Multimodality Monitoring During Transpsoas Lateral Access To the Spine – A Multicenter Study Justin Silverstein, DHSc, CNIM Neuro Protective Solutions, LLC Spine Medical Services, PLLC Long Island NY Jon Block DC,CNIM ION Intraoperative Neurophysiology, LLC Walnut Creek, CA NEUROMONITORING Goal: To protect the main motor branches of the lumbar plexus with an intraoperative functional assessment. • Motor branches to protect: 1. Abdominal Innervation: Subcostal (T12,last thoracic intercostal), Illioinguinial & Illiohypogastric) 2. Obturator Nerve 3. Femoral Nerve Most feared neurological complication is damaging the femoral nerve. • There is risk of FEMORAL NERVE injury during these procedures • This injury is NOT RADICULAR in nature but is a LUMBAR PLEXOPATHY or FEMORAL NEUROPATHY • Use of Triggered EMG can only give proximity to the nerve but CANNOT assess the function of the nerve AHMADIAN, et al. (2012). Spine 12: 755. Femoral Nerve Anatomy • Left lateral view of a left sided specimen, made after dissection of the psoas muscle (PS). The spinous processes would be at the right side of the image (not visible). Outlines show the approximate locations of the vertebral bodies, disc spaces and pedicles. Transverse processes (TP) are also outlined. L3 TP PS Note the close proximity of the L4-5 needle (at a mid-disc location in green) and the fully formed trunk of the femoral nerve. Source: Lumbar Plexus Anatomy within the Psoas Muscle: Implications for the Transpsoas Lateral Approach to the L4-L5 Disc Timothy T. Davis, MD, Hyun W. Bae, MD, MAJ James M. Mok, MD, MC, USA, Alexandre Rasouli, MD, and Rick B. Delamarter, MD L4 TP Neuromonitoring Goals: • To provide a functional assessment of function throughout the procedure. • Detecting a reduction in neural function can provide an early alert to surgeons of impending neurological damage so that immediate action can be taken to avoid permanent damage. • The presence of evoked responses can provide the surgeon with the confidence to continue the discectomy and arthrodesis placement, therefore reducing constraints on retraction time. “Multi-modal neuromonitoring” consists of 2 Types of Evoked Potentials Saphenous Somato-Sensory Evoked Potentials (SSEPs) Motor Evoked Potentials (MEPs) Neurodiagn J. 55:1–10, 2015 © ASET, Missouri Motor Evoked Potentials for Femoral Nerve Protection in Transpsoas Lateral Access Surgery to the Spine Jon Block, D.C., CNIM1; Justin W. Silverstein, DHSc, CNIM, R. EP T. R.NCS.T., CNCT, Hieu T. Ball, M.D.4; Laurence E. Mermelstein, M.D.5; Hargovind S. DeWal, M.D.5;Rick Madhok, M.D.6; Sushil K. Basra, M.D.5; Matthew J. Goldstein, M.D.7 1ION Intraoperative Neurophysiology, LLC Walnut Creek, California 2Neuro Protective Solutions, LLC Commack, New York 3Spine Medical Services, PLLC Walnut Creek, California 4California Comprehensive Spine Institute, Inc. San Ramon, California 5Long Island Spine Specialists, PC Commack, New York 6Neuroaxis Neurosurgical Associates, PC Kew Gardens, New York 7Orthopedic Associates of Manhasset, PC Great Neck, New York ABSTRACT. Detecting potential intraoperative injuries to the femoral nerve should be the main goal of neuromonitoring of lateral lumber interbody fusion (LLIF) procedures. We propose a theory and technique to utilize motorevoked potentials (MEPs) to protect the femoral nerve (a peripheral nerve), which is at risk in LLIF procedures. MEPs have been advocated and widely used for monitoring spinal cord function during surgical correction of spinal deformity and surgery of the cervical spine, but have had limited acceptance for use in lumbar procedures. This is due to the theoretical possibility that MEP recordings may not be sensitive in detecting an injury to a single nerve root secondary to overlapping muscle innervation of adjacent root levels. However, in LLIF procedures, the surgeon is more likely to encounter lumbar plexus elements, including peripheral nerves, than nerve roots. Within the substance of the psoas muscle, the L2, L3, and L4 nerve roots combine to form the trunk of the femoral nerve. At the point where the nerve roots become the trunk of the femoral nerve, there is no longer any alternative overlapping innervation to the quadriceps muscles. Insult to the fully formed femoral nerve, which completely blocks conduction in motor axons, should theoretically abolish all MEP responses to the quadriceps muscles. On multiple occasions over the past year, our neuromonitoring groups have observed unilateral (surgical-side-only) femoral motor and/or sensory evoked potential intraoperative changes, many of which resolved with a surgical intervention (i.e., prompt removal of surgical retraction). Corresponding Author’s Email: [email protected] Received: September 16, 2014. Accepted for publication: November 21, 2014. