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Ligament

life science Maturity 11-13 Next article →

A ligament is a specialized type of fibrous connective tissue. Its primary function is to connect one bone to another bone. This connection helps the body form stable joints.

Ligament
Ligament

Ligaments are found in all 30,000 species of amniotes. Amniotes are land animals that have internal bones. In birds and dinosaurs, ligaments also connect flight feathers to bones. While they are similar to tendons and fasciae, their connections are unique. Tendons connect muscle to bone. Fasciae connect muscles to other muscles. Ligaments remain distinct by linking bone to bone.

Ligaments are composed of dense regular connective tissue bundles. These bundles consist of collagenous fibers. Dense irregular connective tissue sheaths protect these bundles. A key characteristic of ligaments is that they are viscoelastic. This means they react to tension in a specific way. When under tension, they gradually strain or stretch. Once the tension is removed, they return to their original shape.

Hypermobility-10
Hypermobility-10

However, they cannot always return to their original state. If they are extended past a certain point or for a long time, they may stay stretched. This is why dislocated joints must be set quickly. If the ligaments lengthen too much, the joint becomes weak. This weakness makes the joint prone to future dislocations.

There are several types of ligaments that provide different kinds of support. Capsular ligaments are part of the articular capsule that surrounds synovial joints. These act as mechanical reinforcements. Extra-capsular ligaments join with other ligaments to provide joint stability. Intra-capsular ligaments are less common. They also provide stability but allow for a much larger range of motion. Some ligaments are even shaped like a cross. These are called cruciate ligaments. In the human knee, the anterior cruciate ligament, or ACL, is very important for stability.

Ligaments play a major role in how we move. Some people have ligaments that are more elastic than average. This condition is known as hypermobility. It is sometimes called double-jointedness.

Hypermobility-10
Hypermobility-10

Because of this elasticity, their joints can stretch and contort further. On the other hand, athletes like gymnasts, dancers, and martial artists perform stretching exercises. They do this to lengthen their ligaments. This makes their joints more supple for movement. However, a broken ligament can cause joint instability. This instability can eventually lead to the wear of cartilage. Over time, this wear may result in osteoarthritis.

Medical science has developed ways to treat ligament injuries. Most ligaments cannot be regenerated naturally by the body. However, there are exceptions. Periodontal ligament stem cells are located near the periodontal ligament. These cells are involved in the adult regeneration of that specific ligament. If a ligament is broken, surgery may be required to stabilize the joint. Sometimes, scar tissue can prevent a successful repair. If a broken ligament cannot be fixed, doctors may use the Brunelli procedure to correct instability. For common injuries like an ACL tear, doctors may perform reconstructive surgery.

In some cases, doctors use artificial ligaments during surgery. These are synthetic materials made of a polymer. A polymer is a type of large molecule. Examples of these materials include polyacrylonitrile fiber and polypropylene. Other materials used include PET, which is polyethylene terephthalate, and polyNaSS. These synthetic options help replace the function of the torn natural tissue. This technology helps restore stability to the skeletal system.

An average adult human body contains about 900 ligaments. They are located in many different areas. In the head and neck, you can find the cricothyroid ligament and the periodontal ligament. The periodontal ligament attaches the cementum of teeth to the alveolar bone. In the thorax, there is the phrenoesophageal ligament. The pelvis contains many ligaments, such as the sacrotuberous and sacrospinous ligaments. The wrist contains the palmar radiocarpal and ulnar collateral ligaments. Even the uterus has ligaments, such as the broad ligament, which is a fold of peritoneum.

Some ligaments are actually remnants of fetal development. These are called fetal remnant ligaments. They form when tubular structures from the fetal period close up. They turn into cord-like structures in the adult. Examples include the ligamentum arteriosum and the ligamentum teres hepatis. The ligamentum arteriosum comes from the fetal ductus arteriosus. The ligamentum teres hepatis comes from the extra-hepatic portion of the fetal left umbilical vein. These structures show how the body changes from a fetus to an adult.

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