Posterior femoral cutaneous nerve
The posterior femoral cutaneous nerve originates from the main nerves and/or the roots of the sacral plexus including the inferior gluteal, common peroneal, and tibial nerves. It leaves the pelvic cavity passing posterior through the greater sciatic foramen inferior to the piriformis (infrapiriform canal), along with the pudendal and inferior gluteal nerves medial to it and the sciatic nerve lateral to it. The inferior gluteal vein emerges from the inferior aspects of the piriformis’s insertion on the sacrum to also passes through the greater sciatic foramen in the infrapiriform canal.
The piriformis fascia is thickened at its superior and inferior end filling the gaps between its related structures (Nutter 1936): (i) at the upper boarder of the piriformis where it is contiguous with the lower edges of the gluteus medius and minimus. (ii) At the lower boarder of the piriformis, in the space between the piriformis and superior gemellus, immediately lateral to the sciatic nerve. The thickening of the fascia at these levels can create definitive bands that can act as a potential source of nerve entrapment involving the superior gluteal nerve superiorly, or, the sciatic, posterior femoral cutaneous or inferior gluteal nerve inferiorly.
Compression of the inferior gluteal vein from a hypertrophied piriformis causes varicosities that the posterior femoral cutaneous nerve stretches over causing a compression of the nerve (Williams et al 2020). This ‘crowding effect’ from the piriformis muscle above, the greater sciatic notch behind and the inferior gluteal vessels and nodes below may also compress the inferior gluteal nerve (LaBan et al 1982). A varicosity of the inferior gluteal vein may explain the prevalence of posterior femoral cutaneous nerve involvement in piriformis syndrome whereby a direct compression from the piriformis would normally affect the larger sciatic nerve (Williams et al 2020) by compressing it against the superior aspect of the ischial spine (Goidescu et al 2022 & Hanna et al 2024).
The posterior femoral cutaneous nerve, after passing inferior to the piriformis in the infrapiriform canal, then descends posterior to the superior gemellus, obturator internus, inferior gemellus and quadratus femoris, staying lateral to the ischial tuberosity and medial to the the sciatic nerve, to the lower boarder of the gluteus maximus.
The gluteus maximus, as it covers the ischial tuberosity, sends fascial expansions to the lateral and medial aspects of the ischial tuberosity to form a retinaculum. Laterally, this fascial expansion splits to form a canal that surrounds, and embeds, the posterior femoral cutaneous (and sciatic) nerve. The retinaculum receives contributions from the biceps femoris to anchor the sacrotuberous ligament and hamstrings (< long head of biceps femoris). Therefore the gluteus maximus establishes a synergy with (i) the biceps femoris through this retinaculum (Perez-Bellmunt et al 2015), (ii) with the obturator internus/urogenital diaphragm and the levator ani through fascial septa (Siess et al 2023) and (iii) with the thoracolumbar fascia and erector spinae aponeurosis through shared attachment sites (Willard et al 2012). As the posterior femoral cutaneous (and sciatic) nerves pass lateral to the ischial tuberosity they can become scarred onto the lateral border of the hamstring tendons in cases of chronic hamstring tendonopathy (Remy et al 2022).
At the lower boarder of the gluteus maximus the posterior femoral cutaneous nerve gives off three branches (Jiamjunyasiri et al 2023):
Thigh branches pass down the posterior surface of the thigh deep to the fascia lata being distributed to the skin and fascia of the posterior thigh and proximal leg. The perineal branches (refer ’perineal branches’) forms the medial branch of the thigh branch and is distributed to the superomedial region of the posterior thigh. Thigh branches originating from the inferior gluteal and common peroneal nerve are distributed more laterally, whereas thigh branches originating from the tibial nerve are distributed more medially.
Gluteal branches (inferior cluneal nerve, lateral branch) are distributed in the inferior half of the gluteal region. These branches run lateral to the ischial tuberosity beneath the gluteus maximus and recur at the inferior margin of the muscle. The posterior femoral cutaneous nerve is mainly distributed in the inferior gluteal region. The gluteal branches originate from the inferior gluteal, common peroneal and tibial nerves and are radially distributed. Branches originating from inferior gluteal and common peronal nerves are distributed more laterally whereas those originating from the tibial nerve are distributed more medially.
When present the perforating cutaneous nerve or the perforating STL nerve innervates the inferomedial buttock or perineum respectively. Branches originating from the pudendal nerve and/or the roots of the pudendal nerve (S2-4 ventral rami) give rise to the perforating of the STL nerve, and branches from the S2-3 ventral rami give rise to the perforating cutaneous nerve. The perforating STL nerve, and, sometimes, the perforating cutaneous nerve, perforate the sacrotuberous ligament to run medial to the ischial tuberosity, distinct from the posterior femoral cutaneous nerve that runs lateral to it. When the perforating cutaneous nerve is absent branches from the posterior femoral cutaneous nerve (gluteal branch) innervate the same dermatomal regions in the inferomedial buttock to form the inferior cluneal nerves (medial branch) (Shafarenko et al 2023).