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/utnj. 1 Preserving femoral nerve function: A review of multimodality neuromonitoring in 97 transpsoas J Silverstein, DHSc, CNIM, J Block, DC, CNIM, M Goldstein, MD, R Madhok, MD, S Basra, MD, L Mermelstein, MD, H DeWal, MD, H Ball, MD & J Dowling. Being Presented at ISASS 2015 – San Diego • A multi-center group of board certified neurophysiologists, fellowship trained orthopedic spine and neurological surgeons performed and monitored 97 lateral transpsoas procedures over the course of one year. • Saphenous SSEPs and Motor evoked potentials from the approach side quadriceps was performed • 2 patients exhibited a loss of the approach side sSSEP concurrently with a loss of the quadriceps MEP responses while the retractors were in place. • With removal of the retractors, the responses from both modalities returned to baseline values and no new neurological deficits were observed • 1 patient exhibited a loss in the sSSEP with return to baseline after intervention (MEPs were not obtained at baseline in this case). • In 6 procedures, quadriceps MEPs were recorded at baseline and were lost following placement of the retractors (with sSSEPs unobtainable at baseline in these cases) • Removal of retractors showed a full return of MEPs to baseline in 5 patients with no new post-op neurological deficits noted. • Patient 6 exhibited postoperative ipsilateral quadriceps palsy; however, this case was early on in our adoption of the MEP technique and proper technique and interventional protocols were not yet in place. • We also had one patient exhibit transient thigh paresthesia without intraoperative SSEP or MEP detection • We report a sensitivity of 92% and a specificity of 100%, with a PPV of 100% and a NPV of 99%. Case Study: • Lateral L4-5 procedure with a concurrent loss of the surgical side Sapehnous SSEPs and a loss of only the surgical side quadriceps MEPs. • All other Posterior Tibial and the contralateral Saphenous SSEPs and all other MEP responses were unchanged. • Informed surgeon of loss of sensory and motor evoked potentials at the time when the discectomy was complete, trial size was established and he was preparing for the final implant. • Surgeon hastened the insertion of the implant and removed the retraction as soon as was possible. • The lost Saphenous SSEP and MEPs quickly returned to baseline values. L Quadriceps R Quadriceps MEPs March 2015 Case Study: Loss of Quadriceps MEPs & Saphenous SSEPs during the discectomy in an L4-5 Trans-psoas Discectomy & Fusion Post operative exam: Knee extension reported as 3/5 strength down from 5/5 pre-operatively Saphenous SSEPS PTN SSEPS Ipsilateral Saphenous SSEPS Ipsilateral Waterfall Contralateral Waterfall Motor Evoked Potentials: Ipsilateral Muscle Recordings Vastus Medialis Tibialis Anterior Gastrocnemius Adductor Hallucis Motor Evoked Potentials: Ipsilateral Muscle Recordings Vastus Medialis Tibialis Anterior Gastrocnemius Adductor Hallucis Jon Block, DC, CNIM & Justin Silverstein, MS, CNIM Neurodiagnostic J. 54 (4) Dec 2014. Motor Evoked Potentials for Femoral Nerve Protection in Transpsoas Lateral Access Surgery to the Spine J Block, DC, CNIM, J Silverstein, DHSc, CNIM, H Ball, MD, L Mermelstein, MD, R Madhok, MD, M Goldstein, MD, S Basra, MD, & H DeWal, MD Neurodiagnostic J. 55(1): In press Mar 2015 3/19/2015 The Monitor- ASNM’s Monthly Newsletter November 2014 Variable Results in Motor Mapping of the Lumbar Plexus: A Comparison of 3 Different L2-L3 Far Lateral Lumbar Discectomy & Fusion Procedures Justin Silverstein, MS, CNIM, Jon Block, DC, CNIM, Sushil Basra, MD Spine Medical Services, PLLC, ION Intraoperative Neurophysiology, LLC, Long Island Spine Specialists, PC There has been a major trend in surgery towards less invasive procedures performed through smaller surgical apertures. Smaller surgical openings are associated with decreased visualization, and surgeons must rely more on intraoperative tools including fluoroscopic imaging and motor nerve mapping techniques to assess their relative anatomical position and proximity to neural structures respectively. In retroperitoneal lateral lumbar interbody fusion (LLIF) procedures, the surgeon must establish a safe surgical corridor to access the disc space by traversing through the substance of the psoas muscle while avoiding damage to the lumbar plexus. Surgeons utilize Triggered EMG (T-EMG) using a monopolar electrical probe to detect the presence and proximity of lumbar plexus elements in the surgical field. A detailed understanding of the functional anatomy of the lumbar plexus and an appreciation of anatomical variants is essential to understanding how to effectively map the lumbar plexus. Anloague and Huijbregts (2009) describe a prevalence of anatomical variation ranging between 8.8-47.1% in the individual nerves of the lumbar plexus with a mean prevalence of 20.1%. No clear guidelines for muscle selection in LLIF procedures have been established. In this article, the authors describe their personal experience and rationale for selection of essential muscle recordings for LLIF procedures at the L2-3 level. We present 3 separate L2-3 LLIF procedures that illustrate the variability of lumbar plexus elements that may be encountered at the same surgical level in