A lumbar orthosis that includes first and second, separate, opposing and mating front attachment panels; and a separate, laterally adjustable, rigid lumbar compression piece configured for positioning only at the rear of a wearer, wherein pulling of a cord causes the brace both circumferentially to tighten and to concentrate compression and pressure of the separate, laterally adjustable, rigid lumbar compression piece directly and especially upon a spinal region of a wearer's back with the aid of a mechanical advantage dependant upon a number of apertures through which the cord or cords pass. An orthosis and method for correcting lumbar and thoracic back pain and disorders is also disclosed.