Your bones are living tissues that rebuild constantly throughout your life. During childhood and your teens, your body adds new bone faster than it removes old bone. After about age 20, you can lose bone faster than you make bone. There are many kinds of bone problems, such as: osteoporosis, cancer, bone diseases, and fractures.
Your muscles help you move and help your body work. Different types of muscles have different jobs. There are many problems that can affect muscles. Muscle disorders can cause weakness, pain or even paralysis.
A joint is where two or more bones come together, like the knee, hip, and shoulder. Joints can be damaged by arthritis and other diseases, injuries, or other causes.