Get to know arthritis by the numbers. You’ll be surprised to find out that arthritis is all around us, and its impact on individuals around the world is more serious than most people realize. According to the Arthritis Foundation, Arthritis is the nation’s Number one cause of disability, affecting approximately 350 million people worldwide. Arthritis is defined as the condition that causes pain and inflammation in your joints. Arthritis manifests itself in several painful, limiting ways, and attacks all kinds of patients, even young children and babies. The most common joints affected by arthritis are the hands, spine, knees, and hips.