Pennsylvania adopted the impairment rating provisions described in the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides) in 1996 as an exposure cap for employers seeking predictability and cost control in workers’ compensation claims. In 2017, the Supreme Court of Pennsylvania handed down the Protz decision, which held that requiring physicians to apply the methodology set forth in the most recent edition of the AMA Guides reflected an unconstitutional delegation of legislative power to the American Medical Association. The decision eliminates the impairment-rating evaluation (IRE) mechanism under which claimants were assigned an impairment rating under the most recent edition of the AMA Guides. The AMA Guides periodically are revised to include the most recent scientific evidence regarding impairment ratings, and the AMA Guides, Sixth Edition, acknowledges that impairment is a complex concept that is not yet defined in a way that readily permits an evidence-based definition of assessment. The AMA Guides should not be considered standards frozen in time simply to withstand future scrutiny by the courts; instead, workers’ compensation acts could state that when a new edition of the AMA Guides is published, the legislature shall review and consider adopting the new edition. It appears unlikely that the Protz decision will be followed in other jurisdictions: Challenges to using the AMA Guides in assessing workers’ compensation claims have been attempted in three states, and all attempts failed.