The Journal of Bone and Joint Surgery (American) 86:1248-1253 (2004)
© 2004 The Journal of Bone and Joint Surgery, Inc.
Comparison of Transcranial Electric Motor and Somatosensory Evoked Potential Monitoring During Cervical Spine Surgery
Alan S. Hilibrand, MD1,
Daniel M. Schwartz, PhD, DABNM2,
Venkat Sethuraman, MD1,
Alexander R. Vaccaro, MD1 and
Todd J. Albert, MD1
1 The Rothman Institute, 925 Chestnut Street, 5th Floor, Philadelphia, PA
19107
2 Surgical Monitoring Associates, 25 Bala Avenue, Suite 105, Bala Cynwyd, PA
19004. E-mail address:
danielmschwartz{at}mac.com
Investigation performed at Surgical Monitoring Associates, Bala Cynwyd,
and The Rothman Institute, Philadelphia, Pennsylvania
The authors did not receive grants or outside funding in support of their
research or preparation of this manuscript. They did not receive payments or
other benefits or a commitment or agreement to provide such benefits from a
commercial entity. No commercial entity paid or directed, or agreed to pay or
direct, any benefits to any research fund, foundation, educational
institution, or other charitable or nonprofit organization with which the
authors are affiliated or associated.
Background: There has been little enthusiasm for somatosensory
evoked potential monitoring in cervical spine surgery as a result, in part, of
the increased risk of motor tract injury at this level, to which somatosensory
monitoring may be insensitive. Transcranial electric motor evoked potential
monitoring allows assessment of the motor tracts; therefore, we compared
transcranial electric motor evoked potential and somatosensory evoked
potential monitoring during cervical spine surgery to determine the temporal
relationship between the changes in the potentials demonstrated by each type
of monitoring and neurological sequelae and to identify patient-related and
surgical factors associated with intraoperative neurophysiological
changes.
Methods: Somatosensory evoked potential and transcranial electric
motor evoked potential data recorded for 427 patients undergoing anterior or
posterior cervical spine surgery between January 1999 and March 2001 were
analyzed. All patients who showed substantial (at least 60%) or complete
unilateral or bilateral amplitude loss, for at least ten minutes, during the
transcranial electric motor evoked potential and/or somatosensory evoked
potential monitoring were identified.
Results: Twelve of the 427 patients demonstrated substantial or
complete loss of amplitude of the transcranial electric motor evoked
potentials. Ten of those patients had complete reversal of the loss following
prompt intraoperative intervention, whereas two awoke with a new motor
deficit. Somatosensory evoked potential monitoring failed to identify any
change in one of the two patients, and the change in the somatosensory evoked
potentials lagged behind the change in the transcranial electric motor evoked
potentials by thirty-three minutes in the other. No patient showed loss of
amplitude of the somatosensory evoked potentials in the absence of changes in
the transcranial electric motor evoked potentials. Transcranial electric motor
evoked potential monitoring was 100% sensitive and 100% specific, whereas
somatosensory evoked potential monitoring was only 25% sensitive; it was,
however, 100% specific.
Conclusions: Transcranial electric motor evoked potential monitoring
appears to be superior to conventional somatosensory evoked potential
monitoring for identifying evolving motor tract injury during cervical spine
surgery. Surgeons should strongly consider using this modality when operating
on patients with cervical spondylotic myelopathy in general and on those with
ossification of the posterior longitudinal ligament in particular.
Level of Evidence: Diagnostic study, Level I-1 (testing
of previously developed diagnostic criteria in series of consecutive patients
[with universally applied reference "gold" standard]). See
Instructions to Authors for a complete description of levels of evidence.

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