Triggered EMG Potentials in Determining Neuroanatomical Safe Zone for Transpsoas Lumbar Approach: Are They Reliable?. Issue 11 (June 2016)

• Record Type: Journal Article
• Authors: Sarwahi, Vishal; Pawar, Abhijit; Sugarman, Etan; Legatt, Alan D.; Dworkin, Aviva; Thornhill, Beverly; Lo, Yungtai; Wendolowski, Stephen F.; Gecelter, Rachel C.; Moguilevitch, Marina
• Is Part Of: Spine. Volume 41:Issue 11(2016)
• Page Start: E647
• Page End: E653
• Publication Date: 2016-06
• Subjects: large animal study -- LLIF -- neuromapping -- psoas hematoma -- safe zone -- threshold EMGs -- triggered EMGs; Spine -- Abnormalities -- Periodicals; Spine -- Diseases -- Periodicals; Spine -- Surgery -- Periodicals; 616.73005
• DOI: 10.1097/BRS.0000000000001381
• Languages: English
• ISSNs: 0362-2436

Abstract

Abstract : Study Design: In vivo analysis in swine model. Objective: The purpose of this study was to determine the accuracy of triggered EMG (t-EMG) and its reliability in lateral lumbar interbody fusions surgery. We also aim to document changes in psoas muscle produced during the approach. Summary of Background Data: Lateral lumbar interbody fusions is preferred over direct anterior approach because of lower complications, blood loss, and shorter recovery time. Threshold-EMGs are utilized for real-time feedback about nerve location; however, neurological deficits are widely reported, and are unique to this approach. Multiple factors have been hypothesized including neuropraxia from retractors and compression from psoas hematoma/edema. The variable reports of neurological complication even with t-EMGs indicate the need to study them further. Methods: Eight swines underwent left-sided retroperitoneal approach. The nerve on the surface of the psoas was identified and threshold-EMGs were obtained utilizing a ball-tip, and needle probe. First EMG and threshold responses required to elicit 20-μV responses were recorded for 2 mm incremental distances up to 10 mm. In the second part, a K-wire was inserted into the mid-lumbar disc space, and a tubular retractor docked and dilated adequately. Postmortem CT scans were carried out to evaluate changes in psoas muscle. Results: A t-EMG stimulus threshold of <5 mA indicates a higher probability that the probe is close to or on the nerve, but this was not proportional to the distance suggesting limitations for nerve mapping. Negative predictive value of t-EMGs is 76.5% with the ball-tipped probe and 80% with the needle probe for t-EMG ≥10 mA and indicates that even with higher thresholds, the nerve may be much closer than anticipated. Postoperative hematoma was not seen on CT scans. Conclusion: Threshold measurements are unreliable in estimating distance from the nerve in an individual subject and higher values do not always correspond to a 'safe zone." Level of Evidence: 5