I had an interesting case today where the insurance carrier's doctor is saying that my client's need for a total knee replacement is not related to his 1985 industrial injury because he had a prior non-industrial injury in 1974. His argument is that, since there were already degenerative changes in the knee at the time of the 1985 injury, he would have needed the total knee eventually regardless of whether he had the industrial injury.
This is actually a very common issue in Arizona Workers (Workmans) Compensation claims - where a worker has a pre-existing non-industrial degenerative condition that is aggravated or exacerbated by an industrial injury. It is generally accepted that, if the subsequent work injury causes a permanent aggravation of the underlying condition, or speeds up the need for care for the degenerative condition, it is the workers comp carrier's responsibility. Although there is not a specific test for this, the industrial injury has to be at least a "substantial contributing factor" in adding to the need for the treatment - "substantial", however, is ill defined and can mean at least a minimal factor in causing the need for the treatment.
Bottom line: a pre-existing condition can either be temporarily aggravated or permanently aggravated by an on the job injury and be covered under workers compensation. This usually has to be established by medical testimony from your doctor.
Chad T. Snow is a workers compensation attorney with offices in Phoenix and Tucson. He has represented thousands of Arizona's injured workers before the Industrial Commission of Arizona. He can be reached at (602) 532-0700 or (520) 647-9000 or on his website at http://www.snowcarpio.com/.