Ligament
In anatomy, the term ligament is used to denote three different types of structures:[1]
- Fibrous tissue that connects bones to other bones. They are sometimes called "articular larua"[2], "fibrous ligaments", or "true ligaments".
- A fold of peritoneum or other membranes
- The remnants of a tubular structure from the fetal period of life
The first meaning is most commonly what is meant by the term "ligament". After briefly discussing the other two types of ligaments, the remainder of this article will focus upon the first type.
Peritoneal ligaments
Certain folds of peritoneum are referred to as ligaments.
Examples include:
- The hepatoduodenal ligament, that surrounds the hepatic portal vein and other vessels as they travel from the duodenum to the liver.
- The broad ligament of the uterus, also a fold of peritoneum.
- The suspensory ligament of the ovary
Fetal remnant ligaments
Certain tubular structures from the fetal period are referred to as ligaments after they close up and turn into cord-like structures:
| Fetal | Adult |
| ductus arteriosus | ligamentum arteriosum |
| extra-hepatic portion of the fetal left umbilical vein | ligamentum teres hepatis (the "round ligament of the liver"). |
| intra-hepatic portion of the fetal left umbilical vein (the ductus venosus) | ligamentum venosum |
| distal portions of the fetal left and right umbilical arteries | medial umbilical ligaments |
Articular ligaments
In its most common use, a ligament is a band of tough, fibrous dense regular connective tissue comprising attenuated collagenous fibers. Ligaments connect bones to other bones to form a joint. They do not connect muscles to bones; that is the function of tendons. Some ligaments limit the mobility of articulations, or prevent certain movements altogether.
Capsular ligaments are part of the articular capsule that surrounds synovial joints. They act as mechanical reinforcements. Extra-capsular ligaments join together and provide joint stability. Intra-capsular ligaments, which are much less common, also provide stability but permit a far larger range of motion. Cruciate ligaments occur in pairs.
Ligaments are elastic; when under tension, they gradually lengthen, unlike tendons which are inelastic. This is one reason why dislocated joints must be set as quickly as possible: if the ligaments lengthen too much, then the joint will be weakened, becoming prone to future dislocations. Athletes, gymnasts, dancers, and martial artists perform stretching exercises to lengthen their ligaments, making their joints more supple. The term double-jointed refers to people who have more elastic ligaments, allowing their joints to stretch and contort further. The medical term for describing such double-jointed persons is hyperlaxity and double-jointed is a synonym of hyperlax.
The consequence of a broken ligament can be instability of the joint. Not all broken ligaments need surgery, but if surgery is needed to stabilise the joint, the broken ligament can be repaired. Scar tissue may prevent this. If it is not possible to fix the broken ligament, other procedures such as the Brunelli Procedure can correct the instability. Instability of a joint can over time lead to wear of the cartilage and eventually to osteoarthritis.
Examples
Knee
- Anterior cruciate ligament (ACL)
- Lateral collateral ligament (LCL)
- Posterior cruciate ligament (PCL)
- Medial collateral ligament (MCL)
- Cranial cruciate ligament (CrCL) - quadruped equivalent of ACL
- Caudal cruciate ligament (CaCL) - quadruped equivalent of PCL
Head and neck
Pelvis
- Anterior sacroiliac ligament
- Posterior sacroiliac ligament
- Sacrotuberous ligament
- Sacrospinous ligament
- Inferior pubic ligament
- Superior pubic ligament
- Suspensory ligament of the penis