Effects of Premixing Betamethasone and Lidocaine on Chondrocyte Inflammation in an In Vitro Model

Background: It is common practice for hand surgeons to premix corticosteroids with a local anesthetic and store the mixture in pre-loaded syringes for rapid use during clinic. However, any possible loss of efficacy with this practice has never been studied. The purpose of this study, therefore, is to determine whether premixing betamethasone sodium phosphate/betamethasone acetate (BSP) and lidocaine (L) at different time intervals from injection has diminishing anti-inflammatory effects on chondrocytes in vitro. Methods: Human articular chondrocytes were partitioned into six groups: two controls and four experimental conditions. The negative control had growth media only. The positive control had growth media and inflammatory cytokines (interleukin-1β and oncostatin M). Experimental conditions were additionally treated with BSP alone or BSP mixed with lidocaine (BSP + L) at the time of treatment (0 hours), or at 4 or 24 hours prior. Relative expressions of inflammatory genes were measured. Results: Relative to the positive control, chondrocytes in all experimental conditions decreased expression of TNF-α, MMP-3, and ADAMTS-4. Chondrocytes exposed to BSP only or BSP + L at 4 hours or 24 hours prior to treatment decreased expression of IL-8. Chondrocytes exposed to BSP only or BSP + L at 0 hours or 4 hours prior to treatment decreased expression of MMP-1. There were no significant differences in expression of IL-6 or MMP-13. Conclusions: Treatment with BSP + L prepared in pre-loaded syringes at varying time intervals up to 24 hours prior to injection does not significantly impact the ability of the mixture to reduce expression of certain key inflammatory mediators in vitro.