The flexible connective tissue that connects bones to other bones and helps form joints is a ligament.
Ligaments are strong bands of dense connective tissue, rich in collagen fibers. They attach bone to bone, reinforce joints, and limit excessive movement so that bones do not separate, twist too far, or dislocate. Some ligaments are narrow and cord-like, while others form broad sheets around a joint.
A common mix-up is confusing ligaments with tendons. Tendons connect muscles to bones and transmit the force that produces movement; ligaments connect bones to bones and primarily stabilize and guide joints. Cartilage is different again: it cushions joint surfaces, reduces friction, and provides flexible structural support. Bursae are small fluid-filled sacs that reduce friction between moving tissues.
Ligament injuries are called sprains. The anterior cruciate ligament, or ACL, is a familiar example in the knee, while the ankle contains several ligaments that help prevent the joint from rolling excessively. Ligaments can heal, but severe tears may require extensive rehabilitation or surgical reconstruction.