This content is made possible by our sponsors. Submit your expert blog here.

Do pre-existing injuries affect your current personal injury case?

Imagine a scenario where you sustain injuries due to the negligent actions of another party on a part of your body that was already injured. When filing for damages, the law requires that you disclose all related injuries suffered as well as pre-existing injuries. This is because the negligent party (the tortfeaser) is obliged under Canadian law to return you back to your “original position,” no less and no more.

The Supreme Court has dealt with the issue of injury to a part that was already susceptible to injury (Athey v. Leonatio [1961]) and there well-established principles in tort law to deal with the matter, called the “thin skull” and the “crumbling skull” rules.

The thin skull rule

As outlined by the Supreme Court of Canada, the general rule of negligence is that the tortfeaser is to return the injured party to their original position. This is called the “thin skill” rule. The tortfeaser is liable for the victim’s injury or injuries, even if they have been exacerbated by the pre-existing condition. In other words, even where the injuries are made worse by the pre-existing condition, the negligent party is still obliged to return the injured party back to their “original position.”

In McCarthy v. Davies, the Plaintiff (Shirley McCarthy) was injured in a car accident and she brought forth a claim for damages for loss of income, diminished earning capacity, future care, and pain and suffering. The Plaintiff alleged that the accident had led to chronic pain in the neck, shoulders, back and hips. Although ICBC’s lawyer admitted liability, he argued that the Plaintiff had pre-existing degenerative disc disease, leading to the current injuries. The court applied the think skill principle and ruled that the injuries sustained by the Plaintiff exacerbated her pre-existing condition which was asymptomatic and awarded the Plaintiff $100,000.

In Pelletier v. Ontario 2013 ONSC 6898, the court commented that the “thin skull rule is engaged by a pre-existing physical condition, but it is not limited to physical ailments.” The court also commented that the rule also applies to psychological frailty as well, meaning not only does the tortfeaser have to restore the injured party back to their original physical condition, but also their original psychological condition.

The crumbling skull rule

The crumbling skill rule is the caveat to the thin skull rule. This rule protects the tortfeaser and prevents him from “overcompensating” the injured party. In other words, the rule is supposed to ensure the tortfeaser only returns the injured party to the original condition and not to make an improvement in his/her condition. In Athey v. Leonatio [1961], the Supreme Court stated that “if there is a measurable risk that the pre-existing condition would have detrimentally affected the plaintiff in the future, regardless of the defendant’s negligence, then this can be taken into account.”

In MacIntosh v. Davison, the Plaintiff, James Robert Stewart MacIntosh, was injured in a car accident and he brought forth a claim for damages, including diminished earning capacity, cost of future care, out of pocket expenses, and pain and suffering. The defendant’s lawyers admitted liability and the court awarded $90,000 for pain and suffering, but this amount was reduced by 20 per cent on account of the pre-existing condition (back problems).

Disclose pre-existing conditions

You may be tempted to hide pre-existing conditions when filing a personal injury claim, but avoid this temptation. Failure to adequately disclose the pre-existing injury, illness or other condition can reduce your chances of getting a fair and favorable settlement and it can lead to court sanctions. This is particularly important if the old injury or ailment is in the same place as the new injury.

Medical records are essential

Medical records are important because they lay the ground for discussion about the impact of pre-existing injuries. In case of disability resulting from the injuries, medical records serve to document this disability.

Hire a lawyer

Personal injury lawyers understand the “thin skull” and the “crumbling skull” rules and have the training, skills and experience necessary to not only make a successful argument in your favor but also to get the most out of the defendant or his insurer.

A lawyer will assess your case and guide you on such matters as how much you should seek in compensation and when to settle out of court and when to proceed on trial. Hiring a lawyer allows you to concentrate on your recovery, it ensures that emotions do not cloud your judgment, and it ensures you get adequate representation even without money since a good personal injury lawyer will only be paid if and when they win the claim.

For more than 30 years, Salvatore Grillo has been recognized for helping shape personal injury litigation in the Greater Toronto Area. Mr. Grillo obtained his degree from Osgoode Hall Law School. He can be reached at or 416-614-6000 x2015.