A rare lumbosacral trunk variation: communicating branches to the femoral and obturator nerves

This report presents a case of bilateral lumbosacral trunk (LST) variation observed during cadaveric dissection and to analyze its possible developmental mechanism and clinical significance.

During the dissection of a Chinese adult male specimen, bilateral variations of the LST were observed, with communicating branches joining the femoral nerve and/or obturator nerve.

The right LST was formed solely by the ventral ramus of the fifth lumbar nerve (L5), without contribution from the fourth lumbar nerve (L4), and gave off one communicating branch (1.46 mm in diameter) joining the femoral nerve. The left LST was formed by the ventral rami of L4 and L5 and gave off two communicating branches joining the femoral nerve and obturator nerve, respectively.

This study reports a rare form of LST variation, in which both sides gave off one or two communicating branches to other nerves. This variation has significant clinical importance, as compression of the L5 nerve root may produce clinical presentations that do not match standard anatomical expectations. In addition to typical sciatica, atypical symptoms such as pain and sensory abnormalities in the groin area and anteromedial thigh may occur. Clinicians should be aware of such variations, especially when patient symptoms are inconsistent with imaging findings, and should consider possible neuroanatomical variations. This finding provides new anatomical evidence for understanding the complexity of nerve distribution in the lumbosacral region and for improving the diagnosis and treatment of related disorders.