Ultrasonographic versus EMG Properties of the Lumbar Plexus via a Lateral Retroperitoneal Surgical Approach: A Live Human Validation Study

Presented at SMISS Annual Forum 2016
By Jim Youssef MD
With Kern Singh MD, Douglas Orndorff MD, Trong Nguyen MS, Sue Myhre PhD,

Disclosures: Jim Youssef MD A; Spinal Research Foundation, NuVasive, BioSurface Engineering Technologies, Globus Medical, ARTM, Axial Biotech, Vertiflex, Integra. B; NuVasive, Integra, Amedica. D; Amedica, Pioneer, Vertiflex, Be Kern Singh MD A; CSRS Resident Grant. B; DePuy, Zimmer, Stryker, CSRS, ISASS, AAOS, SRS, Vertebral Column - ISASS. D; Avaz Surgical, LLC, Vital 5, LLC. F; Zimmer, Stryker, Pioneer, Lippincott Williams & Wilkins, Th, Douglas Orndorff MD A; Globus Medical, SeaSpine, Vertiflex, Nuvasive. B; Nuvasive, SeaSpine, Stryker. F; SeaSpine., Trong Nguyen MS None, Sue Myhre PhD None,


Electromyography (EMG) neuromonitoring is currently used to navigate the psoas muscle during a lateral lumbar interbody fusion (LLIF). Although the current neural guidance systems are valuable and have decreased the incidence of neuropraxia, these systems do not allow a direct identification of the lumbar plexus. Additionally, EMG neuromonitoring can be impacted by patient co-morbidities and anesthetic agents. Quantitative ultrasound (QUS) imaging may be a possible alternative and/or compliment to currently used EMG neuromonitoring. QUS can provide both real-time, user-friendly images of the lumbar plexus and proximal auditory responses with the added ability to concurrently detect vascular structures and sensory nerves.


To assess and compare a QUS’s discerning and visual capabilities of the lumbar plexus, peripheral nerves and surrounding tissues during a live human lateral retroperitoneal surgery to a standard EMG system.


Four patients (2 = 1 level; 2 = 2 level) underwent an LLIF (L3-4 and L4-5) with the standard of care neuromonitoring (NVM5®, NuVasive, Inc., San Diego, CA). The orientation and thresholds were recorded after the lateral fusion procedure was completed. The surgeon post-procedure acquired QUS (Aurotech, Tydal, Norway and Avaz Surgical, Chicago, IL) images of the lumbar plexus, peripheral nerves and surrounding vasculature. Descriptive characteristics of the nerves and vascular structures were collected via video and images obtained by the ultrasound transducer. 


The EMG thresholds recorded during the dilation of the psoas muscle, anteriorly, posteriorly, superiorly and inferiorly, respectively were: Patient 1 = 11, 7, >20, >20 and >20, 4, 15, >20; Patient 2 = >20 in all directions; Patient 3 = >20, >20, >20, 19 and >20 in all directions; and Patient 4 = 13, 6, 9, 10. The presence or absence of nerves via ultrasound was deemed present in all four patients in all four directions. The genitofemoral nerve (sensory) was identified by the QUS in all four patients; however, the nerve was not detected by the EMG neuromonitoring system. 


Our pilot data demonstrated that the sensitivity and specificity of the QUS were accurate in identifying both motor and sensory nerves. QUS appears to be an efficacious and advantageous tool for surgeons employing a lateral retroperitoneal procedure. With the ability to designate a safe route by identifying and thus avoiding neural and vasculature structures, surgeons will be able to optimize the intraoperative safety and reduce post-operative complications of their patients. More data is needed to improve the QUS algorithm.