Evaluation of intraoperative nerve-monitoring during insertion of an iliosacral implant in an animal model.
BACKGROUND
The use of continuous electromyographic and somatosensory-evoked-potential monitoring systems has been advocated to assist in avoiding nerve-root injury during operations on the pelvic ring. More recently, it was suggested that stimulus-evoked electromyographic monitoring may further decrease the risk of iatrogenic nerve-root injury during posterior pelvic fixation by enabling the surgeon to determine the actual distance of an implant from a nerve root. The purpose of the current study was to evaluate the relative efficacy of these three methods of monitoring for minimizing the risk of neural injury during the placement of iliosacral implants.


METHODS
While the function of the first sacral nerve root was monitored with the use of stimulus-evoked electromyographic, continuous electromyographic, and somatosensory-evoked-potential monitoring techniques, a 2.0-millimeter stainless-steel Kirschner wire was progressively inserted, guided by a high-speed computerized tomographic scanner, into the first sacral body of seventeen hemipelves in nine dogs. The end point was contact with the nerve as demonstrated by the computerized tomographic images. It was expected that this end point would be heralded by a burst of spontaneous electromyographic activity and an abnormal somatosensory-evoked-potential signal. Anatomical dissection at the completion of the study documented the final position of the Kirschner wire.


RESULTS
Anatomical dissection demonstrated compression or penetration of the nerve root in sixteen of the seventeen specimens. A spontaneous burst of electromyographic activity was not recorded for any specimen on continuous electromyographic monitoring; this finding was significantly different from what had been expected (p<0.001). Because of technical problems, somatosensory evoked potentials could be recorded for only twelve hemipelves that had nerve-root compression or penetration, and abnormal somatosensory evoked potentials were recorded for only one of the twelve; this finding was significantly different from what had been expected (p<0.001). A total of 113 stimulus-evoked electromyographic data points were obtained. The correlation coefficient for the relationship between the current threshold recorded with stimulus-evoked electromyographic monitoring and the distance of the wire from the nerve was 0.801 (p<0.001). The actual measured current thresholds were of an observed proportion not different from what had been expected (p = 0.48).


CONCLUSIONS
Continuous electromyographic and somatosensory-evoked-potential monitoring techniques failed to indicate contact with the nerve root reliably in this animal model. However, stimulus-evoked electromyographic monitoring consistently provided reliable information indicating the proximity of the implant to the nerve root.
Moed
B R
BR
Henry Ford Hospital, Detroit, Michigan 48202, USA.
Hartman
M J
MJ
Ahmad
B K
BK
Cody
D D
DD
Craig
J G
JG
D000818:Animals; D001864:Bone Wires / Q000009:adverse effects; D004056:Differential Threshold; D004195:Disease Models, Animal; D004210:Dissection; D004285:Dogs; D004558:Electric Stimulation; D004576:Electromyography; D005069:Evaluation Studies as Topic; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D007049:Iatrogenic Disease; D007085:Ilium / Q000601:surgery*; D007430:Intraoperative Care; D007431:Intraoperative Complications / Q000517:prevention & control*; D009408:Nerve Compression Syndromes / Q000209:etiology; D015203:Reproducibility of Results; D012307:Risk Factors; D012447:Sacrum / Q000601:surgery*; D012684:Sensory Thresholds; D013126:Spinal Nerve Roots / Q000293:injuries / Q000502:physiology*; D013193:Stainless Steel; D015898:Tomography Scanners, X-Ray Computed
D013193:Stainless Steel