Wage loss claims that involve a plaintiff with pre-existing injuries are always complicated. It is the courts role to determine what losses are attributable to the new claim and what losses would have occurred in any event.
http://www.courts.gov.bc.ca/jdb-txt/sc/17/20/2017BCSC2098.htm
In this recent Supreme Court of British Columbia case, the plaintiff was employed as a fisherman, with a history of working as a crew member or a skipper on seine style fishing boats. The plaintiff, at the time of their motor vehicle accident, was approximately 67 years old and had a pre-existing arthritis in his wrists and hands and diabetes. The plaintiff, after the accident, had surgeries to correct carpal tunnel syndrome, but the courts ruled that the carpal tunnel syndrome and the resulting surgeries were unrelated to the accident. The courts also ruled that the plaintiff's arthritis would have gotten worse, even if the accident had not happened.
The plaintiff suffered a variety of soft tissue - including whiplash - injuries in a motor vehicle collision. Most notably, he suffered injury to his wrists and hands. This gave the courts the difficult task of determining what damages were related to the pre-existing hand and wrist injuries and which damages were related to injuries sustained in the motor vehicle collision. The plaintiff worked for approximately 3 more years after their accident but did not work afterwards. The plaintiff's inability to work was the result of physical injuries and external market conditions, such as variations in fish runs.
The courts ruled that the plaintiff did have some impairment in his ability to work caused by their motor vehicle accident, but much of the plaintiff's ongoing and previous income loss were due to his pre-existing injuries and resulting surgeries.
This case illustrates the difficulty in proving a past or future wage loss claim, but also illustrates that having pre-existing injuries is not a complete bar to recovery.