Reasons were released today by the BC Court of Appeal criticizing the phrase ‘crumbling skull’ and spelling out the analysis a Court must take when dealing with non tort related causes to a Plaintiff’s position.
In the recent case (Gordon v. Ahn) the Plaintiff was injured in a 2009 collision and was awarded $50,000 at trial. In reaching the award the trial judge noted that the plaintiff was a ‘crumbling skull’ and further that she failed to mitigate her damages and reduced the damage assessment by some unspecified amount. The BC Court of Appeal ordered a new trial noting the trial judge did not properly address the evidence to justify any reductions. In discussing what is needed of a Court when deciding what position a plaintiff would be in but for the tort the following reasons were provided:
 The use of the phrase “crumbling skull” to describe a plaintiff’s condition is, in any event, rarely helpful. As Major J. explained in Athey, there are no special rules or analyses that apply to claims made by plaintiffs who, before becoming victims of a tort, are affected by conditions that may deteriorate in the future. Damages are always to be assessed by reference to the situation that the plaintiff would be in but for the wrongdoing. Describing a plaintiff as coming within the “crumbling skull doctrine” does not eliminate the need for a complete analysis of the pain and suffering caused by the accident.
 The judge found that there was “an inter-relationship between the pain that the plaintiff experienced from her physical injuries and her emotional or psychological problems”. He also found that her psychological problems “worsened because of the accident”. Even in cases where a plaintiff is suffering from serious chronic depression, an aggravation of the symptoms attributable to a tort is compensable: Sangha v. Chen, 2013 BCCA 267. In the present case, where the plaintiff’s symptoms were fairly minor before the accident, but developed into major depression as a result of the accident, it is clear that damages ought to have been awarded.
 It is not apparent, from the judge’s reasons, whether he awarded any damages in respect of the depression brought on by the accident. Beyond referring to the “crumbling skull doctrine”, he did not undertake any analysis of the issue of damages in relation to Ms. Gordon’s emotional and psychological deterioration.
 A proper analysis of the issue would have required the judge to consider the degree to which Ms. Gordon’s psychological and emotional health was damaged by the accident. Such an analysis would have required a detailed consideration of her pre-accident and post-accident mental health, as well as an assessment of the likelihood that a deterioration would have occurred even in the absence of an accident (see Laidlaw v. Couturier, 2010 BCCA 59). The judge failed, in this case, to undertake such an analysis.
Reasons for judgement were released this week by the BC Court of Appeal confirming that judges must award damages when pre-existing conditions are aggravated in part due to a tortious cause.
In this week’s case (Sangha v. Chen) the Plaintiff was involved in a 2005 intersection crash. Both the Plaintiff and Defendant were at fault for the incident. The trial judge assessed damages on the basis that the Plaintiff sustained a two year soft tissue injury. At the time of trial the Plaintiff had on-going chronic pain which was rooted in chronic depression which pre-dated the accident. However, the Court found that the collision physical injuries “aggravated his previous depressed state” but did not assess damages for the on-going worsened depression finding that the Plaintiff “would have suffered his current symptoms in any event“.
In finding that this was in error and that damages needed to be assessed to reflect the collision caused aggravation of pre-existing depression the BC Court of Appeal provided the following reasons:
 With respect, it does not appear to me to have been open to the judge to find, as she did in para. 110 that Mr. Sangha “would have suffered his current symptoms, in any event”, having found earlier in that same paragraph that “his physical injuries aggravated his previous depressed state”. Further, her conclusion that Mr. Sangha would have suffered his current symptoms appears to be inconsistent with her view expressed in para. 111 that “at most the injuries suffered in the accident aggravated the plaintiff’s mood symptoms”. Given that the “mood symptoms” are exactly those symptoms encompassed within the pre-existing condition of depressive illness, para. 111 appears to allow for attribution of at least a portion of Mr. Sangha’s current symptoms to the physical injuries sustained in the accident.
