Maryland Code, Labor and Employment § 9-802

(1) the covered employee has a permanent impairment due to a previous accident, disease, or congenital condition that is or is likely to be a hindrance or obstacle to the employment of the covered employee;

(2) the covered employee suffers a subsequent compensable accidental personal injury, occupational disease, or compensable hernia resulting in permanent partial or permanent total disability that is substantially greater due to the combined effects of the previous impairment and the subsequent compensable event than it would have been from the subsequent compensable event alone;

(3) the combined effects of the previous impairment and the subsequent accidental personal injury, occupational disease, or compensable hernia result in a permanent disability exceeding 50% of the body as a whole; and

(4) the previous impairment, as determined by the Commission at the time of the subsequent compensable event, and the subsequent accidental personal injury, occupational disease, or compensable hernia are each compensable for at least 125 weeks.