Rheumatologists care for patients with diseases of the joints, muscles, bones and tendons. They diagnose and treat arthritis, back pain, athletic injuries and osteoporosis, and specialize in caring for patients with any of the more than 130 diseases associated with arthritis. Examples of common forms of arthritis and connective tissue diseases include degenerative joint disease (osteoarthritis); rheumatoid arthritis; gout; lupus; ankylosing spondylitis; and scleroderma.