Behavioral and Morphological study of intra-articular high-concentration lidocaine hydrochloride in chronic arthritis rat

Abstract

Background: Novel local anesthetic agent, lidocaine hydrochloride (lidocaine), is known to have neuro-toxic effect as well as local analgesic effect, if it is applied to the neural tissue in high concentration. Previously, we utilized neurotoxic effect of local anesthetics to osteo-arthritic knee pain patients. The administration of high concentrated lidocaine to peri-articular tenderness points of osteo-arthritic knee resulted in long term pain relief and successful recovery of activity of daily life. However, therapeutic, neurophysiological and his to-pathological effects of intra-articularly administrated high concentration of local anesthetics are still unknown. In this study, the analgesic efficacy of intra-articular injection of 10% lidocaine was investigated in an experimental monoarthritis rat model. Methods: Experimental monoarthritis rats were induced by ipsilateral ankle joint injection of complete Freund adjuvant (CFA; 0.1 ml) twice at interval of a week. After development of CFA monoarthritis, 10% lidocaine (10LD group: n=10), 1% lidocaine (1LD group: n=9) and saline (control group: n=9) were injected to affected ankle joints. Secondary hyperalgesia induced by monoarthritis was assessed with paw withdrawal reflex (PWR) testing. PWR testing was done with von-Frey filaments before and 1 - 21 days after the injection. The treated articular tissues were histologically examined after the experiments. Results: PWR continuously increased after CFA injection in all groups. Restoration of PWR to baseline was observed in three weeks after treatment in 10LD group, but not in control group. Furthermore, 10% lidocaine injection seemed to induce inflammatory histological changes in articular tissues. Conclusion: These results suggest that intra-articular injection of 10% lidocaine produced the analgesic effect on painful monoarthritis. Although high concentrated lidocaine induces degenerative changes of the articular tissue, the present results may contribute to establishing more effective treatment forpainful monoarthritis.