Frequently a worker will have a pre-existing health condition. The pre-existing condition can be the result of numerous causes, including but not limited to the natural aging process, a prior work injury, or an accident unrelated to work.
Sometimes a pre-existing condition will make the worker more susceptible to a work injury. For example, a worker that has had prior shoulder or back surgery might be injured doing a job that would not have hurt a worker who did not have a pre-existing problem. The worker with the pre-existing condition is sometimes called an "eggshell plaintiff" because they are more easily injured than an average person. However, under Iowa work comp law even though a worker might be an eggshell plaintiff, if he gets hurt on the job he is entitled to receive workers' compensation benefits.
Sometimes a worker may have a pre-existing condition that is completely latent or symptom free and does not cause him any problems. If a worker with such an asymptomatic condition is injured on the job he will generally be entitled to be compensated for the entire resulting disability from the injury even though the final disability is caused by a combination of the pre-existing condition and the work injury.
Other times a worker may have limitations or problems because of the pre-existing condition. If this worker is injured on the job he is generally only entitled to be compensated for the increase in his disability caused by the work injury.
An important Iowa work comp rule is that in order for an injured worker with an aggravation of a pre-existing condition to be eligible to receive permanent partial disability (PPD) benefits the aggravation must be permanent, material and substantial.
A frequent dispute in aggravation cases is whether or not the worker returned to the baseline level of impairment he had before the injury. If the condition does return to the baseline level the worker will only be entitled to receive temporary total disability (TTD) benefits. If the condition does not return to the baseline level the worker will be entitled to receive both TTD and PPD benefits.
An injured worker's own testimony on the issue of whether or not the condition returned to baseline is important. However, the opinions of the treating physicians and the Independent Medical Examiner (IME) doctors frequently end up deciding this type of controversy.
The most frequent dispute in aggravation cases is probably whether the worker's job actually aggravated the pre-existing problem, or is the worsening of the condition simply because of the natural progression of the problem. This is another area where the opinions of the treating physicians and the IME doctors usually end up being the deciding factor.