British Columbia, Canada
The following excerpt is from Hanger v Shin, 2019 BCSC 99 (CanLII):
The defendant is only liable for the injuries caused by the accident: Athey at para. 24. The defendant need not put the plaintiff in a better position than he was in prior to the accident: Athey at para. 35. Consistent with this principle, 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”: Athey at para. 35; see also Moore v. Kyba, 2012 BCCA 361 at para. 43.