semimembranosus, semitendinosus, gracilis, sartorius and popliteus.