Athey suffered back injuries in two successive car accidents, and soon after experienced a disc herniation during a stretching exercise. A mixture of the injuries from the two accidents and a preexisting condition caused this.
- Did the injuries suffered in the car accidents merely make it more likely that the herniation would occur, or did they cause them and the "thin skull" rule applies as a result of the predisposition?
Major, writing for the court, goes through all of the defences forwarded by the respondents but concludes that he must take Athey as he finds him, and therefore is liable for all of the injuries. The preexisting condition would not have caused the herniation but for the respondents' actions, it simply made the resulting damages worse – this is an application of the "thin skull" rule. In cases like this you cannot limit liability like you can in cases where there are two tortfeasors partially responsible for the outcome, because the preexisting condition played no part in "causing" the overall injury.
When preexisting conditions would not have caused the injury but for the defendant's actions, then it is the "thin skull" rule that applies and the defendant will be totally liable for the plaintiff's losses.