Study on variant anatomy of sciatic nerve

Abstract

Introduction: Sciatic Nerve (SN) is the nerve of the posterior compartment of thigh formed in the pelvis from the ventral rami of the L4 to S3 spinal nerves. It leaves the pelvis via the greater sciatic foramen below piriformis and divides into Common Peroneal Nerve (CPN) and Tibial Nerve (TN) at the level of the upper angle of the popliteal fossa. Higher division of the sciatic nerve is the most common variation where the TN and CPN may leave the pelvis through different routes. Such variation may lead to compression of the nerve and lead to Non-discogenic sciatica.

Materials and methods: Fifty lower limbs were used for the study from Department of Anatomy, J.J.M.M.C Davangere, Karnataka, India.

Observation and results: In our study on 25 cadavers (50 lower limbs), we have observed 4 (8 %) lower limbs high division of sciatic nerve was noted. High division of sciatic nerve in the back of thigh was noted in one specimen (2%), while high division within the pelvis was noted in 3 specimens (6%), while in 46 (92%) it occurred outside the pelvis.

Conclusion: Knowledge regarding such variation and differences in the course of SN is important for the surgeons to plan for various surgical interventions pertaining to the gluteal region. The variant anatomy of SN may cause piriformis syndrome and failure of SN block. Hence present study is undertaken to know the level of division, exit, course, relationship to piriformis and variations in the branching pattern of SN.

Keywords: Common peroneal nerve; Piriformis; Tibial nerve.

Figures

[Table/Fig-1]:

Showing higher division of SN on the right side into TN & CPN which later united in the middle third of thigh and further showing trifurcation of SN in its terminal part in to TN nerve, CPN and nerve to soleus on the right side

[Table/Fig-2]:

Showing trifurcation of SN into TN nerve, CPN and nerve to soleus on the left side

[Table/Fig-3]:

Showing undivided left sided sciatic nerve emerging beneath lower border of piriformis muscle later dividing beneath the lower border of muscle in the back of thigh into TN nerve & CPN respectively

[Table/Fig-4]:

Showing higher division of SN into TN nerve which passes below while CPN nerve passes through piriformis on the right side

[Table/Fig-5]:

Showing higher division of SN into TN nerve passing below while CPN nerve passing above piriformis on the left side