Provocative Testing of Segmental Artery Feed to the Anterior Spinal Cord Prior To Ligation With Transcranial Electric Motor Evoked Potentials**

Purpose: There is ongoing controversy as to the risk of paraplegia from segmental artery ligation during anterior spinal fusion. While somatosensory evoked potentials have been used to test indirectly for spinal cord ischemia following temporary segmental artery occlusion, the potential for a false-negative finding is high because the SSEP is dorsal column mediated. The purpose of this study was to determine if transcranial electrical motor evoked potentials (TceMEPs) could provide a more sensitive, direct test for identifying nutrient feeding segmental arteries that are critical to anterior spinal motor tract function prior to vessel ligation.

Methods: TceMEPs were recorded from bilateral quadriceps, tibialis anterior and/or abductor hallucis muscles as well as from an upper extremity control muscle group, both prior to and 2-3 minutes following test occlusion of each candidate segmental artery. If post-occlusion tceMEP amplitudes did not change, the vessel was permanently ligated. If, however response amplitude over one or more lower extremity muscles was diminished by >50%, the clamp was released until complete amplitude recovery. If on subsequent reclamping, tceMEP amplitudes again diminished (>50%), no permanent ligation was performed.

Results: Significant tceMEP changes following temporary vessel occlusion were noted in eight (6.0%) of 150 pediatric patients in this series. In two patients, the tceMEP changes were correlated with hypotension (MAP< 55 mm Hg), which resolved upon elevating the MAP to 90 mm Hg, thereby allowing for permanent vessel ligation. For the remaining six patients (4.0%), however, tceMEPs could be restored only by removal of the test clamp. Consequently, no permanent ligation was performed to avoid post-operative motor deficit. No patient emerged with new motor deficit following surgery, as predicted by unchanged tceMEPs at closing.

Conclusion: TceMEPs provide a rapid, valid and reliably sensitive technique for identifying segmental arteries that may be nutrient feeders to the anterior spinal cord. If ligated, such segmental vessels may predispose the patient to neurologic deficit particularly during the application of strong corrective forces applied to spinal instrumentation.

** The FDA has not cleared a drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed in an “off-label” use).