What is the thin skull doctrine and crumbling skull doctrine?

In Athey v. Leonati, Major, J., explains the difference between the thin skull and crumbling skull doctrines. He commented that where there was a measurable risk a plaintiff's pre-existing condition would detrimentally affect the plaintiff in the future regardless of the defendant's negligence, the damage award would be reduced accordingly - the crumbling skull doctrine. In our case I have arrived at the conclusion the preexisting condition, the degenerative spine condition, did not constitute a measurable risk for the future. The relevancy of the pre-existing condition was never a serious consideration at trial and was presumed so inconsequential the trial judge was able to find the appellant had "no degenerative disc disease" at all. No doubt the slip and fall accident aggravated the appellant's back condition at the time, but there was no medical evidence the slip and fall accident, separate and distinct from the pre-existing degenerative condition in her lower back, was a factor in the chronic pain syndrome or was likely, on its own, to have caused such types of pain in the future. The evidence of the expert witnesses establishes the vehicle collision caused the neck injury; there was no evidence to show there was a measurable risk the degenerative condition would eventually produce a chronic pain syndrome. The chronic pain syndrome was the consequence of the motor vehicle collision and in the absence of a measurable risk from the pre-existing condition there are no grounds to reduce the award.

There being no determination a measurable risk existed that the pre-existing degenerative back condition would progress to the stage of a chronic pain syndrome, the matter is resolved by simple application of the thin skull rule, As already stated, the pre-existing back condition may have been aggravated by the slip and fall accident, but the respondents must take the appellant as they find her. Athey v. Leonati stands for the position that if the respondent's negligence exacerbated the existing condition and caused it to manifest into a chronic pain syndrome, then the respondents are the cause of the chronic pain syndrome and therefore fully liable. I am still of the view however, that the medical evidence of the expert witnesses does not establish the slip and fall accident is in any way a contributory cause of the chronic pain syndrome.