Source: https://www.hlaw.ca/judgment-summary/causation-and-pre-existing-conditions/
Timestamp: 2019-04-22 22:49:44+00:00

Document:
While having my injuries examined, it is discovered that I have a pre-existing condition that may be related to injuries – how does this affect my claim?
In the case of Chow v Goodman (2016 BCSC 1486) the plaintiff, a CRA accountant, sustained injuries to his back as a result of two motor vehicle crashes. Very soon after the crashes the plaintiff started to develop numbness and shaking in his extremities requiring him to undergo a discectomy. Although the procedure helped alleviate the plaintiff’s symptoms, the plaintiff’s life was radically altered by the injuries, affecting both his vocational and non-vocational activities. During his examinations leading up to surgery, it was discovered that the plaintiff had a pre-existing degenerative spinal condition that the defence argued was the real cause of the back injuries and not the crashes. Very quickly the case became a battle of the experts with consideration of the thin-skull and crumbling skull principles of causation. The plaintiff’s experts argued in support of the thin-skull principle, asserting that the crashes aggravated and accelerated the pre-existing degenerative spinal condition which, but for the crashes, would not have become symptomatic until much later in the plaintiff’s life. On the other hand, the defence’s experts opined in favour of the crumbling-skull principle, suggesting that the spinal condition would have developed the way it had regardless of the crashes and therefore was not attributable to the defendant’s negligence. In balancing the expert opinions, Duncan J., reviewed the main principles of causation while deciding to favour the plaintiff’s expert evidence over the defendant’s.
 Determining the cause of loss and damage must be kept separate from the assessment of damages to compensate for that loss and damage, since different principles govern the two questions: A. (T. W. N.) v. Clarke, 2003 BCCA 670, 22 B.C.L.R. (4th) 1 at para. 16. Causation concerns whether the accident caused the pre-existing condition to be activated or aggravated. The assessment of damages considers whether there was a measurable risk that the pre-existing condition would have detrimentally affected the plaintiff in the future, regardless of the defendant’s negligence: Hosak v. Hirst, 2003 BCCA 42, 9 B.C.L.R. (4th) 203 at para. 10.
 Causation is established where the plaintiff proves to the civil standard on a balance of probabilities that the defendant caused or contributed to the injury: Athey v. Leonati,  3 S.C.R. 458 at para. 13, 140 D.L.R. (4th) 235.
 The Supreme Court of Canada considered the principles that apply to causation in Resurfice Corp. v. Hanke, 2007 SCC 7,  1 S.C.R. 333. The “but for” test applies, except in very limited circumstances. Mr. Barnes bears the burden of showing that, but for the negligent act of the driver, the injuries of which he complains would not have occurred. In special circumstances, the law has recognized exceptions to the basic “but for” test and applied a “material contribution” test: see Resurfice at paras. 24-25. Those circumstances do not apply in this case. See also Bohun v. Sennewald, 2008 BCCA 23, 77 B.C.L.R. (4th) 85, a medical malpractice case.
 However, neither test requires that the plaintiff establish that the defendant’s negligence was the sole cause of the injury. A defendant is liable as long as he or she is part of the cause of an injury, even though his or her act alone was not enough to create the injury: Athey at para. 17.
 There is no reduction of liability because of the existence of other preconditions. The defendants remain liable for all injuries caused or contributed to by their negligence: Athey at para. 17. A non-tortious cause that precedes the accident but contributes to the injury, a precondition, is not relevant to causation unless symptomatic at the time of the accident: Larwill v. Lanham, 2003 BCCA 629, 190 B.C.A.C. 13 at para. 22. Even if a minor impact causes the plaintiff’s symptoms, it is no answer for the defendant to say that the plaintiff was peculiarly vulnerable to injury because of a pre-existing susceptibility: Rai v. Wilson (1999), 120 B.C.A.C. 122 at para. 6, 196 W.A.C. 122.
 The law does not excuse a defendant from liability merely because other causal factors for which he or she is not responsible also helped produce the harm. It is sufficient that the defendant’s negligence was a cause of the harm: Athey at para. 19.
 The finding of a contribution outside of the de minimis range is a material contribution and sufficient to render the defendant fully liable for the damages: Athey at para. 44. The British Columbia Court of Appeal clarifies in Sam v. Wilson, 2007 BCCA 622, 78 B.C.L.R. (4th) 199 at para. 109 that “material contribution”, as used in Athey, is synonymous with “substantial connection”, as used in Resurfice, and should not be confused with the “material contribution test”.
 The issue in Hosak v. Hirst, 2003 BCCA 42, 9 B.C.L.R. (4th) 203 was whether the accident activated or aggravated a pre-existing but asymptomatic degenerative condition of the plaintiff’s cervical spine, spondylosis. Madam Justice Rowles explains at para. 70 that the plaintiff has to establish that the accident caused or contributed to the activation or aggravation of the pre-existing spondylosis. The plaintiff does not have to show that it was the only cause, but that it was a cause. Once the burden of proof is met, causation must be accepted as a certainty. Loss cannot be apportioned according to the degree of causation where the loss is created by tortious and non-tortious causes: Hosak at para. 71.
 The defence does not dispute that the two accidents caused the plaintiff’s soft tissue injuries, but argues that the plaintiff has failed to prove that the accidents caused or contributed to the need for the plaintiff to undergo the discectomy. The defence argues the plaintiff’s pre-existing disc condition would have become symptomatic without the accident, perhaps within a few years of the accident.
 I accept that at the time of the First Accident, the plaintiff had pre-existing degenerative changes in his neck. These were first detected by Dr. Milton Wong in imaging taken after the plaintiff’s earlier accidents. There is no record the plaintiff had any neurological symptoms, such as limb or hand numbness or buckling legs, between the fall of 2007 and the First Accident.
 The First Accident resulted in a reappearance of neurological symptoms, including left-sided numbness. Dr. Milton Wong noted an increase in the disc protrusion since the earlier accidents and referred the plaintiff to Dr. Sahjpaul. Before the Second Accident, Dr. Sahjpaul detected cord signal changes and recommended surgery.
 Both Dr. Milton Wong and Dr. Sahjpaul are of the opinion that the First Accident triggered the need for surgical intervention much earlier than would otherwise have been the case. Dr. Peter Wong, on the other hand, attributed no significance to either the First or the Second Accident because of his opinion that the plaintiff was on a fairly rapid and inexorable path to deterioration as a result of his spinal stenosis, disc bulge and disc deterioration.
 I accept the opinions of Dr. Milton Wong and Dr. Sahjpaul that the First Accident triggered neurological symptoms and prompted the need for surgery. Dr. Milton Wong has decades of clinical experience as a neurologist. He testified he has never seen a young man whose spondylitic changes had progressed as quickly as the plaintiff’s, in the absence of trauma. He did not believe the natural progress of deterioration would work that fast.

References: v. 
 v. 
 v. 
 v. 
 v. 
 v. 
 v. 
 v. 
 v.