Combined spinal cord monitoring using neurogenic mixed evoked potentials and collision techniques.
METHODS
Neurogenic mixed evoked potentials are used routinely to monitor the spinal cord during spine surgery. This study investigates the differential sensory-motor contribution by using collision techniques.


OBJECTIVE
To demonstrate that neurogenic mixed evoked potentials do contain a motor component.


BACKGROUND
Spinal cord monitoring is now routinely used during spine deformity surgery. Neurogenic mixed evoked potentials (i.e., potentials recorded from lower limb nerves after spinal cord stimulation) represent a reliable and sensitive technique. However, their specificity (sensory and motor spinal pathways) remains debated.


METHODS
Neurogenic mixed evoked potentials and collisions were performed in 24 consecutive patients during scoliosis surgery. Neurogenic mixed evoked potentials were elicited by a high thoracic spinal test stimulation and recorded from the tibial nerve at the ankle. A peripheral conditioning stimulation was delivered at the popliteal fossa 15 ms before spinal stimulation, inducing an ascending volley. The antidromic ascending motor component stops at the anterior horn cell level, whereas the orthodromic sensory component reaches the dorsal columns. The 15-ms interstimulus interval between peripheral conditioning and spinal test stimulation makes the collision with descending volleys occur in the spinal cord. The descending sensory volley is blocked, whereas the descending motor volley is unaffected.


RESULTS
Reproducible evoked potentials were recorded from the tibial nerve in all the patients studied when the conditioning stimulation was performed. These conditioned neurogenic mixed evoked potentials consist of a small and polyphasic wave whose amplitude represents approximately 26% that of the wave of unconditioned neurogenic mixed evoked potentials. It is likely that they correspond to motor spinal pathway activation.


CONCLUSIONS
Both standard and conditioned neurogenic mixed evoked potentials are proposed to provide combined sensory and motor spinal pathway monitoring.
Laboratoire d'Explorations Fonctionnelles, Hôtel-Dieu, F-44093 Nantes Cedex, France. Yann.Pereon@nantes.inserm.fr
Yann
Y
Péréon
Sylvie
S
Nguyen The Tich
Joël
J
Delécrin
Charles
C
Pham Dang
Joël
J
Bodin
Jean-Christophe
JC
Drouet
Norbert
N
Passuti
D000293:Adolescent; D000328:Adult; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D009046:Motor Neurons / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology; D012600:Scoliosis / Q000503:physiopathology / Q000601:surgery*; D013116:Spinal Cord / Q000503:physiopathology*