How can I tell if I have progressive scoliosis?

Standing xrays. Measirement on standing full length films 6-12 months apart loss of height can be a indicator as well.
Serial x rays. Serial x rays over time. Scoliosis most often progresses most in the adolescent growth period. After skeletal maturity if the curve is over 50 degrees it may progress at about a degree a year. Curves under this typically progress very slowly if at all.