Low Posterior Electromyographic Threshold and Functional Outcomes After L4-5 Lateral Lumbar Interbody Fusion

Abstract

BACKGROUND AND OBJECTIVES: – The transpsoas approach for lateral lumbar interbody fusion (LLIF) places the surgical retractor near the lumbar plexus, particularly at the L4-5 level. To mitigate risk to these nerves, surgeons rely on intraoperative neuromonitoring using stimulation to approximate the distance between the plexus and retractor. The aim of this study was to review a single-institution series of lateral-position LLIF procedures to determine whether the stimulation threshold was associated with plexus injury.METHODS: – Single-level LLIF procedures performed in the lateral decubitus position at L4-5 from January 2019 to May 2022 with neuromonitoring data and retractor time available were included. Patients without available neuromonitoring data and whose treatment included additional levels were excluded. Basic demographic and case-specific data were extracted. Outcome measures included postoperative lower extremity paresthesia and motor deficits. Descriptive statistics were performed to characterize the data set. Spearman correlation was performed to evaluate associations between variables.RESULTS: – Forty-two patients with a mean (SD) age of 66 (9.8) years who underwent single-level L4-5 LLIF in the lateral position with intraoperative neuromonitoring data were included. The mean retractor time was 12.4 (5.0) minutes. The mean posterior electromyography (EMG) threshold was 10.4 (10.1) mA. One patient (2%) experienced femoral nerve motor neurapraxia; 16 (38%) reported sensory neurapraxia (anterior thigh numbness) at 6 weeks postoperatively, which decreased to 0% at 6 months postoperatively. A posterior EMG threshold was not associated with femoral nerve motor neurapraxia or sensory neurapraxia 6 weeks postoperatively on one-way analysis of variance and univariate logistic regression, respectively.CONCLUSION: – No significant association was found between posterior EMG threshold and femoral nerve motor neurapraxia or sensory neurapraxia after single-level L4-5 lateral position LLIF.