Anatomical variations of lumbosacral plexus

Deviations detected during spinal operations have motivated us to start research related to variations of lumbosacral plexus formation. Aim of this work was to find out deviations of its formation from ascension of particular roots from foramen invertebrale and foramina sacralia up to formation of terminal branches.

One hundred lumbosacral plexi have been examined in 50 adult cadavers for a purpose to find out an incidence of neural variations. We have observed participation of Th₁₂ root, L₄ and L₅ roots in its formation, as well as various deviations from ascension of particular plexiform roots up to their ending branches. For lumbal plexus, we have observed four nerve roots and six lumbal nerves; for sacral one, three sacral roots with a share of S₄ and lumbosacral trunk formed of L₄ and L₅ roots and four sacral nerves. We have considered also their course, anastomoses and thickness. We highlight motoric innervation particularities in relation to diagnostics besides anatomical complexity and variability.

Variations on the level of neural roots were common, nerve formations were uncommon. Thickness of neural roots, formation or their absence were dependent on the type of plexus, particularly in sacral area. For lumbal plexus, L₁ root was the thinnest and L₄ root was the thickest. L₃ root was the thickest in six cases. Fifth lumbal root usually completely filled foramen invertebrale. We have observed double ascension of L₄ root from foramen invertebrale in 25 cases and plexiform in five cases. In other cases it was branched in various distance following ascension from foramen invertebrale. Plexiform ascension of L₃ root along with L₄ root was present in two cases. Double ascension of L₃ root was present in four cases. L₂, L₃ along with L₅ roots were doubled in two cases. Iliohypogastric nerve was the longest, ilioinguinal was the thinnest and nervus femoralis was the thickest. Changes in sacral plexus on the level of neural roots have been observed 41-times. Double ascension of L₅ root was present in eight cases and plexiform in four cases. Double S₁ root at ascension from foramina sacralia was present 16 times, S₂ 8 times, S₃ once and S₁ along with S₂ 4 times. S₁, S₂ and S₃ roots were branched in various distance following ascension from foramina sacralia in 15 cases. Truncus lumbosacralis was thickened in 19 cases, a share from L₄ root was thicker as L₅ root in 11 cases. Low level of connection between truncus lumbosacralis and S₁ root was observed in 10 cases. Nervus ischiadicus has branched into tibial and peroneal portions already in minor pelvis in two cases. The level of distance of n. (nervus) gluteus superior, n. gluteus inferior, n. cutaneus femoris posterior and n. pudendus was dependent on the plexus type.

This study enabled us to find out and to describe extraordinary anatomical deviations in formation of neural roots and nerves of lumbal and sacral plexus, undescribed yet.