“Preexisting conditions” is an excuse that the insurance companies like to use to deny benefits. Frequently they will hire their own doctor ("IME") to say that an Employee’s need for medical treatment or his disability is not because the Employee was injured at work, but instead due to preexisting conditions, usually degenerative disc disease.
The law is clear: work-related injuries which aggravate, accelerate or combine with pre-existing conditions to cause a disability or need for medical treatment is still a Workers Compensation injury.