Perineal branches. These branches originate from tibial > pudendal nerve. The perineal branch runs along the lateral surface of the ischial tuberosity to then turn medially at the ischial tuberosity. It branches into the upper medial part of the thigh (refer ’thigh branches’) to innervate the superomedial region of the posterior thigh, and the lateral part of the perineum to supply the skin of the scrotum or labium majus and the root of the penis or clitoris. Sometimes the perineal branch communicates with a branch of the pudendal nerve in the perineum.
Aside from the posterior femoral nerve cutaneous innervation to the buttocks and perineum can come from:
Branches from the S4 or S5 dorsal rami penetrate the proximal part of the sacrotuberous ligament, and then either penetrate the gluteus maximus or curl around its inferior margin to be distributed to the inferomedial gluteal region (Jiamjunyasiri et al 2023).
Branches from the pudendal nerve can be distributed to the medial part of the inferior gluteal region (Jiamjunyasiri et al 2023).
A branch originating from the inferior gluteal nerve penetrates the gluteus maximus to be distributed to the lateral part of the inferior gluteal region (Jiamjunyasiri et al 2023).
The superior gluteal nerve (and vessels) pass through the greater sciatic foramen superior to the piriformis (suprapiriform canal). Branches from the superior gluteal nerve then penetrate the tensor fascia lata and gluteus maximus to be distributed in areas surrounded by regions of innervation from the iliohypogastric, inferior cluneal, superior cluneal, and lateral femoral cutaneous nerves (Jiamjunyasiri et al 2023).
The perforating STL nerve originates from the pudendal nerve or the root of the pudendal nerve in the area surrounding the ischial spine, and the perforating cutaneous nerve originates from the ventral rami of S2-3. These nerves perforate the sacrotuberous ligament (variably so in the case of the perforating cutaneous nerve) to run medial to the ischial tuberosity to supply the perineum (perforating STL nerve) and inferomedial gluteal region (perforating cutaneous nerve). When the perforating cutaneous nerve is absent a branch from the posterior femoral cutaneous nerve (gluteal branch) forms the inferior cluneal nerve (medial branch) supplying the same dematomal distribution in the inferomedial gluteal region (Shafrenko et al 2023).
References
Jiamjunyasiri A, Tsutsumi M, Muro S, Akita K. (2023). Origin, course, and distribution of the posterior femoral cutaneous nerve and the spatial relationship among its branches
Shafarenko K, Walocha JA, Tubbs RS, Jankowska K, Mazurek A. (2023). Anatomical description of the perforating cutaneous nerve.
Williams SE, Swetenburg J, Blackwell TA, Reynolds Z, Black AC Jr. (2020). Posterior femoral cutaneous neuropathy in piriformis syndrome: A vascular hypothesis.
LaBan MM, Meerschaert JR, Taylor RS. (1982). Electromyographic evidence of inferior gluteal nerve compromise: an early representation of recurrent colorectal carcinoma.
Pérez-Bellmunt A, Miguel-Pérez M, Brugué MB, Cabús JB, Casals M, Martinoli C, Kuisma R. (2015). An anatomical and histological study of the structures surrounding the proximal attachment of the hamstring muscles
Siess M, Steinke H, Zwirner J, Hammer N. (2023). On a potential morpho-mechanical link between the gluteus maximus muscle and pelvic floor tissues.
Willard FH, Vleeming A, Schuenke MD, Danneels L, Schleip R. (2012). The thoracolumbar fascia: anatomy, function and clinical considerations.
Remy LF, Imbergamo C, Parks BG, Gould HP, Dreese JC. (2022). The Posterior Femoral Cutaneous Nerve and Branches are in Proximity to the Surgical Approach During Proximal Hamstring Repair
Goidescu O, Enyedi M, Tulin A, Tulin R, Vacaroiu I, Nica A, Dragos D, Ionescu D, Georgescu D, Miron A, Filipoiu F (2022). Overview of the anatomical basis of the piriformis syndrome-dissection with magnetic resonance correlation
Hanna AS, Staniszewski TM, Omar AH, Guevara-Moriones N, Moscote-Salazar LR, Hilger KH, Hellebrand DJ. (2024). Anatomical Relationships of the Sciatic Nerve and Pudendal Nerve to the Ischial Spine as they Exit the Greater Sciatic Foramen.
Nutter JA. (1936). A Clinical and Anatomical Study of Sciatica.