PORTLAND, Maine—The Maine Supreme Court ruled Tuesday that an injured worker cannot combine impairment ratings for accidents that he suffered, limiting the number of weeks that he can collect workers compensation benefits for some of his injuries.

The plaintiff in William Buckley vs. S.D. Warren Co. et al. sought cumulative impairment ratings for four separate injuries to his shoulders.

Under Maine workers comp law, Mr. Buckley would be allowed to receive benefits for the duration of each injury if he received a permanent impairment rating of more than 13.4%. An impairment rating under that threshold would restrict his benefits to 520 weeks for each claim.

In a 5-2 decision Tuesday, Maine's high court said that Mr. Buckley's impairment ratings should be combined for his left shoulder, resulting in “duration-of-disability” benefits injuries to that arm. However, it held that impairment ratings should not be “stacked” for a right shoulder injury, because it occurred after his left arm injuries.

Mr. Buckley was injured while working for coated paper manufacturer S.D. Warren from 1981 to 2002, court records show. The accidents included two injuries to his left shoulder in 1996, an injury to his right shoulder in 2000 and an injury to both of his shoulders in 2001.

The accidents were ruled compensable during a workers comp hearing in 2005, which excluded the 2000 injury, and another in 2008, which awarded benefits for the 2000 accident. The right shoulder injury in 2000 was deemed to be caused by Mr. Buckley's prior injuries, since he favored his left arm after the 1996 accidents.

In the 2008 decision, a workers comp hearing officer found that Mr. Buckley suffered 7% impairment in his left shoulder and 7% impairment in his right shoulder. The officer did not stack impairment ratings in that decision, partly because he found that the 2000 accident did not cause any additional injuries to Mr. Buckley's left shoulder.

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The decision was vacated in 2010 by the Maine Supreme Court. The ruling said that Mr. Buckley's impairment rates could potentially be stacked and cross the threshold for “duration-of-disability” benefits, since the injuries in each shoulder were "not unrelated," records show. The case was remanded to the workers comp hearing officer.

In a rehearing, the officer assigned a 14% total impairment rating for each of Mr. Buckley's left shoulder injuries in 1996. That decision was based on a 7% impairment rating for each left shoulder injury, plus a 7% impairment rating for Mr. Buckley’s 2000 right shoulder injury that resulted from the earlier accidents.

The officer assigned a 0% impairment rating for the 2001 accident, because it did not “aggravate or accelerate” Mr. Buckley’s earlier injuries.

However, he did not stack impairment ratings for Mr. Buckley’s right shoulder. That decision, which limited benefit weeks for the right shoulder injury, said stacking didn’t apply because “the 1996 injuries caused the 2000 injury, and not the other way around.”

The state Supreme Court upheld that decision in Tuesday's ruling. In its majority opinion, the court said its mandate in the 2010 Buckley decision allowed only for stacking of later injuries caused by earlier injuries.

In his dissent, Judge Joseph Jabar disagreed with the hearing officer’s calculations. He said Mr. Buckley’s case includes related injuries that should be combined, regardless of the timeline.

“We definitively said that permanent impairment to both shoulders should be combined when deciding whether the threshold has been reached,” said Judge Jabar, referring to the high court’s 2010 decision.