EFFECTS OF LIDOCAINE ON NUCLEUS PULPOSUS-INDUCED NERVE ROOT INJURY - A NEUROPHYSIOLOGIC AND HISTOLOGIC-STUDY OF THE PIG CAUDA-EQUINA

Study Design. Application of autologous nucleus pulposus on nerve root s and treatment with local application of lidocaine in the pig. Object ives. Studies of the effects of lidocaine on nucleus pulposus-exposed nerve roots. Summary of Background Data. Nerve root infiltration may i mprove radicular symptoms beyond the pharmacologic duration local anes thetics, but the mechanisms for this effect are not known. Methods. Nu cleus pulposus was harvested from a lumbar disc and placed onto the sa crococcygeal cauda equina in pigs. In Series 1, early lidocaine treatm ent of nucleus pulposus-induced nerve root injury, pigs received 2% li docaine (n = 5) or saline (n = 5) before and after surgery. Nerve cond uction velocity and histologic appearance were studied after 3 days. I n Series 2, delayed lidocaine treatment of nucleus pulposus-induced ne rve root injury, after 7 days 2% lidocaine was administered epidurally to nucleus pulposus-exposed (n = 4) and -nonexposed (n = 4) nerve roo ts. Nerve conduction velocity, muscle action potentials, and histologi c appearance were assessed. Results. In Series 1, early treatment with lidocaine limited the reduction in nerve conduction velocity. The epi dural inflammation was less in lidocaine treated animals. In Series 2, nerve conduction velocity was lower in nucleus pulposus-exposed anima ls than in nonexposed animals. The initial reduction of nerve conducti on velocity and muscle action potential was similar between the groups , but the recovery of muscle action potential was slower and less comp lete in nucleus pulposus-exposed nerve roots. There was minimal histol ogic nerve injury in both series and in both protocols. Conclusions. E arly treatment with lidocaine may reduce nucleus pulposus-induced nerv e root injury. Lidocaine induced a delayed recovery in nerve roots exp osed to nucleus pulposus. Further studies are needed to clarify the th erapeutic effects of nerve root infiltration and the pathophysiology o f nucleus pulposus-induced nerve root injury.