 I recognize that one must not parse a trial judge’s reasons for judgment with too much exactitude, and so I have turned to the evidence relied upon by the trial judge, the medical report of Dr. Riar, in her determination that all of Mr. Sangha’s current malady derives from his pre-existing condition. Nowhere in that report does Dr. Riar entirely dissociate the current condition of Mr. Sangha from the accident, so as to support the judge’s conclusion that Mr. Sangha would have suffered his current symptoms, in any event. While Dr. Riar clearly considered that the preponderance of Mr. Sangha’s current symptoms derive from the pre-existing mental illness, Dr. Riar also said “I feel that the accident in question aggravated his mood symptoms, which in turn fed into his pains, and they have continued like that all along” and “The only thing the accident did was complicate his situation somewhat more”. Questioned about this, Dr. Riar affirmed this view of the reflection to at least a small degree, of the physical injuries in Mr. Sangha’s current malady:…
 The correct approach to pre-existing conditions is discussed in Athey v. Leonati,  3 S.C.R. 458, under the rubric of “crumbling skull:
The so-called “crumbling skull” rule simply recognizes that the pre-existing condition was inherent in the plaintiff’s “original position”. 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: Cooper-Stephenson, supra, at pp. 779-780 and John Munkman, Damages for Personal Injuries and Death (9th ed. 1993), at pp. 39-40. Likewise, 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: Graham v. Rourke, 74 D.L.R. (4th) 1; Malec v. J. C. Hutton Proprietary Ltd., 169 C.L.R. 638; Cooper-Stephenson, supra, at pp. 851-852. This is consistent with the general rule that the plaintiff must be returned to the position he would have been in, with all of its attendant risks and shortcomings, and not a better position.
 I also refer to Blackwater v. Plint, 2005 SCC 58,  3 S.C.R., 2005 SCC 58.:
 It is important to distinguish between causation as the source of the loss and the rules of damage assessment in tort. The rules of causation consider generally whether “but for” the defendant’s acts, the plaintiff’s damages would have been incurred on a balance of probabilities. Even though there may be several tortious and non-tortious causes of injury, so long as the defendant’s act is a cause of the plaintiff’s damage, the defendant is fully liable for that damage. The rules of damages then consider what the original position of the plaintiff would have been. The governing principle is that the defendant need not put the plaintiff in a better position than his original position and should not compensate the plaintiff for any damages he would have suffered anyway: Athey. …
 I respectfully conclude that the judge erred in failing to reflect, in her damages award, her conclusion of fact that “the physical injuries aggravated his previous depressed state” and “the accident did cause at least some of” the psychological symptoms. To what extent the damages should have been adjusted to account for these conclusions I cannot say. That question is one particularly within the purview of a trial judge. Accordingly, in my view, the award of damages must be set aside and the issue of quantum of damages must be remitted to the Supreme Court of British Columbia for fresh assessment.
The BC Court of Appeal released reasons for judgement yesterday addressing the difficulty of assessing damages for personal injuries to the spine when a pre-existing deteriorating condition is in play.
In yesterday’s case (Bouchard v. Brown Bros. Motor Lease Canada Ltd.) the Plaintiff was involved in a 2005 rear-end collision. He was faced in an awkward position when his vehicle was struck and he sustained injuries.
Although there was competing medical evidence, the Court ultimately found the collision was a cause of a L4-5 disc herniation which required bilateral discectomies and foraminotimies at the L4-L5 and L5-S1 levels of the spine. The Court found that while the collision was a cause of the injury, that there was “a very significant risk” that the Plaintiff’s back problems would have developed even absent the collision and the damages were reduced by 40% to take this risk into account. The BC Court of Appeal held that this reduction was too drastic and reduced the global damages by 20% instead of 40%. In doing so the Court provided the following reasons:
 The vagaries of analyzing and predicting the deterioration of the human spine as it ages are a source of difficulty not only for the medical profession but for anyone involved in resolving personal injury claims. This appeal reflects that difficulty: it involves a plaintiff who at the age of 20 was diagnosed with a narrowing of the L5-S1 disc, then experienced a period of apparent recovery, and then suffered an injury in a motor vehicle accident in 2005 that was found to have been a “significant factor contributing to the herniation of [his] disc at L4-L5, and the development of … symptoms of severe and disabling lower back pain”. No challenge is made to this finding of causation. Rather, the plaintiff challenges the trial judge’s conclusion that there was a “very significant risk” he would have “gone on to suffer serious low back problems” in the absence of the injury in 2005, and that therefore, all the damages that would otherwise have been awarded against the defendants should be reduced by 40%…
 I agree that it was open to the judge to reduce those damages which were awarded in respect of future loss, to reflect the possibility that “ultimately”, Mr. Bouchard would in any event have experienced serious lumbar problems. There was, however, no evidence to suggest that absent the 2005 accident, Mr. Bouchard would have experienced serious and symptomatic degeneration of the spine at the age of 31 (his age at the date of trial) or within a brief time thereafter. Indeed, all the expert evidence suggested such deterioration occurs gradually, subject to specific incidents such as the one that occurred in October 2007. Dr. Hepburn used the word “ultimately” and was not asked to elaborate. Had he been asked, I expect he would have said that one cannot predict with certainty at what age disc degeneration would (or might) have become symptomatic and disabling to Mr. Bouchard, or even that it would necessarily have done so by a particular age.
