In Morrison v. Alaska Interstate Construction Inc., the supreme court held that the substantial cause test under the 2005 amendments to the Alaska Workers’ Compensation Act requires the Alaska Workers’ Compensation Board to compare the causes of the need for medical treatment and decide compensation issues based on the most important or material cause. Morrison injured his knee at work for SKW Eskimos, Inc. in 2004, and he returned to work without issue for the next ten years. In 2014, while working for Alaska Interstate Construction, Inc., Morrison again injured his knee at work. When Alaska Interstate Construction contested its liability for medical care, the Alaska Workers’ Compensation Board ruled the 2014 work injury was the substantial cause of Morrison’s current need for medical care, so Alaska Interstate Construction— not SKW Eskimos—was responsible for continued care. On appeal, Alaska Interstate Construction argued the Board failed to adequately consider the extent to which the 2014 injury contributed to the need for medical care following the 2014 injury. Affirming the Board’s interpretation of the causation requirement, the supreme court held that the Board must identify one cause as the substantial cause. The supreme court reasoned, based on legislative history, that the 2005 amendments narrowed the compensability standard for workers’ compensation benefits by replacing the substantial factors test with the substantial cause test. In determining which cause was substantial, the Board retained flexibility because all its determinations were fact-dependent. Affirming the Board’s weighing of the relevant causes and ruling that the 2014 work injury was the substantial cause, the supreme court held the Board properly decided the compensation issue based on the most important or material cause.
 440 P.3d 224 (Alaska 2019).