The study of ligaments is known as desmology (from Greekδεσμός, desmos, "bond"; and -λογία, -logia).
Ligaments are similar to tendons and fasciae as they are all made of connective tissue. The differences in them are in the connections that they make; ligaments connect one bone to another bone, tendons connect muscle to bone and fasciae connect muscles to other muscles. These are all found in the skeletal system of the human body. Ligaments cannot usually be regenerated naturally, however there are periodontal ligament stem cells located near the periodontal ligament which are involved in the adult regeneration of periodontal ligament.
Capsular ligaments are part of the articular capsule that surrounds synovial joints. They act as mechanical reinforcements. Extra-capsular ligaments join together in harmony with the other ligaments 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 of three.
Ligaments are viscoelastic. They gradually shrink when under tension, and return to their original shape when the tension is removed. However, they cannot retain their original shape when compressed past a certain point or for a prolonged period of time. 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 hypermobility refers to people with more-elastic ligaments, allowing their joints to stretch and contort further; this is sometimes still called double-jointedness.
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.
One of the most often torn ligaments in the body is the anterior cruciate ligament (ACL). The ACL is one of the ligaments crucial to knee stability and is therefore necessary for human mobility. Because of its importance in mobility, it is necessary for the ACL to be repaired promptly with good quality substitutes. This re-constructive surgery has been performed countless times, now new techniques are being used. One of these techniques is the replacement of the ligament with an artificial material. An artificial ligament is a reinforcing material that is used to replace a torn ligament, such as the ACL. Artificial ligaments are a synthetic material composed of a polymer, such as polyacrylonitrile fiber, polypropylene, PET (polyethylene terephthalate), or more commonly used today, polyNaSS poly(sodium styrene sulfonate). Scientists at the Ligament Augmentation & Reconstruction System (LARS) in France have come up with a workable solution to artificial ligaments.
The ACL reconstructive surgery uses a technique called grafting to attach the polymer to the bone. By grafting a bioactive polymer polyNaSS on a polyethylene terephalate device, commonly used in ACL reconstruction, it optimizes the adhesion and distribution of human fibroblasts. In other words the strength and organization of the fibers is increased and the production of fibroblast collagen is increased when the ligament has been bio-integrated with polyNaSS. This new technique is being used on animals and in in-vitro studies today but, the first official medical surgery has yet to occur.
The difficulty behind artificial ligaments is making the polymers biocompatible. Designing the polymer’s properties to be able to withstand all the different types of fatigue is an obstacle that researchers are facing. The polyethylene (PET) and poly (sodium styrene sulfonate) polymers are categorized as Viscoelastic, meaning after the material experiences large amounts of stress it will retain its original properties. Another large issue with biocompatibility and artificial ligaments, is creating a polymer that is non-reactive with inside bodily fluids.
Creating a polymer and coating it with specific substances can make the polymer biocompatible, as well as speed the recovery process. Bio glass 58s, hyaluronic acid, and cationized gelatin are a few coatings that aid the reconstructive process. Bio glass for example is used for strengthening the connection between the polymer and the bone.