A federal appeals court ruling upholding a relatively rare permanent patent injunction offered guidance about how such injunctions can withstand judicial review.

Monday’s U.S. Court of Appeals for the Federal Circuit ruling in Broadcom Corp. v. Emulex Corp. affirmed Central District of California Judge James Selna’s December 2011 judgments that Emulex infringed Broadcom’s patent and that the patent would not have been obvious, and thus invalid, at the time of invention.