• Carlo Mandelli, Elena Virginia Colombo, Giovanni Marco Sicuri, and Pietro Mortini.
• Department of Neurosurgery, Vita-Salute San Raffaele University, IRCCS San Raffaele Scientific Institute, Via Olgettina 60, 20132, Milan, Italy. mandelli.carlo@hsr.it.
• Eur Spine J. 2016 Dec 1; 25 (12): 4155-4163.

PurposeXLIF ® is a widely used minimally invasive technique to treat different spine pathologies. The aim of this study was to quantify nerve distortion of lumbar plexus during XLIF ® approach and to correlate it with morphometric data.MethodsNine fresh frozen cadaveric specimens were used. All specimens were subjected to the same dissection procedure cored on a left XLIF® approach at L2/L3 and L4/L5 levels. Distortion of cutaneous superficial nerves, femoral nerve (FN) at L4/L5 and genitofemoral nerve (GN) at L2/L3 and L4/L5 while opening the retractor were assessed and analyzed with respect to psoas muscle features.ResultsSuperficial nerves were slightly displaced but never stretched. FN, as well as GN at L4/L5 level, could be displaced and stretched by the blades. Statistically significant correlation between FN distortion and the amount of psoas fibers interposed between the posterior blade of the retractor and the nerve itself (TCK) was found. GN distortion was found to be related to its clock position on an axial section of psoas muscle seen from cranially at L4/L5.ConclusionFN was in close connection with the deep psoas muscle fibers and it is subjected to anterior translation that correlates with TCK. This mechanism may partly explain the rate of femoral nerve palsy that occurs despite neuromonitoring and safe entry zones respect. The GN location at L4/L5 should be considered not only for its projection in Zone I, but also for its clock position on the psoas muscle surface, since it affects its distortion.

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