what is the most common type of rheumatic disease?
['Osteoarthritis.', 'Rheumatoid arthritis (RA)', 'Lupus.', 'Spondyloarthropathies -- ankylosing spondylitis (AS) and psoriatic arthritis (PsA)', "Sjogren's syndrome.", 'Gout.', 'Scleroderma.', 'Infectious arthritis.']