different patients. At the L2-L3 Level, we recommend the following essential T-EMG muscle recordings to assist in the navigation of the lumbar plexus: Abdominal Muscles: The major elements of the upper lumbar plexus include multiple nerves that innervate the abdominal muscles including the Subcostal (T12), Illiohypogastric (T12, L1) and Illioinguinial (L1) nerves. Gaining access to the retroperitoneal space and traversing the abdominal wall poses a risk of injury to these major nervous structures and abdominal wall paresis is an associated complication of the LLIF procedure. (Ahmadian, Deukmedjian, Abel, Dakwar, & Uribe, 2013; Dakwar et al, 2011). The authors have often observed T-EMG responses from abdominal muscle recordings that have been useful in alerting the surgeon of the presence of neural elements in the surgical field. (Figure 1). Adductors:The Obturator nerve is formed by the L2, L3, & L4 roots and descends through the Psoas muscle to innervate the major muscle group for leg adduction. Figure 2 illustrates an example where motor mapping at the L2-3 level resulted in T-EMG responses limited to the adductor muscle recording channel suggesting proximity to the Obturator nerve. Quadriceps:The femoral nerve (L2, L3, & L4) innervates the quadriceps muscles. Anterior thigh pain, paresthesia and diminished knee extension are complications associated with a femoral nerve injury in LLIFs. (Ahmadian, Deukmedjian, Abel, Dakwar, & Uribe, 2013). We recommend using multiple quadriceps muscle recordings (i.e. rectus femoris & vastus medialis). Figure 3 illustrates an example where motor mapping at the L2-3 level resulted in TEMG responses from multiple quadriceps muscles in addition to adductor muscle responses suggesting proximity to both the Femoral and Obturator nerves. Although more study is needed, the authors recommend the utilization of abdominal, adductor and quadriceps muscle recordings when mapping the lumbar plexus in L2-3 LLIF procedures. Conclusions: • • Saphenous SSEPs can be recorded to detect electrophysiological changes and prevent femoral nerve injury during lumbar trans-psoas interbody fusion. Larger sampling size is underway to validate whether addition of this technique offers increased sensitivity and/or specificity, and helps to reduce the risk of postoperative neurological deficits. Limitations • These techniques requires the presence of a QUALIFIED NEUROPHYSIOLOGY PROFESSIONAL for the establishment of baseline potentials and to monitor the potentials in a continuous fashion. • The saphenous nerve SSEP was not able to be established at baseline in 10% of the patients during our pilot study. • In our Second Study: Saphenous SSEP were not obtained in 6% (6/97) of the patients and MEPs to the Quadriceps were not obtained in 6% (6/97) of the patients Closing Thoughts Monitoring: • SSEP • Saphenous nerve SSEP - Monitors Femoral nerve function • Continuous recordings provide valuable information about the functional integrity of the femoral while the retractors are in place. • This is especially important at the L3-4 and L4-5 Levels. • Upper Extremity SSEPs should be monitored for potential positional injuries and to assess the effects of anesthetics on evoked potentials • Other SSEPs can be used as controls, to assess global quada equina function, to assess positional leg issues and nerve root stretching caused by arthrodesis placement (Duncan et al, 2012) • Posterior TIbial Nerve SSEP • Deep Peroneal SSEP Closing Thoughts Monitoring: • MEP • MEPs SHOULD be used as complimentary information to assess peripheral nerve function (i.e. femoral nerve and obturator nerve). • The utility of MEPs in detecting alterations in nerve root function is unclear • MEP responses are recorded from the same muscles used for EMG • Combined with Saphenous SSEPs, MEPs may provide redundant information regarding femoral nerve function. • MEPs are only beneficial if quad muscles are obtained. • AHL muscle used as control to ensure MEPS are present. • MEPs should be assessed periodically following final retractor placement, discectomy and arthrodesis placement. Thank you! Intraoperative Neurophysiology Jon Block DC,CNIM www.smsneuro.com ION Intraoperative Neurophysiology 951 Country Lane Walnut Creek, CA 94596 [email protected] (678) 977-6666 www.npsneuro.com Contact: [email protected] Manual T-EMG Threshold Technique Manually determining motor threshold level Stimulation intensity manually controlled Key Concept: Motor Mapping must be differentiated from Monitoring Nerve Function • The presence of a Triggered EMG response does not provide the surgeon with evidence of functional continuity of plexus elements Rationale: Even if a nerve is surgically transected, the distal segment of the nerve will remain electrically excitable for approximately 24-48 hours until degeneration of the distal segment takes effect. Monitoring the function of the nerves of the lumbar plexus throughout the procedure requires the utilization sensory and motor evoked potentials. 48 hours later
© Copyright 2024