Ligaments are the connective tissues in joints that that connect bone to bone. They differ from tendons in that tendons connect muscle to bone. Ligaments are primarily made of collagen. Ligaments such as the anterior cruciate ligament (ACL) of the knee are an essential component of the body’s joints, providing both stability and movement. Inflammation of ligaments can be the cause or result of many arthritic conditions including osteoarthritis, bursitis, and ankylosing spondylitis.