 Similarly, the trial judge did not describe any time line over which he found there was a 40% chance Mr. Bouchard’s spine would have degenerated to its present state. Obviously, the process could not be projected with exactitude, but the reduction of damages by 40% suggests a very steep upward line on a graph. That line is contrary to the notion of gradual deterioration. If there was a 40% chance Mr. Bouchard would have deteriorated to his present condition by, say, age 50, the chance between ages 31 and 50 would have been less than 40%. This must as a matter of logic be reflected in the percentage by which the damages are reduced…
 I am also of the view that the trial judge erred in applying the 40% reduction to all heads of damage, including those that refer only to past loss and expenses. Obviously, the damages given for past income loss and special damages would not be affected by the future contingency posited by the trial judge. As for non-pecuniary damages, since the trial judge did not consider the contingency in his initial assessment of the award of $160,000, I am of the view that this court’s comments at para. 25 of York v. Johnston (1997) 37 B.C.L.R. (3d) 235 are not applicable. There is authority for reducing damages under this head to reflect a pre-existing condition: see Zacharas v. Leys 2005 BCCA 560, at paras. 25-6. I would therefore also reduce the award for non-pecuniary damages by 20% rather than 40%.
When a Plaintiff suffers injuries by the fault of another but the evidence establishes that the person would have likely suffered the same symptoms of pain because of a pre-existing condition the Plaintiff’s award of damages can be reduced to reflect this reality. This principle of personal injury law is known as the “crumbling skull” doctrine. Reasons for judgement were released this week by the BC Supreme Court, Vernon Registry, dealing with this area of law.
In this week’s case (Booth v. Gartner) the Plaintiff was injured in a 2007 BC car crash. The Defendant struck the Plaintiff’s vehicle when he entered an intersection against a red light. ICBC admitted fault on behalf of the Defendant but disputed the extent of the accident related injuries.
At trial Mr. Justice Cole found that the accident caused a variety of injuries. One of the most significant was low back pain which continued to the time of trial. The Plaintiff did not have back pain before the car crash however she had severe pre-existing (although asymptomatic) facet arthritis in her low back. The accident caused this condition to become painful. The Court was persuaded that this condition had a likelihood of developing pain in the future even without the accident. As a result of this finding the Court reduced the Plaintiff’s non-pecuniary damages by 25%. In reaching this result Mr. Justice Cole reasoned as follows:
 I accept Dr. Vallentyne’s opinion that the degeneration in her lower back is severe at two levels and it is likely she would have been troubled by lower back pain and stiffness at some time in the future, absent Accident #2. However, I am also satisfied that although the degeneration is pre-existing, there was symptomatic acceleration of the facet arthritis as a result of Accident #2…
 The CT scan of September 20, 2008, according to Dr. Vallentyne, “showed severe bilateral degeneration of the facet joints at the L4-5-S1 levels in addition to a minor 3 mm L4-5 degenerative anterolisthesis”.
 According to Dr. Vallentyne, degenerative changes take years to develop and he found it was probable that the plaintiff had degenerative changes of her lower lumbar facet joints prior to the 2007 motor vehicle accident. He concluded that “[g]iven that the degeneration is severe at two levels, it is likely that Ms. Booth would have been troubled by low back pain and stiffness at sometime in the future absent the 2007 MVA.”
 I am satisfied that 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, and I must take that into account in reducing the overall award.
 The principle to be applied is found in Zaruk v. Simpson et al., 2003 BCSC 1748, 22 B.C.L.R. (4th) 43 [Zaruk]. There the plaintiff had suffered a soft-tissue injury but some of her symptoms by the time of trial were consistent with degenerative changes. The Court was not satisfied that the general condition would have become symptomatic between the date of the accident and the date of trial, but concluded at para. 40, that there was a measurable risk that it would have become symptomatic in the future:
 However, application of the crumbling skull doctrine may not result in the same reduction for past losses as future losses. Past losses must be assessed on the basis of a balance of probabilities. “Once the burden of proof is met, causation must be accepted as a certainty,” [Athey v. Leonati,  3 S.C.R. 458] ¶ 30). But for the assessment of future losses, “[a] future or hypothetical possibility will be taken into consideration as long as it is a real and substantial possibility and not mere speculation,” (Athey ¶ 27)
 The Court then reduced non-pecuniary damages by 15% and future care damages by 20%.
 Because the plaintiff’s degenerative condition was described by Dr. Vallentyne as “severe bilateral degeneration”, I am of the view that a large deduction is appropriate in this case and I find an appropriate deduction for non-pecuniary damages is 25% and for future care damages, 30%.
As I previously wrote, a great discussion of this area of the law was also provided in a recent case (Gohringer v. Hernandez-Lazo) where Madam Justice Russell summarized the law as follows:
 In a crumbling skull situation, as in this case, the plaintiff has a pre-existing condition which is active, or likely to become active. The pre-existing condition “does not have to be manifest or disabling at the time of the tort to be within the ambit of the crumbling skull rule”: Barnes at para. 89, citing A. (T.W.N.) v. Clarke, 2003 BCCA 670, 22 B.C.L.R. (4th) 1 at para. 62. In crumbling skull situations, the defendant is only liable for damages caused by the accident and responsible for returning the plaintiff to their original position. As Major J. stated in Athey: the defendant is liable for the additional damage but not the pre-existing damage: at para. 35. The defendant is therefore not liable for the effects of the pre-existing condition that the plaintiff would have experienced in any event: A. (T.W.N.) at para. 52. If there is a “measurable risk” that the pre-existing condition would have impacted the plaintiff in the future then, regardless of the defendant’s negligence, a court can take this into account in awarding damages: at para. 35.
 In addition, the defendant claims an independent intervening event, subsequent to the Accident, also had significant impact on the plaintiff. An independent intervening event is an unrelated event, such as disease or a non-tortious accident, that occurs after the plaintiff is injured. The impact of such events is taken into account in the same manner as pre-existing conditions: Barnes at para. 96. Thus, the plaintiff is only entitled to damages which flow from the difference between his or her original position and their “injured position”: Athey at para. 32. If the unrelated event would have impacted the plaintiff’s original position adversely, the “net loss” attributable to the accident at issue will not be as great and damages will be reduced proportionately: Barnes at para. 96.
 I note that our Court of Appeal has stated that a reduction in damages to reflect the impact of independent intervening events or pre-existing conditions applies equally to non-pecuniary and pecuniary damages: A. (T.W.N.) at paras. 36-37; Barnes at para. 90.
In BC Injury Claims (tort claims) a damage award can be reduced to account for the extent that a pre-existing condition contributes to a subsequent impairment. Reasons for judgement were released today by the BC Court of Appeal discussing this area of law in the context of a jury trial.
In today’s case (Laidlaw v. Couturier) the Plaintiff was involved in a 2004 motor vehicle accident. The Plaintiff suffered from various pre-existing difficulties including depression. He was injured in the car accident and following a Jury Trial his damages were assessed at $128,717. The Jury went on to reduce this award by 85% to take into account the “measurable risk that the plaintiff would have suffered from the (post accident) physical and psychological complaints even if the (car accident) had not happened“.
The Plaintiff appealed this jury award arguing that the trial judge made a mistake in having the Jury give a general ‘across the board’ reduction of damages for the risk of difficulties the pre-existing conditions may have posed. The BC Court of Appeal agreed that the trial judge did indeed err in instructing the Jury and ordered a new trial. In coming to this conclusion the BC high court extensively discussed the law of reduction of damages to account for risks of pre-existing conditions. The highlights of this discussion were as follows:
 Ultimately, this appeal turns on a significant error exposed in the jury charge, in the third jury question, and the ultimate verdict.
