Abstract
Background:
Spinal deformity surgery carries the risk of loss of neurological function which may be permanent. Although the overall the incidence is low it is much higher in complex congenital deformities or those with pre-existing myelopathy. Intra-operative spinal cord monitoring allows this risk to be reduced by providing feedback to the surgeon while the corrective manoeuvres are performed.
Although ideally a trained technician with multimodal monitoring is recommended, it is often not an option in a resource limited environment and surgeon operated technology is used.
Aim:
to evaluate the use of surgeon operated trans-cranial motor evoked potentials (tcMEP) in spinal deformity surgery
Methods:
A retrospective review was conducted on a single surgeon series of 108 consecutive cases utilising the NIM system (Medtronic). Percutaneous needles were employed in the scalp, both hands and feet to allow the upper limbs to act as controls.
Forty-nine patients were 13 years old or less, 47 were 14–18, and 12 adults. The cohort consisted of 54 AIS, 27 neuromuscular scoliosis, 14 congenital, 2 old TB and 11 miscellaneous. The vast majority were posterior based procedures.
Results:
In 4 cases initial traces could not be obtained. One was a severe myelopathy and further efforts to monitor were abandoned. In one case the anaesthetist had broken protocol and once converted to TIVA the traces improved. Two others were poor initially but improved as the case progressed. In 8 cases intra-operative traces were lost. One was thought to be due to hypothermia and the patient woke intact. Two were unrelated to surgical intervention and recovered spontaneously with patients waking intact. Four cases deteriorated during the corrective manoeuvre (one delayed) and recovered with reduction of correction. One case required removal of instrumentation after repeated loss each time rods were inserted and awoke with a weak leg but recovered and was re-operated two weeks later.
Conclusion:
Surgeon operated tcMEP's allows feedback in terms of safety of deformity correction with a 100% negative predictive value and an 8% incidence of signal loss during correction allowing immediate remedial action.
