What is the test for determining whether spondylosis was a contributory factor in a motor vehicle accident?

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.