Effects of Lidocaine on Nucleus Pulposus-Induced Nerve Root Injury

Study Design. Application of autologous nucleus purposus on nerve roots and treatment with local application of lidocaine in the pig. Objectives. Studies of the effects of lidocaine on nucleus pulposus-exposed nerve roots. of Background Data. Nerve root infiltration may improve radicular symptoms beyond the pharmacologic duration of local anesthetics, but the mechanisms for this effect are not known. Methods. Nucieus pulposus was harvested from a lumbar disc and placed onto the sacrococcygeai cauda equina in pigs. In Series 1, early lidocaine treatment of nucleus pulposus-induced nerve root injury, pigs received 2% lidocaine (n = 5) or saline (n = 5) before and after surgery. Nerve conduction velocity and histologic appearance were studied after 3 days. In Series 2, delayed lidocaine treatment of nucleus pulposus-induced nerve root injury, after 7 days 2% lidocaine was administered epidurally to nucleus pulposus-exposed (n = 4) and -nonexposed (n = 4) nerve roots. Nerve conduction velocity, muscle action potentials, and histologic appearance were assessed. Results. In Series 1, early treatment with lidocaine limited the reduction in nerve conduction velocity. The epidural inflammation was less in lidocaine treated animals. In Series 2, nerve conduction velocity was lower in nucleus pulposus-exposed animals than in nonex-posed animals, The initial reduction of nerve conduction velocity and muscle action potential was similar between the groups, but the recovery of muscle action potential was slower and less complete in nucleus pulposus-exposed nerve roots. There was minimal histologic nerve injury in both series and in both protocois. Conclusions. Early treatment with lidocaine may reduce nucleus pulposus-induced nerve root injury. Lidocaine induced a delayed recovery in nerve roots exposed to nucleus pulposus. Further studies are needed to clarify the therapeutic effects of nerve root infiltration and the pathophysiology of nucleus pulposus-induced nerve root injury.