What is Rheumatology of Rheumatologist ?. Rheumatology/Rheumatologist is a subspecialty of medicine which deals with diagnosis and treatment of diseases of bones, joints, muscles, ligaments, tendons and connective tissue. Rheumatological disorders range from chronically disabling arthritis like rheumatoid arthritis and ankylosing spondylitis to multisystem diseases like vasculitis to milder but nagging and persistent pains like chronic back pain & neck pain.