 BURLINGTON, Mass., Sept. 02, 2021 GLOBE NEWSWIRE -- Flexion Therapeutics, Inc. Nasdaq:FLXN announced that the American Academy of Orthopaedic Surgeons AAOS included ZILRETTA triamcinolone acetonide extended-release injectable suspension in its updated evidence-based clinical practice guidelines for the management of osteoarthritis OA of the knee.1 