Structures and Functions of Ligaments

Ligament of Knee

Ligaments are robust fibrous structures that connect two bones or two parts of the same bone. In the human body, some ligaments stabilize specific organs such as the uterus or liver. These important anatomical formations should not be confused with tendons, which connect muscles to bones or other insertion structures.

The ligaments have a stabilizing function, that is, they prevent particular movements or external forces deriving from traumas from altering the position of the structures to which they are connected. In the human body, the ligaments are arranged in such a way as to actively intervene only in the extreme degrees of movement, when the joint is seriously endangered.

Like the tendons, the ligaments are also made up of type I collagen fibers, which have great resistance to the forces applied in traction. Their elasticity is instead reduced: in the knee, for example, the medial collateral ligament has a breaking strength of 276 kg/cm 2 but can only deform up to 19% before breaking. It is also a particularly elastic ligament since, on average; these important anatomical structures are torn if subjected to an elongation that exceeds 6% of their initial length.

The elasticity of the ligaments can, however, increase due to specific stretching exercises; otherwise, the extraordinary degree of joint mobility achieved by the contortionists would not be explained. However, it must be considered that such a level of elasticity is as dangerous as excessive stiffness since it significantly increases joint instability and laxity.

Ligamentous lesions occur when the forces applied to the ligaments exceed their maximum resistance. The ligaments are more susceptible to injury. The faster a force is applied to them. If the trauma is relatively slow, their resistance is such as to detach the small part of the bone to which they are connected (bone avulsion).

The ankle sprain is a classic example of ligamentous injury when we support a bad foot ankle is abruptly moved away from the calcaneus by determining the lesion of the ligaments that hold together these two bones.

Knee Ligaments: What Are They?

The knee is the most complex joint in the human body.

It is also called the femorotibial joint; it acts as a connection between the thigh and calf, connecting the tibia and femur and allowing the legs to bend, rotate and stretch, albeit in a limited way.

The knee is fundamental since the structures that compose it support the weight of the body and allow the man to rise, walk and run; precisely because of its central function in movement. It is subjected to continuous wear and tear and is subject to diseases, malformations, and degenerations.

The knee joint is composed of:

- Bones

- The femur, the upper leg bone (thigh)

- Tibia, the bone of the lower leg

- Patella: a round bone that protects the joint in the front.

- Muscles

- Quadriceps, the anterior muscle tied to the femur

- Biceps femoris, the posterior muscle tied to the femur

- Tibial, the muscle tied to the tibia anteriorly

- Polpliteo positioned transversely and posterior to the knee

- The meniscus

- Сartilaginous structures located between the femur and tibia allow the joint surfaces to slide and slide one over the other, increasing the articular congruity of the tibial plateau and avoiding cartilage wear of the articular structures. We can observe two of them:

- Median

- Lateral

- Ligaments

- Сonnective-fibrous tissue bands that make the joint stable. There are four in all:

- Anterior crusader

- Posterior crusader

- Medial collateral

- Lateral collateral

What They Are and What They Are For

The knee ligaments, as we have just said, are fibrous structures that join the lower end of the femur (distal) to the upper end of the tibia (proximal).

These are made up of 70-80% of Collagen type 1 fiber, particularly resistant to traction, and in a smaller percentage of elastic fibers, very extensible (up to 150% of the length) but not very resistant; this explains why ligaments react well to stretching but not too high loads.

Ligaments perform a very important primary stabilizing function; in fact, they stabilize the joint and prevent its bone components from losing their correct alignment.

In addition, they play a significant proprioceptive role due to the presence of nerve receptors part of the central nervous system, which indirectly regulates muscle tone, posture, balance, coordination, and other activities of the different muscle groups.

The knee ligaments are four:

- Two crusaders, anterior and posterior, which join the lower surface of the distal end of the femur to the upper surface of the proximal end of the tibia, reside in the center of the knee joint. The term "crusader" derives from the cross between the two ligaments to fix the femur and tibia.

- Two collaterals, medial and lateral, take place one on the inside and one on the outside of the knee; they originate from the internal and external lateral surfaces of the distal end of the femur and terminate one on the lateral surface of the proximal end of the tibia (medial ligament) and one on the so-called head of the fibula (lateral ligament).

Let's see them specifically.

Anterior Cruciate Ligament

The anterior cruciate ligament (ACL) is the static stabilizer of the knee and prevents the tibia from sliding forward from the femur; it is the one that limits its movements since it opposes the motion of anterior dislocation of the knee, hyperextension and internal rotation.

It originates in the distal end of the femur, precisely in the area between the intercondylar fossa and the lateral condyle, and ends in the proximal end of the tibia, on the anterior intercondylar tubercle, that is, a particular portion of the tibial plateau.

Posterior Cruciate Ligament

The posterior cruciate ligament (LCP) originates in the distal end of the femur, precisely between the intercondylar fossa and the middle condyle and ends in the proximal end of the tibia attaching itself to a bony prominence called the posterior intercondylar tubercle, located on the tibial plateau in a position more backward than the front one (which is linked to the LCA).

The LCP has the task of preventing the excessive sliding forward of the femur with respect to the tibia and, at the same time, the excessive sliding of the tibia with respect to the femur.

Medial Collateral Ligament

The medial collateral ligament (LCM) arises at the medial epicondyle of the femur and ends on the medial condyle of the tibia. The LCM is also called the internal collateral ligament because it is positioned, as you can guess, on the internal side of the knee.

Its task is to reinforce the inner side of the knee and prevent an excessive thrust on the opposite side from misaligning the femur in the medial direction with respect to the tibia or vice versa.

Lateral Collateral Ligament

The lateral collateral ligament (LCL) arises at the height of the lateral epicondyle of the femur and ends at the head of the fibula, the bone parallel to the tibia, placed on the outside, and thinner than, despite being the end head of a ligament, is not part of the knee joint because it does not communicate with the femur and does not support the weight that the latter unloads on the tibia.

LCL is also known as an external collateral ligament because it is located on the outside of the knee. The task of this ligament is similar to that of its opposite; it, therefore, reinforces the external side of the knee, avoiding the misalignment, in the lateral directionLigament of Knee, of the femur with respect to the tibia or vice versa.

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Apr 23, 2020

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