Osteoarthritis is a joint disease that mostly affects cartilage. Cartilage is the slippery tissue that covers the ends of bones in a joint. Healthy cartilage allows bones to glide over each other. It also helps absorb shock of movement. In osteoarthritis, the top layer of cartilage breaks down and wears away. This allows bones under the cartilage to rub together. The rubbing causes pain, swelling, and loss of motion of the joint. Over time, the joint may lose its normal shape. Also, bone spurs may grow on the edges of the joint. Bits of bone or cartilage can break off and float inside the joint space, which causes more pain and damage.
People with osteoarthritis often have joint pain and reduced motion. Osteoarthritis occurs most often in older people. Younger people sometimes get osteoarthritis primarily from joint injuries.
Osteoarthritis usually happens gradually over time. Some risk factors that might lead to it include: being overweight, getting older, joint injury, joints that are not properly formed, a genetic defect in joint cartilage and stresses on the joints from certain jobs and playing sports.