In Karber/Interstate Air v. Industrial Commission, 180 Ariz. 411, 885 P.2d 99 (App. 1994), the claimant suffered a compensable right knee injury. While receiving treatment, he tripped. In order to protect his injured right knee, the claimant placed his full weight on his left leg. His left leg gave way and he fell, injuring his left knee. The ALJ concluded that the claimant's left knee injury was a compensable consequence of the industrial right knee injury. Id. at 412, 885 P.2d at 100. On appeal, this court affirmed, cautioning that although medical causation is required, . . . it is not the exclusive element in determining whether a substantial causal relationship exists between the work injury and the later injury. The ALJ . . . must address legal causation - whether as a matter of policy, the causal connection between the two injuries is strong enough for the . . . subsequent injury to be a compensable consequence of the industrial injury. Id.at 414, 885 P.2d at 102.