About 900 ligaments hold an adult body together, and most cannot regrow
Ligaments are tough bands of fibrous tissue that join bone to bone, and in birds and dinosaurs they also anchor flight feathers to bone. All 30,000 or so species of amniotes have them, an adult human carries about 900, and once badly torn most of them cannot regenerate on their own.
Ligaments, tendons and fasciae are all connective tissue, and they differ in what they link: ligaments tie bone to bone, tendons muscle to bone, and fasciae muscle to muscle. A true ligament is a bundle of dense, regularly arranged collagen fibres wrapped in sheaths of less orderly connective tissue. Some reinforce the capsule around a synovial joint, others sit outside it, and the rarer ones inside the capsule steady a joint while allowing far more movement; cruciate ligaments come in crossed pairs. Some restrict movement or block it outright. Their study has its own name, desmology.
Ligaments are viscoelastic, stretching slowly under tension and springing back when released, but only up to a point. Pulled too far or for too long, they stay lengthened, which is why a dislocated joint should be put back quickly before it becomes loose and prone to slipping out again. People with unusually elastic ligaments are described as hypermobile, the condition popularly called double-jointed, and dancers, gymnasts and martial artists stretch to lengthen theirs.
A snapped ligament can leave a joint unstable, and over time that instability can wear down cartilage and lead to osteoarthritis. Not every tear needs an operation. The anterior cruciate ligament, vital to knee stability, is among the most often torn and is frequently rebuilt surgically, sometimes with synthetic polymers such as polypropylene or PET. When repair fails, methods such as the Brunelli procedure can restore stability.
The name also covers other structures: folds of the abdominal lining such as the broad ligament of the uterus, cords left behind by closed fetal vessels, and the periodontal ligament that fastens teeth into their sockets and has its own stem cells.
Source: Ligament
