Four-limb muscle motor evoked potential and optimized somatosensory evoked potential monitoring with decussation assessment: results in 206 thoracolumbar spine surgeries

The objective of this study was to improve upon leg somatosensory-evoked potential (SEP) monitoring that halves paraplegia risk but can be slow, miss or falsely imply motor injury and omits arm and decussation assessment. We applied four-limb transcranial muscle motor-evoked potential (MEP) and optimized peripheral/ cortical SEP monitoring with decussation assessment in 206 thoracolumbar spine surgeries under propofol/opioid anesthesia. SEPs were optimized to minimal averaging time that determined feedback intervals between MEP/SEP sets. Generalized changes defined systemic alterations. Focal decrements (MEP disappearance and/or clear SEP reduction) defined neural compromise and prompted intervention. They were transient (quickly resolved) or protracted (> 40 min). Arm and leg MEP/SEP monitor-ability was 100% and 98/97% (due to neurological pathology). Decussation assessment disclosed sensorimotor non-decussation requiring ipsilateral monitoring in six scoliosis surgeries (2.9%). Feedback intervals were 1-3 min. Systemic changes never produced injury regardless of degree. They were gradual, commonly included MEP/SEP fade and sometimes required large stimulus increments to maintain MEPs or produced > 50% SEP reductions. Focal decrements were abrupt; their positive predictive value for injury was 100% when protracted and 13% when transient. Six transient arm decrements predicted one temporary radial nerve injury; five suggested arm neural injury prevention (2.4%). There were 15 leg decrements: six MEP-only, four MEP before SEP, three simultaneous and two SEP-only. Five were protracted, predicting four temporary cord injuries (three motor, one Brown-Sequard) and one temporary radiculopathy. Ten were transient, predicting one temporary sensory cord injury; nine suggested cord injury prevention (4.4%). Two radiculopathies and one temporary delayed paraparesis were unpredicted. The methods are reliable, provide technical/systemic control, adapt to non-decussation and improve spinal cord and arm neural protection. SEP optimization speeds feedback and MEPs should further reduce paraplegia risk. Radiculopathy and delayed paraparesis can evade prediction.