Ligaments hold the human skeleton together. They make a crucial contribution to the stability of the body, and anyone who has ever had the painful experience of tearing a ligament knows about their important role in the musculoskeletal system.
What are ligaments?
There are two different definitions for the term ligament, or ligament: The commonly known one describes the ligaments of the musculoskeletal system, or joint ligaments. These are firm, barely stretchable strands of connective tissue that connect two bones. It is important to distinguish them conceptually from tendons – these connective tissue end pieces of a muscle transmit its pull to the skeleton. Ligaments, on the other hand, have nothing to do with muscles, but connect bones exclusively. Also called ligaments are certain connective tissue tracts in the chest and abdomen that fix internal organs in place.
Anatomy and structure
The anatomy and structure of ligaments can be well illustrated using a twine: The individual fibers point approximately in the same direction, and their quantity makes the twine tear-resistant and resilient; however, it has little tensile strength. The situation is similar with the tapes. They consist of tight parallel fibrous connective tissue. In contrast to other types of tissue, connective tissue contains relatively few cells but a lot of extracellular matrix. This intercellular substance determines the properties of the particular type of connective tissue. In the case of tight parallel fibrous connective tissue, it contains many collagen fibers. Collagen molecules assemble into fibrils. These in turn form larger fibers, which ultimately – tightly packed and aligned in parallel – produce a ligament. This structure ensures that joint ligaments are very resilient and can only be stretched by about 5%. The ligaments of the internal organs have a similar structure, but differ in their much finer structure and lower strength. They may contain conduits such as blood vessels and nerve cords. They are also covered by serosa, which is the layer of tissue that lines the large body cavities.
Functions and tasks
The function and tasks of ligaments vary according to their structure and anatomic location. Their common purpose is to prevent stretch damage to muscles and tendons by preventing unphysiological movement of joints. The so-called adhesive ligaments serve to hold two or more bones together in a joint in a stable manner. To perform this stabilizing function, they must be permanently taut and can only be located at the ends of the axis of rotation so as not to impede movement. If a ligament has the function of preventing unphysiological hyperextension of the joint, it is called an inhibition ligament. It is untensioned in most joint positions, but can tighten in certain extreme positions, limiting range of motion to protect surrounding anatomical structures (for example, finger joints cannot be extended indefinitely). Another function is to direct joint motion in a specific direction. This is what the guiding ligaments do. Normally, the ligaments span externally around the joint, but sometimes they lie as internal ligaments within the joint capsule, such as the cruciate ligaments of the knee.
Diseases
There are a variety of diseases and conditions that can occur in relation to the ligaments. Calcium deposits can form within the ligaments due to overuse or inflammatory processes. In the rheumatic disease ankylosing spondylitis, for example, the longitudinal anterior ligament of the spine calcifies, which can cause it to become completely immobile in the final stage. Such degenerative processes not only impair the function of the affected ligaments, but also damage the entire joint, often affecting bones, nerves and other structures. Ligament damage also frequently occurs as a result of trauma, for example in sports accidents. Injuries vary in severity: a ligament does not have to tear completely; it can also merely be overstretched or partially torn. The cruciate and collateral ligaments of the knee joint and the external ligaments of the ankle joint are particularly frequently affected by such injuries. The latter are particularly at risk in the case of so-called inversion-supination trauma, i.e. when the foot twists inwards, which is the most common sports injury of all.In addition to the ligament, local blood vessels tear, which leads to bleeding into the surrounding tissue and thus to painful swelling. Torn ligaments are usually treated conservatively by elevation, cooling and rest. In particularly severe cases, surgery with possible ligamentoplasty is resorted to.
Typical and common conditions
- Strain of the ligament (ligament strain)
- Torn ligament
