In most cases, sciatica results from a nerve compression in the lower back. The most common cause is a bulging or herniated lumbar disc, or Piriformis syndrome.
Herniation is a displaced fragment of the center part/ nucleus of the disc that is pushed through a tear in the outer layer or annulus of the disc.
Scoliosis is a sideways curve of the spine that causes stiffness and pain. It is called an idiopathic disease because the cause of it is unknown.