The Federal Circuit’s October decision in Arthrex has cast doubt upon numerous invalidity proceedings through its holding that the appointment of administrative patent judges (APJs) by the Patent Trial and Appeal Board (PTAB) is unconstitutional—and a recent RPX analysis indicates that hundreds of America Invents Act (AIA) reviews may be subject to rehearing as a result. Now, the debate over the merits of the decision has taken further shape in another appeal involving the same issue, Polaris Innovations Limited v. Kingston Technology (2018-1831). On January 6, the US government and both parties each filed detailed briefs answering questions from the court about the lingering constitutional questions raised by Arthrex.