Saphenous Nerve Somatosensory Evoked Potentials Monitoring during Lateral Interbody Fusion

Abstract

Introduction Lateral transpsoas interbody fusion (LIF) is a novel minimally invasive technique reducing risks related to traditional anterior approaches. Despite advantages, transpsoas exposure carries up to 30% risk of lumbar plexus injury. Intraoperative neuromonitoring is utilized to prevent postoperative deficits, but to date there is no reliable technique to detect upper lumbar plexus injury. Materials and Methods Saphenous nerve somatosensory-evoked potentials (SSEPs) were obtained by stimulation of inferior medial thigh with needle electrodes and recording from scalp. Primary outcome was measured by testing reproducibility of SSEPs at baseline, changes during procedure, and relevance to standard modalities. Intraoperative changes were identified and correlated to primary outcome. Results A total of 38 patients were included in the study (average age 63.5 years, 25 females, 13 males) and underwent surgery on 88 total levels. Reliable saphenous SSEPs were recorded bilaterally in 34 of 38 patients. Reduction of amplitude > 50% in two cases was observed during expansion of the tubular retractor. The posterior tibial SSEP remained unchanged. The saphenous returned to baseline after collapsing the retractor and no clinical deficits were observed. Conclusion Saphenous SSEPs can be used to detect electrophysiological changes to prevent femoral nerve injury during LIF. A larger sampling size is underway as to validate whether this technique offers increased sensitivity/specificity, and correlates with the postoperative outcomes.