European Journal of Cardiovascular Medicine

Sciatic nerve is the thickest nerve in the body. It is the largest branch of sacral plexus with the root value L4, L5, S1, S2, S3. It extends from the pelvis where it is located in front of the piriformis to the upper angle of popliteal fossa which is at the level of the junction of lower and middle thirds of the thigh, where it divides into tibial and common peroneal nerves. Normally, the sciatic nerve enters the gluteal region through the greater sciatic foramen below the piriformis. Intra-pelvic division of the sciatic nerve is a variation. Sometimes, there is higher division of the sciatic nerve in the gluteal region or in the thigh. Lower division of the sciatic nerve is also found.

The sciatic nerve divides into the tibial and common nerves at the upper angle of the popliteal fossa. Intra pelvic division of sciatic nerve is encountered in a few people. In such cases, two types of exits from pelvis are found.

Type 1: Common peroneal nerve penetrating the piriformis and tibial nerve passing below the piriformis.

Type 2: Common peroneal nerve passing above the piriformis and tibial nerve passing below the piriformis.

Level of division in the thigh, above the level of superior angle of the popliteal fossa, is encountered in several specimens.In some cases, division of sciatic nerve was recorded at the level of ischial tuberosity.In such cases undivided sciatic nerve passes below the piriformis and divides just below the ischial tuberosity. In some other cases just before reaching the popliteal fossa, division occurs. Lower division of sciatic nerve is found in 12 cases

T Cadavers, Ruler, