The inner lining of the capsule has a synovial membrane made up of cells that produce a fluid that lubricates the joint. There are six kinds of synovial joint motion. Select one to find out more. Joints allow bones to move relative to each other, and keep the ends of the bones properly aligned. This allows one to bend our knees, wrists, and digits.
Bones change with age.
They become less elastic and more brittle. The joints between bones may become rough as the cartilage wears out. Long bones, like those in your legs and arms, increase in length from growth plates at the end. Bone growth stops when you become an adult. Arthritis means joint swelling, pain, and loss of motion.