Nova Scotia appeal court orders fresh review of worker’s knee claim

The Nova Scotia Court of Appeal has sent a worker’s compensation claim back to the appeal tribunal, ruling that a finding her later knee problems were related “at least in part” to an earlier workplace injury did not establish the required causal connection.

In Nova Scotia (Workers’ Compensation Board) v. O’Brien, 2026 NSCA 73, released October 14, 2026, the court allowed the Workers’ Compensation Board’s appeal without costs. The tribunal must decide causation again using the proper legal test. The court did not itself finally decide whether the later symptoms qualify for compensation.

Justice Farrar, writing for Chief Justice Wood and Justice Derrick as well, also said the material-contribution test should no longer be used to determine causation in the workers’ compensation context. The reasons instead point to the legislation’s benefit-of-the-doubt rule when the ordinary causal test is unworkable.

Dispute concerned later symptoms, not the original accident

Patricia O’Brien was working as a continuing care assistant when she slipped and fell at work in September 2015. The board accepted the resulting knee strain as a compensable injury. She received physiotherapy and was discharged from treatment that November.

In 2019, she reported continuing knee pain that had worsened. The dispute was whether those symptoms were connected to the accepted workplace injury or to other degenerative changes.

The board rejected the claimed connection, and a hearing officer upheld that decision. In 2022, the Workers’ Compensation Appeals Tribunal returned the matter to the board for updated medical information rather than deciding the merits on evidence it considered too speculative.

After further medical investigations, the board and a hearing officer again rejected the connection. On a second appeal to the tribunal, O’Brien relied on a specialist’s report concluding that the 2015 injury had contributed at least partially to her later problems. The tribunal preferred that opinion to those of the board’s medical advisers and allowed her appeal in September 2025.

A merely trivial connection was not enough

The board obtained leave to appeal on a narrow legal question: whether the tribunal had applied an unlawful causation test. The court reviewed that question for correctness, rather than deferring to the tribunal’s legal interpretation.

The tribunal had initially stated the ordinary “but for” test: would the later problems have occurred without the workplace injury? It had also correctly recognized that the compensable injury did not have to be the sole cause.

But when applying the test to the medical evidence, the tribunal accepted a connection “at least in part.” The Court of Appeal held that this formulation could allow any relationship, however trivial, to establish a compensable claim. The required connection must be more than negligible.

The court distinguished an earlier decision that had accepted similar language. That case involved a different standard of review, an employer’s argument that work had to be the sole cause, and no suggested source of symptoms outside employment. It did not support treating every partial connection as sufficient.

Statutory benefit of the doubt remains available

The court went on to address the use of material contribution, although the board had not challenged that test in its appeal. The issue had been raised with counsel during oral argument.

Drawing on the Supreme Court of Canada’s explanation of material contribution to risk in negligence law, Justice Farrar said it should not be treated as a causation test in this no-fault compensation system.

Section 187 of Nova Scotia’s Workers’ Compensation Act provides its own protection for applicants: when there is doubt about an issue and the competing possibilities are evenly balanced, the issue must be resolved in the worker’s favour. The court said that, if the “but for” test is unworkable, the causation inquiry becomes whether the connection is as likely as not.

The tribunal must now reassess the claim on that basis. The decision changes neither the accepted status of the original 2015 injury nor the requirement that an employment-related injury need not be the only cause of a later condition.