77 Pa. Stat. § 871
The board, upon petition of any party and upon cause shown, may grant a rehearing of any petition upon which the board has made an award or disallowance of compensation or other order or ruling, or upon which the board has sustained or reversed any action of a referee; but such rehearing shall not be granted more than eighteen months after the board has made such award, disallowance, or other order or ruling, or has sustained or reversed any action of the referee. Provided, however, That nothing contained in this section shall limit or restrict the right of the board, or a referee to review, modify, set aside, reinstate, suspend, or terminate, an original or supplemental agreement, or an award in accordance with the provisions of section four hundred thirteen of this article.
77 P.S. § 871