A collision can do more than bruise muscles; it can destabilize and exaggerate pre‑existing health conditions. For individuals with pre-existing medical conditions, the legal questions are predictable: Will insurers blame my heart history? Will they blame my current pain on that time I broke my arm 15 years ago? What about my osteoporosis and arthritis? Does it matter that I see a therapist for my depression or anxiety? Can I still recover compensation if the crash worsens my condition?
The reality is, yes, insurers and defense lawyers will bring those pre-existing conditions to light. They will try to reduce the severity of your current injuries based on your past health and question what really caused your injuries. But Ontario law has clear answers rooted in causation principles which allow us to shape and mould the information we have regarding your pre-existing conditions and your current injuries.
Key Takeaway: if you have any medical conditions, it’s important to regularly see your doctors, listen to what they say, and follow their recommendations. Giving up on physiotherapy because you feel it’s not working anymore, missing medical appointments, and not following through on your medication is gold for insurance adjusters and defence lawyers. These make it easier for them to argue that your symptoms aren’t related to the collision. The records of your medical visits and the chronology of status updates made by your medical practitioners make or break a case where pre-existing conditions come into play.
A Lesson In Law: “Thin Skull” & “Crumbling Skull” Doctrines
The starting point is causation. What’s the root cause of your injury? Under the tort of negligence, a plaintiff must prove that the defendant’s conduct caused or materially contributed to their injury. When pre‑existing conditions are involved, the Supreme Court of Canada’s decision in Athey v. Leonati 1996 CanLII 183 (SCC) is foundational.
Athey is routinely cited for the difference between “thin skull” (pre‑existing vulnerability that makes damages worse but does not break causation) and “crumbling skull” (a condition that was deteriorating regardless, which may limit damages to the additional harm caused by the tort).
In a nutshell, if you’re injured through someone else’s negligence, the essential purpose and most basic principle of tort law is that the plaintiff must be placed in the position he or she would have been in absent the defendant’s negligence. This is called the “original position.”
At paragraphs 34-36, the court in Athey makes the following statements:
- “The “crumbling skull” doctrine is an awkward label for a fairly simple idea. It is named after the well-known “thin skull” rule, which makes the tortfeasor liable for the plaintiff's injuries even if the injuries are unexpectedly severe owing to a pre-existing condition.”
- “The tortfeasor must take his or her victim as the tortfeasor finds the victim, and is therefore liable even though the plaintiff’s losses are more dramatic than they would be for the average person.”
- “The so-called “crumbling skull” rule simply recognizes that the pre-existing condition was inherent in the plaintiff’s “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.”
- “…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 reducing the overall award.”
Key Takeaway:
- Thin Skull: The defendant must take the plaintiff as they are, even if a pre‑existing condition makes the injury worse.
- Crumbling Skull: If the plaintiff had a condition that would have deteriorated anyway, the defendant is only responsible for the additional harm caused by the their negligence.
If the defendant’s negligence materially contributes to an injury, the defendant is liable for the loss, even if a pre‑existing condition made the outcome worse. The injured person should be put back in their “original position.” Notably, the defendant need not put the plaintiff in a position better than his or her original position.
A Practical Example
Consider an 86-year-old lady. She is fully functional, drives, lives independently, has a rich social life and also walks independently but sometimes needs help with stairs. She has developed osteoporosis in her old age, and her doctor recommends a walker or cane, and also predicts that while she is self-sufficient now, she may need to move into a retirement home or nursing facility in 5 years.
On a Saturday morning she visits a local bakery on the way to visit her children and grandchildren. While walking through the parking lot, a car is reversing out of a parking spot, doesn’t see her, and bumps into her. It isn’t a hard bump, but she loses her balance, falls, and breaks her hip.
On examination, it’s determined that her osteoporosis contributed to the break. The defence lawyer will argue that if she didn’t have osteoporosis, she wouldn’t have broken her hip because the average person who is bumped into will not break their hip.
- The Thin Skull Rule Says: You must take the victim as you find them. In this case, she was found with osteoporosis, and that matters. The osteoporosis didn’t cause the injury; the negligence of the driver did.
Now consider that a few months after the collision, the 86-year-old lady’s condition begins to worsen. She goes from barely relying on her walker to needing it everywhere. A year later she is no longer able to drive. A year and a half later after the collision she is no longer self sufficient and relies on her friends, family, and PSWs for everything. Two years after the collision she speaks to her family and they decide to move her into a nursing facility.
- The Crumbling Skull Rule Says: She was going to become less self sufficient as time went on, but she is placed in a nursing facility 3 years sooner than predicted. The defendant is not liable for putting her in the nursing facility; rather, the defendant is liable for the 3 years she is in the nursing facility, because but-for the negligence of the defendant driver, she would not have been in the nursing facility 3 years sooner.
Bottom Line
Pre‑existing medical conditions do not negate compensation. The law protects people whose injuries are aggravated or accelerated by someone else’s negligence.
Successful claims focus on material contribution, functional impairment, and permanent impact, proven through disciplined documentation and credible medical evidence. If a collision worsened your cardiac health or function, you can recover fair and just compensation for that aggravation.
The law requires defendants to take victims as they find them. JRJ LAW helps clients with pre‑existing conditions build strong, medically grounded claims. We’ll review your records, clarify legal doctrines, and protect your rights while you focus on recovery. Book a free consultation.