Introduction Spinal cord monitoring in posterior scoliosis surgery has become a standard of care. It has been our practice since 1999, to monitor the somato-sensory potential (SEP) and motor evoked potential (MEP) in all posterior cases. We report on and discuss the meaning of alteration in the spinal cord monitor signal that occurred in 15 cases from a total of 165 procedures.

Methods This is a retrospective review of patients from a hospital database. Over a six year period, 167 posterior scoliosis instrumented fusion procedures were performed by paired combinations of the four authors. In 13 cases we have been alerted to a change in one or both signals during the procedure. Associated with these, were two cases of intra-operative cardiac arrest, and six cases of post-operative neurological deficit. All patients remain under continued regular review.

Results In the two cases of intra-operative cardiac arrest, the SEP and MEP signals were lost approximately three minutes prior to the arrest. Both patients had neurological deficits post-operatively, one has totally recovered, and one has a residual complex regional pain syndrome of the right leg. This last patient is the only one of six who has not had complete resolution of the post-operative neurological deficit. In five of the six cases who sustained post-operative neurological deficits, the SEP and usually the MEP was lost and did not return. In the sixth case, the SEP did return. In the remaining seven cases, there were changes of decreased amplitude or increased latency in the SEP or MEP that did not appear to result in a postoperative clinical consequence, however; in two patients, signal changes were directly related to changes in blood pressure, and in two other patients, signal changes were directly related to concave hook placement.

Discussion On review of the management and outcome of these cases, we conclude that profound hypotension will alter the SEP and may herald a catastrophic cardiovascular or neurological event. Furthermore, the modality of continuous spinal cord monitoring can provide specificity in the diagnosis of an actual or impending neurological insult and allow for appropriate and timely intervention. We believe spinal cord monitoring in the posterior approach for spinal deformity is an invaluable tool, and is in fact, mandatory for all idiopathic and ambulant non-idiopathic spinal deformities.