Pacira Biosciences Inc. will add to its core non-opioid-based therapies business by buying Flexion Therapeutics Inc. for $427 million. That brings into the company’s fold Zilretta (triamcinolone acetonide extended-release injectable suspension) for treating osteoarthritis knee pain, an injectable non-opioid that’s already FDA approved in addition to being in a phase II study for treating shoulder osteoarthritis.