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Saphenous somatosensory-evoked potentials monitoring of femoral nerve health during prone transpsoas lateral lumbar interbody fusion



To assess whether saphenous somatosensory-evoked potentials (saphSSEP) monitoring may provide predictive information of femoral nerve health during prone lateral interbody fusion (LIF) procedures.


Intraoperative details were captured prospectively in consecutive prone LIF surgeries at a single institution. Triggered electromyography was used during the approach; saphSSEP was monitored throughout using a novel system that enables acquisition of difficult signals and real-time actionable feedback facilitating intraoperative intervention. Postoperative neural function was correlated with intraoperative findings.


Fifty-nine patients (58% female, mean age 64, mean BMI 32) underwent LIF at 95 total levels, inclusive of L4-5 in 76%, fixated via percutaneous pedicle screws (81%) or lateral plate, with direct decompression in 39%. Total operative time averaged 149 min. Psoas retraction time averaged 16 min/level. Baseline SSEPs were unreliable in 3 due to comorbidities in 2 and anesthesia in 1; one of those resulted in transient quadriceps weakness, fully recovered at 6 weeks. In 25/56, no saphSSEP changes occurred, and none had postoperative femoral nerve deficits. In 24/31 with saphSSEP changes, responses recovered intraoperatively following intervention, with normal postoperative function in all but one with delayed quadriceps weakness, improved at 4 months and recovered at 9 months, and a second with transient isolated anterior thigh numbness. In the remaining 7/31, saphSSEP changes persisted to close, and resulted in 2 transient isolated anterior thigh numbness and 2 combined sensory and motor femoral nerve deficits, both resolved at between 4 and 8 months.


SaphSSEP was reliably monitored in most cases and provided actionable feedback that was highly predictive of neurological events during LIF.

Level of evidence

Diagnostic: individual cross-sectional studies with consistently applied reference standard and blinding.

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Correspondence to Antoine Tohmeh.

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A. Tohmeh is a consultant for Alphatec Spine, the manufacturer of the device used in this study, but received no financial support or remuneration related to the publication of this article. C. Somers has no conflicts. K. Howell is an employee of Alphatec Spine. All authors have full control of the primary data and allow the journal to review the data if requested.

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Tohmeh, A., Somers, C. & Howell, K. Saphenous somatosensory-evoked potentials monitoring of femoral nerve health during prone transpsoas lateral lumbar interbody fusion. Eur Spine J 31, 1658–1666 (2022).

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  • LLIF
  • PTP
  • Lumbar plexus
  • Femoral nerve
  • Quadriceps palsy