A legal theory, companion to the thin skull rule, which limits a tort defendant’s exposure to a plaintiff’s injuries to the plaintiff’s condition at the time of the tort.
In 1996, in Athley v Leonati, the Supreme Court used these words to describe and distinguish the crumbling skull rule:
“The defendant need not put the plaintiff in a position better than his or her original position. The defendant is liable for the injuries caused, even if they are extreme, but need not compensate the plaintiff for any debilitating effects of the pre-existing condition which the plaintiff would have experienced anyway. The defendant is liable for the additional damage but not the pre-existing damage.”
Also, in B (KL) v BC:
“This rule is intended to ensure that the plaintiff is not put in a position better than that which he or she would have been in had the tort not been committed.”
It is distinguished from the thin skull rule as stated in Shaw v. Clark:
“The distinction between a thin skull case and a crumbling skull case is that in the (thin skull), the skull, although thinner than the average skull, is in a stable condition before the accident and, but for the accident, would have remained so.”
"The (crumbling skull) is where the skull, whether thick or thin, is not in a stable condition before the accident but in a state of continuing deterioration which the accident has merely accelerated.”
“In the (crumbling skull), the Defendant is not to be held responsible for the whole of the post‑accident condition of the skull. The Defendant's actions are not to be treated as having been the sole cause of the entire post‑accident condition of the Plaintiff. The Defendant's actions are viewed as merely an aggravating cause. Depending upon the circumstances, the degree of aggravation may range from very substantial to very slight.”
References and Further Reading: