Thin skull rule (also called the egg shell skull rule)

According to the thin skull rule, claimants are entitled to compensation if they suffer an injury even if such injury would not have been suffered by an average person in the same circumstances. This is because the law considers it proper that a tortfeasor must “take his victim as he finds him” and the fact that some people are more susceptible to injury than average should not be held against them.
The name of the rule comes from the idea that if a person with an abnormally thin or fragile skull (an “egg shell skull”) suffers an injury when bumped on the head with such force that would not injure an average person, he or she should nevertheless receive compensation.
Cases have confirmed that the tortfeasor is required to take his victim as he finds him and compensate for all injuries suffered by the victim, regardless of whether a less fragile victim would have suffered the same injuries:
The law is clear that the wrongdoer must take his victim as he finds him. I cite in support of this Marconato and Marconato v. Franklin, [1974] 6 W.W.R. 676 at p. 690. There Aikins, J.A. relied on the celebrated passage in the decision of Kennedy, J. is Dulieu v. White & Sons, [1901] 2 K.B. 669 at 679, which passage propagated the line of so-called “thin skull” cases, and where he said:
‘If a man is negligently run over or otherwise negligently injured in his body, it is no answer to the sufferer’s claim for damages that he would have suffered less injury, or no injury at all, if he had not had an unusually thin skull or an unusually weak heart.’
(Pryor v. Bains (1986), 1986 CanLII 161 (BCCA)).
It was apparent from Ms. Randhawa’s testimony and from her medical history, in particular her psychological history, that she does not deal well with the challenges posed by pain and physical limitations.  She tends to fixate on her pain and problems.  This was described by various experts as “pain syndrome” or “pain behaviour”. In any event, this too falls within the thin skull rule. The plaintiff was emotionally and physically fragile at the time of the accident, and the defendant must take the plaintiff as he finds her.
(Randhawa v. Hwang, 2008 BCSC 435 at para. 43).
Generally, the thin skull rule is a rule of causation and if the plaintiff had no pre-existing conditions, but only a latent weakness, the tortfeasors will be liable for the full loss:
In a case where a second source or cause of damages is found to aggravate an existing and active first source or cause, that is a case of aggravated damages and there may be an apportionment of damages as between the two sources or causes. On the other hand, in a case where a second source or cause of damages triggers the first source or cause which has been found immediately prior to the injury to be merely a latent weakness or susceptibility am not an active source or cause, that is a “thin skull” case and there can be no apportionment as between the two sources or causes and full damages must be awarded against the tortfeasor creating the second source or cause of damages which triggered the latent first source or cause.
(Pryor v. Bains, 1986 CanLII 161 (BCCA)).
In Pryor v. Bains, 1986 CanLII 161 (BCCA), which was found to not be a thin skull case, the plaintiff suffered chronic pain before and after the accident:
I do not consider this to be a case for the application of the “thin skull’ principle of assessing damages. The present case, where there was a pre-existing condition, as found by the trial judge, already manifest and presently disabling, must be distinguished from the “thin skull” cases where the weakness or latent susceptibility of the victim is quiescent but is activated into being as a result of the tortuous conduct of another.
(Pryor v. Bains (1986), 69 BCLR 395 (C.A.))
The fact that the part of her body the plaintiff was psychologically fixated on changed did not make it a thin skull case:  
I have not been persuaded that the trial judge misconstrued the evidence that the appellant was, at the time of the accident, using the pain of her neck injury as a psychological crutch and, following the accident, transferred the psychological crutch to the pain in the lumbar area of the back. This is a matter of fact. That being so, I must find that the trial judge correctly treated this as a case of aggravated damages rather than a “thin skull” case.
(Pryor v. Bains, 1986 CanLII 161 (BCCA)).
That a plaintiff who is symptomatic at the time of the accident is not truly a thin skull plaintiff was confirmed in Larwill v. Lanham, 2003 BCCA 629:
A non-tortious cause that precedes the accident but contributes to the injury, referred to as a precondition by Major J., is not relevant to causation [thin skull] unless it is symptomatic at the time of the accident [aggravation], when Pryor v. Bains (1986), 69 BCLR (3d) 395 (C.A.), will apply and the damages will be confined to the aggravation caused by the accident to the symptomatic condition. 
(Larwill v. Lanham, 2003 BCCA 629 at para. 22).
Other cases have confirmed that where there are pre-existing symptoms defendants are only liable to compensate the claimant for the exacerbation caused by the accident:
[T]his was a "thin skull" case — i.e., a case in which it was not appropriate to apportion liability as between the plaintiff and defendants as between two or more defendants, or as between two or more causes.  The defendants must be held responsible for all the damages that flow, not from Ms. York's disease as a whole, but from the exacerbation thereof.  I also consider that the trial judge was entitled to reduce the plaintiff's damages to reflect the risk of relapse that was inherent in her pre-accident state
(York v. Johnston, 1997 CanLII 4043 at para. 7 (BCCA)).
A further aspect of the thin skull rule is that a plaintiff’s fragile state may be relevant to quantifying the effect of the defendant’s wrong act. In Blackwater v. Plint, 2005 SCC 58 the plaintiff was fragile because of previous trauma, and then suffered sexual assault at the Alberni Indian Residential School (“AIRS”). The Supreme Court of Canada held that the plaintiff’s fragile pre-existing state was relevant to the assessment of damages:
[T]he defendant takes his victim as he finds him — the thin skull rule.  Here the victim suffered trauma before coming to AIRS.  The question then becomes: What was the effect of the sexual assault on him, in his already damaged condition?  The damages are damages caused by the sexual assaults, not the prior condition.  However, it is necessary to consider the prior condition to determine what loss was caused by the assaults.  Therefore, to the extent that the evidence shows that the effect of the sexual assaults would have been greater because of his pre-existing injury, that pre-existing condition can be taken into account in assessing damages.
(Blackwater v. Plint, 2005 SCC 58 at para. 79).
The foregoing indicates that if a claimant is fragile, but not symptomatic, before the accident, he or she will likely be entitled to compensation for all symptoms caused by the accident. However, if the claimant is symptomatic before the accident he or she will only be compensated for the exacerbation in symptoms caused by the accident.


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