Michael Karr, a college student in Las Vegas, hoped to make some side income from a raunchy iPhone app called “69 Positions.” What Karr didn’t foresee was that the app would drag him into costly patent litigation with Lodsys Group, a prolific patent assertion entity (or “patent troll”). Kare settled last October, lamenting at the time in an email to Paidcontent.org that a judge hadn’t yet ruled on a June 2011 motion by Apple Inc. to intervene on his behalf and on behalf of other app developers sued by Lodsys. Last week, the app developers who are still fighting — including Rovio, the maker of the wildly popular smartphone game “Angry Birds” — finally got the ruling Karr had wanted.

In a long-awaited opinion issued on Thursday, Judge Rodney Gilstrap of the U.S. District Court for the Eastern District of Texas granted Apple’s motion to intervene. As Litigation Daily previously reported, Apple’s lawyers at Simpson Thacher & Bartlett argued that the app developers are protected by Apple’s license to the Lodsys patents. Lodsys disputes that the license, which Apple signed with the patents’ previous owner (the patent aggregator Intellectual Ventures), extends to the app makers.