The rheumatologist is the doctor who specializes in the diagnosis and treatment of diseases that affect the joints, muscles, tendons and bones.
A physiatrist is a doctor who specializes in diseases that affect the brain, spinal cord, nerves, bones, joints, ligaments, muscles and tendons and is responsible for restoring lost abilities due to illness or injury.
The orthopedist is a doctor who specializes in the skeletal muscle system of the human body including bones, joints, ligaments, tendons, muscles and nerves.