This is based on what has commonly been termed the “eggshell plaintiff rule.” The employee need not be in perfect health when he/she is hired. The employer takes the employee as he finds him – an aggravation of a preexisting condition is compensable.
What typically happens in this claims, is the attorney for the Employer/Insurer sends the Employee to one of their doctors who opines that the Employee had a temporary aggravation, but has now returned to baseline condition, thus no longer entitled to medical or wage benefits.
I, as the Employee attorney, argue and develop medical testimony to show that Employee was able to work his/her regular duty job prior to this work-related injury, but is now unable to, so hence still suffers from the aggravation.
These cases are very fact-specific and often have conflicting medical testimony. The Board has broad jurisdiction to determine whether the employee still suffers from the aggravation and if there is entitlement to medical/indemnity benefits.