Tag: Femoral nerve

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

Operative Neurosurgery 30:566–570, 2026

This single-institution retrospective study evaluates whether low posterior electromyography (EMG) stimulation thresholds during lateral L4-5 lumbar interbody fusion (LLIF) correlate with postoperative femoral nerve motor or sensory neurapraxia. Forty-two lateral-position single-level L4-5 LLIFs with neuromonitoring data showed no significant association between posterior EMG threshold or retractor time and transient postoperative anterior thigh numbness or weakness.

The cohort experienced transient sensory neurapraxia in 38% at six weeks that resolved by six months; only one patient had temporary motor neurapraxia. Limitations include small sample size, retrospective design, and short follow-up, leading authors to conclude no demonstrable link between posterior EMG threshold and plexus injury in this series.

Context: In L4-5 transpsoas LLIF, the retractor is placed near the lumbar plexus; directional EMG stimulation thresholds are used intraoperatively to estimate nerve proximity and potentially reduce injury risk.

Objective: Assessed whether posterior EMG stimulation threshold was associated with lumbar plexus injury/neurapraxia after single-level L4-5 LLIF performed in the lateral position.

Design/criteria: Retrospective, single-institution review of single-level L4-5 LLIF (Jan 2019–May 2022) with available neuromonitoring thresholds and retractor time; excluded cases with additional levels or missing monitoring data.

Cohort/intraop metrics: 42 patients (mean age 66 years); mean retractor time 12.4 minutes; mean posterior EMG threshold 10.4 mA.

Neurologic outcomes: Femoral motor neurapraxia occurred in 1 patient (2%); sensory neurapraxia (anterior thigh numbness) occurred in 16 patients (38%) at 6 weeks and resolved to 0% by 6 months.

Main finding: Posterior EMG threshold was not associated with postoperative motor neurapraxia or sensory neurapraxia at 6 weeks (including logistic regression showing OR 1.00; P=.98 for thigh numbness).

Other associations: No significant correlation between posterior EMG threshold and retractor time (Spearman ρ=0.11; P=.50) or postoperative ODI (ρ=0.17; P=.33).

Notable case/interpretation: The single motor neurapraxia case had 27-minute retractor time with posterior EMG 5 mA and recovered by 6 months; median retractor time in the cohort was low (10.8 minutes), limiting conclusions about longer retraction durations.

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Variations of the extrapsoas course of the lumbar plexus with implications for the lateral transpsoas approach to the lumbar spine: a cadaveric study

Acta Neurochirurgica (2024) 166:319

Together with an increased interest in minimally invasive lateral transpsoas approach to the lumbar spine goes a demand for detailed anatomical descriptions of the lumbar plexus. Although definitions of safe zones and essential descriptions of topographical anatomy have been presented in several studies, the existing literature expects standard appearance of the neural structures. Therefore, the aim of this study was to investigate the variability of the extrapsoas portion of the lumbar plexus in regard to the lateral transpsoas approach.

Methods A total of 260 lumbar regions from embalmed cadavers were utilized in this study. The specimens were dissected as per protocol and all nerves from the lumbar plexus were morphologically evaluated.

Results The most common variation of the iliohypogastric and ilioinguinal nerves was fusion of these two nerves (9.6%). Nearly in the half of the cases (48.1%) the genitofemoral nerve left the psoas major muscle already divided into the femoral and genital branches. The lateral femoral cutaneous nerve was the least variable one as it resembled its normal morphology in 95.0% of cases. Regarding the variant origins of the femoral nerve, there was a low formation outside the psoas major muscle in 3.8% of cases. The obturator nerve was not variable at its emergence point but frequently branched (40.4%) before entering the obturator canal. In addition to the proper femoral and obturator nerves, accessory nerves were present in 12.3% and 9.2% of cases, respectively.

Conclusion Nerves of the lumbar plexus frequently show atypical anatomy outside the psoas major muscle. The presented study provides a compendious information source of the possibly encountered neural variations during retroperitoneal access to different segments of the lumbar spine.

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