Maryland Labor and Employment Section 9-656

      (a)      If it appears that a permanent disability of a covered employee following an accidental personal injury or occupational disease is due partly to the accidental personal injury or occupational disease and partly to a preexisting disease or infirmity, the Commission shall determine:

            (1)      the proportion of the disability that is reasonably attributable to the accidental personal injury or occupational disease; and

            (2)      the proportion of the disability that is reasonably attributable to the preexisting disease or infirmity.

      (b)      The covered employee:

            (1)      is entitled to compensation for the portion of the disability of the covered employee that is reasonably attributable solely to the accidental personal injury or occupational disease; and

            (2)      is not entitled to compensation for the portion of the disability that is reasonably attributable to the preexisting disease or infirmity.