Legally, you may indeed collect compensation (e.g. medical costs; pain and suffering; lost wages and/or diminution of earning potential) for a pre-exisiting condition for--and only to--the extent the accident made it worse. Practically, it can be very difficult to prove the impact of the accident and separate that out from the pre-exisiting condition. You should consult with experienced personal injury counsel about this situation, to evaluate the strength of your claim and what it might be worth.