A fund associated with the activist hedge fund Jana Partners has bought an undisclosed stake in Zimmer Biomet, according to a federal merger filing. That occurred just one day after Zimmer, a medical device conglomerate, nudged out CEO David Dvorak due to another dismal quarter by Wall Street's standards.

Why it matters: Jana is known to shake things up, and Zimmer has already started down that path. Amazon acquired Whole Foods after Jana bought its stake, and the hedge fund was around when Time changed top leadership. Jana is also somewhat familiar with medical devices, owning part of NuVasive. Jana and Zimmer did not immediately respond to questions.