Effects of lidocaine on blood flow and endoneurial fluid pressure in a rat model of herniated nucleus pulposus.

Study Design: An experimental study was conducted to evaluate the effects of lidocaine on nucleus pulposus-induced pathophysiologic changes.
Objectives: To investigate the effects of lidocaine on blood flow in the hind paws and endoneurial fluid pressure in the dorsal root ganglia in a rat model of herniated nucleus pulposus, and to clarify the therapeutic mechanisms of nerve root infiltration.
Summary of Background Data: It has been shown experimentally that application of nucleus pulposus to the nerve roots increases endoneurial fluid pressure and decreases blood flow in the dorsal root ganglia and the corresponding hind paw. These changes are thought to be an important pathogenic mechanism associated with sciatica caused by disc herniation. Nerve root infiltration is one of the nonoperative effective therapies for radiculopathy caused by disc herniation. However, the therapeutic mechanisms still are unknown.
Methods: For this study, 21 Sprague-Dawley rats were used. Autologous nucleus pulposus was applied to the nerve root with a piece of Spongel containing lidocaine (lido group) or physiologic saline solution (control group). In Series 1 of this study (Blood Flow in the Hind Paw), blood flow in the corresponding hind paws was monitored continuously using a laser Doppler flowmeter before application of the test solutions, and every 5 minutes thereafter for an additional 3 hours in both the control (n = 5) and lido (n = 5) groups. In Series 2 of this study (Endoneurial Fluid Pressure in the Dorsal Root Ganglion), endoneurial fluid pressure was recorded with a servo-null micropipette system using glass micropipettes before and 3 hours after application of the test solutions in both the control (n = 6) and lido (n = 5) groups. After measurements, dorsal root ganglia were assessed for histology.
Results: In Series 1, blood flow in the corresponding hind paw in the control group showed significant reduction as compared with that of the Lido group, starting about 90 minutes after application (P < 0.01-0.05). Hind paw blood flow in the lido group did not show any reduction during measurements. In Series 2, the value of endoneurial fluid pressure in the lido group 3 hours after application was significantly lower than in the control group (P < 0.01). Interstitial (endoneurial) edema in the dorsal root ganglion in the lido group appeared to be qualitatively less than in the control group.
Conclusions: The data indicate that lidocaine reduces the pathophysiologic changes in the dorsal root ganglion and hind paws induced by nucleus pulposus. These effects of lidocaine may relate to the mechanisms underlying the therapeutic effects of nerve root infiltration.