What are ligaments?

Structure and Functions

Structurally, ligaments appear to be strap-like bands or round cords. They are strong yet somewhat pliable. In terms of the musculoskeletal system, they serve to stabilize the adjoining bones making up what is referred to as an articulating joint. Ligaments consist of a cellular component called fibroblasts, making up 20 percent of their total tissue volume. The remaining 80 percent of the tissue volume is outside the fibroblast cells and consists of collagen and elastin. The relative proportion of collagen to elastin varies among ligaments. The degree of stabilization also varies and depends on each particular joint, such as shoulder and ankle joint ligaments. This degree of stabilization may be one which limits the amount of movement or prevents certain movements entirely. Some ligaments surround an entire joint filled with a lubricating fluid called synovium and are termed capsular ligaments. Ligaments located outside this joint capsule are called extracapsular and provide joint stability, while ligaments located inside the capsular ligament are called intracapsular and permit much more movement of the joint.

Other locations outside the musculoskeletal system that consist of ligaments for supporting structures include the broad ligament for the uterus and Fallopian tubes, which attaches these organs to the pelvic wall. Suspensory ligaments are also found in the body supporting a variety of organs, including the eyeball and breasts.

Disorders and Diseases

Ligaments are elastic, and they gradually lengthen when under tension. The term sprain
describes an injury to a ligament caused by forces that stretch some or all of the ligament’s fibers beyond their limit. This type of ligament injury can result in some degree of rupture of some or all of the fibers. In some instances, the ligament injury includes the possibility of pulling attachments from the bones. The classification for grading ligament injuries is based on two factors, the numbers of fibers ruptured and the resulting instability of the joint involved. Ligament injuries are also classified clinically as first degree (mild), second degree (moderate), or third degree (severe).

A consequence of a stretched or ruptured ligament can be instability of the joint. Not all injured ligaments require surgery, but if surgery is needed to stabilize the joint, the torn ligament can be repaired. Instability of a joint can, over time, lead to wear to the cartilage and eventually to osteoarthritis.

Joint inflammation from trauma or other medical reasons can stiffen the joint ligaments, resulting in restricted motion. In contrast, a group of rare inherited diseases called Ehlers-Danlos syndrome can lead to abnormal collagen, resulting in loss of joint stability because of laxity in the joint capsule.

Several immune diseases can affect the ligaments of the body’s joints. Rheumatoid arthritis is a chronic disease that affects the synovial
membrane of the joint, which produces the joint’s lubricant synovium. This fluid becomes thickened and fleshy and erodes the joint structures, including the articular ligaments.

Perspective and Prospects

The discovery of joint structures is credited to early anatomists such as Andreas Vesalius, who published De fabrica humana in 1543. Until this time, his contemporaries had claimed that ligaments and tendons were types of nerve units. Three centuries later, in 1858, Henry Gray’s writings on dissection, Gray’s Anatomy, described and illustrated the anatomy and function of the human body, including the role of ligaments.

Advances in orthopedic medicine and the development of sports medicine have introduced specific braces to protect major joint ligaments during athletic and nonathletic activities. In addition, the continuing development of surgical procedures for the repair of damaged ligaments can help the individual return to an optimal level of function after the ligament injury. Research is ongoing to provide information to treat and find a cure for the many pathologies that affect ligaments and associated connective tissues.

Bibliography

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MedlinePlus. "Sprains and Strains." MedlinePlus, June 24, 2013.

Norkin C. C. Joint Structure and Function. 4th ed. Philadelphia: F. A. Davis, 2005.

Scuderi, Giles R. Sports Medicine: A Comprehensive Approach. 2d ed. Philadelphia: Mosby/Elsevier, 2005.

Gray, Henry, H. V. Carter, et. al. Gray’s Anatomy. 15th ed. London: Bounty, 2012.

Vorvick, Linda J. "Tendon vs. Ligament." MedlinePlus, August 14, 2012.