Positional changes in intraoperative EMG recordings with the prone transpsoas approach to the L4-5 disc space

Introduction: Accessing the L4-5 disc space through the prone transpsoas approach (PTP) is difficult due to the more anterior positioning of the lumbar plexus across the lateral disc space. In this study, the effects of patient positioning on electromyography (EMG) recordings were investigated.

Methods: Single-level PTP at L4-5 was performed on 10 patients who had EMG values recorded anteriorly and posteriorly on top of the psoas muscle as well as at the level of the disc space. EMG recordings were evaluated with the bed at a neutral position and as well as with the operating table rotated 30 degrees away from the surgeon.

Results: All 10 patients demonstrated significantly improved EMG values at all points after table rotation. Before table rotation, the posterior EMG values were in the risk zone ( < 6 mA) for 7 of 10 patients when measured on top of the psoas and for 5 of 10 patients when measured at the level of the disc space. After the table rotation, no patients had posterior EMG recordings in the risk zone. Similarly, all anterior EMG recordings demonstrated improvement after table rotation.

Conclusion : Intraoperative EMG recordings were more favorable with table rotation than in the typical neutral position. Given the known higher risk of femoral nerve injury at L4-5, rotating the table away from the surgeon 30 degrees when docking with the initial dilator and retractor can allow for safer positioning of the retractor relative to the lumbar plexus.