Ligaments are stretchy bands of tissue that, in most cases, hold one bone to another. They are a key part of what allows most joints to move, help control their range of motion, and stabilize them so that the bones move in proper alignment. Some parts of the peritoneum, the membrane that surrounds the abdominal cavity, are also called ligaments although they perform a different function.
Proteins known as collagen make up the tissue in most ligaments. Groups of these proteins form long, flexible, thread-like strands, or fibers. Collagen fibers are found throughout the bodies of humans and other warm-blooded animals, as they help the skin stay elastic and also make up most types of connective tissue. The composition of these fibers allows them to stretch significantly when they move, such as when the elbow is bent or straightened. Collagen fibers are often arranged in crossing patterns, which helps prevent the joint from moving past its normal range of motion despite the ligament's flexibility.
Types and Function
Connective tissues generally serve to protect organs, store energy, support body structures, or connect other tissues. Most ligaments fulfill the last function and help flex or extend a body part; these are called joint or articular ligaments. In the elbow, for example, the ulnar collateral, radial collateral, and annular ligaments work together to allow the joint to move. They are found in the head and neck, pelvis, wrist, and knee, among other places. Each joint typically contains at least three, with the knee having eight.
Other ligaments, such as those found in the back, mainly provide stability to bone or cartilage. If the structure primarily strengthens or supports other ligaments, it is called an accessory ligament.
There are additional structures that are called ligaments even though they do not connect bones. Most individuals, for example, have portions of a tubular structure left over from fetal development known as the fetal remnant ligament. Parts of the peritoneum that are folded together and are found around or between certain organs are called peritoneal ligaments. They surround a number of blood vessels, including the hepatic portal vein to the liver, and support significant parts of the reproductive system in women.
Injuries and Treatments
Sprains are perhaps the most common ligament injury, and occur when this connective tissue is unexpectedly stretched past its normal capacity. This is often mixed up with a strain, which is when a muscle has been stretched too far. Sprains are often caused by sudden and violent movement or by improper stretching techniques. When a ligament is damaged more severely, it can be torn or ruptured, a more serious injury.
Because ligaments play an important role in stabilizing the joints, they are very susceptible to injury due to overuse or sudden movement. Many professional athletes injure the knees, elbows, and shoulders especially as actions taken while running, jumping, and throwing can all damage the joints. The anterior cruciate ligament (ACL), for example, is located behind the knee and often sustains damage through contact-heavy or running sports.
If a ligament is stretched too far too often, the joint will become weaker and less flexible, which can lead to long-term health concerns. Connective tissue also has a relatively low blood supply, so it may take longer to heal. Patients should be careful when engaging in any activities that can put excessive pressure on an injured ligament, as this may cause additional damage.
Injuries may benefit from at-home remedies like icing and rest, which can help relieve swelling and inflammation. Braces can be used to keep the injured body part stable, which can quicken recovery as well. More severe injuries may require physical therapy, where the ligament will be worked through light exercise. Generally, only major issues, such as a tear or rupture, will need surgery.
Regular stretching can increase the length and flexibility of the muscles and by extension the ligaments. This strengthens the joints, helping to prevent injury and allowing them to move farther and support more activity. In extreme cases, this can even allow people to perform seemingly impossible body movements, such as the contortions of an acrobat or the kicks of a martial artist. Some individuals are naturally gifted at extraordinary movement, like so-called double-jointed individuals who have extra-long ligaments that allow their joints to stretch beyond the normal range.
Ligaments are sometimes confused with other, related body tissues. Tendons, for example, connect bones to muscles. Other connective tissue structures — fascia — join muscles, nerves, and blood vessels together. Despite their different functions, all three types are made up of collagen.