In Cassey v. Industrial Commission, 152 Ariz. 280, 283, 731 P.2d 645, 648 (App. 1987) the Court stated an employee "must establish the disabling effect of the industrial injury in order to establish a permanent impairment. This is true when residual pain is the permanent injury because pain is compensable as an impairment only when it is disabling." Although the court in Cassey described "residual pain" as an "injury," it did not define the term "injury" nor address whether such pain is an injury for the purpose of article XVIII, 8, but instead considered whether disabling pain was relevant in determining the employee's degree of impairment. 152 Ariz. at 281, 283, 731 P.2d at 646, 648 (employee had chronic "thoracolumbar sprain").