Scoliosis, or curvature of the spine, affects 2 to 3 percent of the population in the United States, or about 6 million people, the A.D.A.M. Medical Encyclopedia reported in 2009. Scoliosis most often appears between ages 10 and 15 and affects about 10 percent of all adolescents, although only about 1 percent require treatment. Between 1964 and...