9. Multimodal intraoperative evoked potential monitoring (IOM) for hip surgery

Introduction The incidence of sciatic nerve palsy after hip surgery ranges from 2.7% in primary total hip arthroplasty up to 7.6% in developmental dysplasia surgery. So far, intraoperative monitoring using multimodal evoked potential for hip surgeries to assess sciatic and femoral nerves functional integrity has not been described. Material and methods Thirty patients who underwent hip surgery using IOM of sciatic and femoral nerves have been evaluated. All the patients received total intravenous anaesthesia. Multimodal IOM includes: (a) somatosensory evoked potentials (SEP) and (b) motor evoked potentials (MEP) recorded bilaterally in lower extremities limb muscles from quadriceps, tibialis anterior, gastrocnemius, peroneal and abductor hallucis bilaterally. In addition, we also have developed a new IOM technique: (c) posterior root muscle reflex (PRMR) and (d) anterior root muscle response (ARMR). To elicit PRMR and ARMR, percutaneous stimulation of cauda equine was performed by self-adhesive electrodes placed over the skin of the projection of the first and third lumbar interspinous space (anode) and over the abdomen skin of the umbilicus (cathode). A paired stimuli of identical parameters are used with an interstimulus interval of 50 ms and duration of 0.5–1 ms. The recording electrodes for PRMR and ARMR were identical as the electrodes used for recording MEPs. Results Baselines were successful in all patients. Detection of significant changes occured in eight patients (8/30, 26,6%). In six patients (6/30, 20%) changes were reversible and in two patients (2/30, 6,7%) changes were irreversible and correlated with the postoperative neurological deficit. Conclusion Multimodal IOM techniques applied to hip surgery allow identification of the momentthat may damage peripheral nerves of roots before an irreversible injury occurred and/or avoid permanent postoperative neurological deficits. PRMR and ARMR could emerge as a new intraoperative monitoring techniques to assess the functional integrity of lumbosacral plexus and nerves. These new techniques have potential to give more specific information than MEPs and SEPs.