The clinical situation describes a patient who has neuromonitoring abnormalities following placement of an interbody cage. Loss of sensory and motor signals have been shown to be predictive of an injury to the spinal cord. As there was a direct temporal correlation with the placement of the cage, it should be immediately removed and followed by repeated neuromonitoring signal testing.
In a retrospective, single-surgeon study, Bose et. al reviewed SSEP and tceMEP readings during anterior cervical spine surgery. They concluded that SSEPs and tceMEPs can be used simultaneously to indirectly and directly monitor spinal cord motor function, respectively.
In a prospective cohort study, Hillibrand et al compared SSEPs to tceMEPs during anterior cervical spine surgery and found that tceMEPs are more sensitive and specific than SSEPs in monitoring motor tract injury. In addition, they showed decreases in motor signals by tceMEP were identified earlier than decreases in sensory signals by SSEPs.
A recent review article by Devlin discusses neuromonitoring in detail and includes relevant spinal cord anatomy and neuromonitoring modalities. tceMEPs provide direct monitoring of the corticospinal tracts. SSEPs allow for direct monitoring of the dorsal sensory columns and allow for indirect assessment of the ventral motor tracts, see Illustration A.
Bose B, Sestokas AK, Schwartz DM. Neurophysiological monitoring of spinal cord function during instrumented anterior cervical fusion. Spine J. 2004 Mar-Apr;4(2):202-7.
PMID:15016399 (Link to Abstract)
Hilibrand AS, Schwartz DM, Sethuraman V, Vaccaro AR, Albert TJ. Comparison of transcranial electric motor and somatosensory evoked potential monitoring during cervical spine surgery. J Bone Joint Surg Am. 2004 Jun;86-A(6):1248-53.
PMID:15173299 (Link to Abstract)
Devlin VJ, Schwartz DM. Intraoperative neurophysiologic monitoring during spinal surgery. J Am Acad Orthop Surg. 2007 Sep;15(9):549-60.
PMID:17761611 (Link to Abstract)