 As can be seen from the emphasized portion of the jury charge recited in paragraph 26 of these reasons, the trial judge instructed the jury that if they found that “if the May 2004 accident had not happened there was a material risk that Mr. Laidlaw would nevertheless have suffered from general anxiety or depression or back problems, then you should reduce Mr. Couturier’s liability by the amount of that material risk, whatever you find it to be.”…
 The wording of question 3, together with the judge’s charge on causation was overly simplistic. The various conditions from which the plaintiff had suffered previously, and the symptoms to which they gave rise, were not capable of reduction to a single “measurable risk”.
 One, some or none of those previous conditions might have “detrimentally affected the plaintiff in the future”. One or more of those conditions might have affected him at different points in time. The degree to which each such condition might have affected him need not have been identical.
 To lump these variables together into one question and to invite a single mathematical adjustment was unfair and inappropriate.
 Athey was a case with a single identifiable injury, a disc herniation, occurring some months after the accidents giving rise to the plaintiff’s claim. There was a single pre-existing condition, “a history of minor back problems”, which was alleged to have contributed to his injury. I do not read the language in Athey, while appropriate to the kind of case with a single measurable risk, to be transferable to the facts of a more complex case such as this one, which involves the assessment of multiple and distinct measurable risks.
 The contributing effects of a pre-existing condition to a subsequent injury can be taken into account if the trier of fact considers that to be appropriate. In many cases, it may well be a relevant factor for the jury to consider. However, the jury should be told that the effect to be given to such a “measurable risk” should be carefully related to the specific facts of the case. In a case such as this, where there were various pre-existing conditions, and where it was uncertain if, when, or to what degree those conditions might adversely affect the plaintiff in future, it was an error to invite a general reduction across the board, as is required by question 3.
 In my opinion, the first portion of the charge on causation and in question 3 directed the jury to undertake a formulaic approach to the assessment of damages attributable to the defendant rather than directing them to consider, in a nuanced fashion, all of the contingencies and risks inherent in Mr. Laidlaw’s individual circumstances and to arrive at a global assessment of damages. Question sheets such as this one that ask the jury to answer questions that tend to reveal their deliberations are not helpful, invite appeals, and are to be avoided.
 It must be said that the second portion of the trial judge’s written instructions did not mirror the wording in question 3. However, it stands to reason that by the time the jury was completing its deliberations, their focus must have been on the question sheet. Question 3 is clear in its terms but, unfortunately, incorrect in its legal effect. In my view, it amounts to misdirection…
 In the end, it is impossible to say with confidence that the jury properly understood its task in assessing the damages due to Mr. Laidlaw. In my view, the only recourse available is to order a new trial.
How is a claim for compensation affected if you suffer from pre-existing injuries and as a result of the fault of another have your injuries aggravated? If your injuries would have deteriorated eventually without the intervening event your claim for damages can be adjusted accordingly. This is sometimes referred to as the ‘crumbling skull’ principle and reasons for judgment were released today by the BC Supreme Court, New Westminster Registry, applying this point of law.
In today’s case (Jopling v. Bradowich) the Plaintiff was injured in a 2004 BC Car Crash. The Plaintiff’s accident related injuries included headaches, disturbed sleep, depression and chronic pain. However, the Plaintiff suffered from pre-existing problems which were summarized by Mr. Justice Rice as follows: “ I am satisfied that the plaintiff suffered from pre-existing injuries to her lower back prior to the motor vehicle accident, and that there was a general degeneration of her spine, all of which were likely to lead her to the condition that she now experiences, although probably not as soon as it did because of the accident.”
The Court valued the Plaintiff’s non-pecuniary loss (pain and suffering) at $75,000 but then reduced this award by 20% to ‘reflect the contingencies that her back and shoulder pain would have manifested regardless of the accident‘.
In reaching this conclusion Mr. Justice Rice made the following observations of the law of causation in BC personal injury claims:
29] The principal issue in this action is whether the plaintiff’s individual injuries were caused by the accident, or whether they were only aggravations of pre-existing injuries.
 Proof of causation is determined by the “but for” test: Athey v. Leonati,  3 S.C.R. 458, at para. 14; Hanke v. Resurfice, 2007 SCC 7,  1 S.C.R. 333, at para. 21). If I find that “but for” the defendant’s conduct the plaintiff would not have been injured, then the defendant is liable for all the damages flowing from those injuries. If the conduct of the defendant is unrelated to the alleged loss, then the defendant is not liable.
 It is no answer to a plaintiff’s claim for damages that he or she would have suffered less injury or no injury at all had he or she been less susceptible. If an individual has a pre-existing condition, the person who injures that individual must take him or her as found: Athey, at para. 34.
