This the sacral segment of the lumbosacral plexus and it is inferiorly positioned when compared to the lumbosacral plexus.It lies on the Piriformis muscle in the posterior aspect of the Pelvic floor. The Hypogastric vessels and Ureter as well as the Pelvic colon are placed anteriorly to the Sacral plexus. A Sacral plexus is formed by anterior root of the spinal segment L4, L5, S1, S2 and S3. Each of these roots divide into anterior and posterior divisions; such that all posterior divisions L4 to S2 will unite to form common Peroneal nerve.
All the anterior divisions will unite to form the Tibial nerve. Normally, the Tibial nerve is bigger than the common Peroneal nerve. At a distance around the distal half of the thigh in about 60% of cases the common Peroneal nerve fuses with the Tibial nerve to link the Sciatic nerve- this is by the biggest nerve in the body. The posterior division of L4, L5, and S1 each sends out a nerve twig that unite to form the Superior Gluteal nerve that is distributed after, it passes above the Piriformis muscles through the greater Sciatic foramen to innervate the Gluteus medius, Gluteus minimus and the Tensor Fascia Latae muscles. Each of L4, L5, S1 and S2 will send out a nerve twig from their posterior division to form the inferior Gluteal nerve which supplies the Gluteus maximus muscle (mostly the inferior gluteal nerve is from L5, S1, S2).
Posterior Cutaneous nerve of the thigh is formed by the union of the nerve twig from the posterior division of L5, S1 and also form both the anterior and posterior division of S2.
Nerve to Quadratus Femoris is formed by union of nerve twigs from anterior divisions of L4, L5, S1.
Nerve to Obturator Internus and Superior Gemellus is formed by nerve twigs from anterior divisions of L5, S1, S2. From the posterior division of S2 and anterior division of S3 we have Perforation nerve of thigh while the anterior division of S2 and posterior division of S3, we have Pudendal nerve.
