Extreme Postinjection Flare in Response to Intra-Articular Triamcinolone Acetonide (Kenalog).

As intra-articular corticosteroid injections (CSIs) are a common treatment for osteoarthritis, physicians must well understand their potential side effects. Postinjection flares are an acute side effect of intra-articular CSIs, with symptoms ranging from mild joint effusion to disabling pain. The present case involved a severe postinjection flare that occurred after the patient, a 56-year-old woman with moderate osteoarthritis in the left knee, received 2 mL of 1% lidocaine and 2 mL (40 mg) of triamcinolone acetonide (Kenalog). Two hours after injection, she experienced swelling and intense pain in the knee and was unable to ambulate. The knee was aspirated with a return of 25 mL of "butterscotch"-colored fluid. This case is novel in that its acuity of onset, severity of symptoms, and synovial fluid analysis mimicked septic arthritis, which was ultimately ruled out with negative cultures and confirmation of triamcinolone acetonide crystals in the synovial aspirate, viewed by polarized light microscopy. Thus, the patient's reaction represents an acute crystal-induced inflammatory response. Although reactions to an intra-articular CSI of this severity are rare, it is important for treating physicians to inform patients of this potential side effect.