 However, if the plaintiff’s injuries would have manifested themselves on their own in the future regardless of the defendant’s conduct, the court must apply a contingency factor to address that possibility. Such a contingency does not have to be proven to a certainty. Rather, it should be given weight according to its relative likelihood: Athey, at para. 35.
Reasons for judgement were released yesterday by the BC Supreme Court (Pavlovic v. Shields) awarding a Plaintiff just over $134,000 in total damages as a result of injuries sustained in 2 separate motor vehicle collisions.
The first collision was in 2006 and the second in 2007. Both were rear-end crashes and the Plaintiff was faultless in both collisions. Often in ICBC Injury Claims involving multiple collisions where fault is not at issue damages are assessed on a global basis and that is what occurred in this case.
Mr. Justice Rice found that the Plaintiff had pre-existing back and shoulder pain before these accidents that that even without these accidents the Plaintiff would have continued to have pain in these areas. The Court made the following findings with respect to the Plaintiff’s injuries and awarded $40,000 for her non-pecuniary loss (pain and suffering / loss of enjoyment of life):
 In this case, the plaintiff had back and shoulder pain pre-dating both accidents. This is a “crumbling skull” situation. It is more probable than not that the plaintiff would have experienced ongoing problems with back pain, for which she had already seen a Dr. Ansel Chu on several occasions in 2003. The plaintiff claims these injuries were fully resolved, and relies on Dr. Chu’s report of August 14, 2003, in which he states that the plaintiff had had good relief from pain following a series of trigger point injections. However, Dr. Chu does not state that her injuries had resolved, merely that she was “doing quite well” and that she could make a further appointment with him if the pain flared up again. That the plaintiff made no further appointments is likely explained by the fact that she went to Europe for an extended period shortly after her last appointment with Dr. Chu.
 The evidence from Dr. Petrovic’s report is that only two permanent injuries from the accidents are likely: the TMJ and the right hip. He would defer to the experts on those and has a guarded prognosis for the remainder of her injuries. Dr. Epstein testified that the TMJ injury is likely to improve with continued treatment. Dr. Smit was of the opinion that the right hip would require surgery.
 I accept that the plaintiff had no pre-existing hip or jaw complaints and that these are her principal injuries. The hip may require surgery and her jaw will require ongoing management and treatment. The defendants are fully liable for these injuries. Her other injuries – the neck, shoulder and back pain – are likely to improve over the next year. The effects of the concussion resolved nine months after the accident. Taking these factors into account, I consider an award of $50,000 in non-pecuniary damages appropriate in the circumstances, the bulk of which reflects the injuries to the jaw and hip, discounted by 20% to reflect the plaintiff’s pre-existing chronic back pain, for a total of $40,000.
Mr. Justice Rice also did a good job explaining 2 legal principles which often arise in ICBC Injury Claims – the ‘thin-skull’ principle vs. the ‘crumbling skull’ principle. He summarized these as follows:
 The defendant does not go so far as to deny that the accident caused or contributed to the plaintiff’s injuries. The concern is as to the extent. The issue is whether this is a “thin skull” or a “crumbling skull” situation. Both address the circumstances of a pre-existing condition and its effect upon the accident victim. The law is that the defendant need not compensate the plaintiff for any debilitating effects of a pre-existing condition if the plaintiff would have experienced them regardless of the accident: Athey v. Leonati,  3 S.C.R. 458 at para. 35, 140 D.L.R. (4th) 235. The court requires “a measurable risk” or “a real or substantial possibility and not speculation” that the pre-existing condition would have manifested in the future regardless of the plaintiff’s negligence. The measurable risk need not be proven on a balance of probabilities, but given weight according to the probability of its occurrence: Athey v. Leonati, at para. 27.
 The injury is deemed “thin skull” when there is a pre-existing condition that is not active or symptomatic at the time of the accident, and that is unlikely to become active but for the accident. If the injury is proven to be of a thin skull nature, then the defendant is liable for all the plaintiff’s injuries resulting from the accident.
 A “crumbling skull” injury is also one where there is a pre-existing condition, but one which is active or likely to become active regardless of the accident. If the injury is proven to be of a crumbling skull nature, then the plaintiff is liable only to the extent that the accident caused an aggravation to the pre-existing condition.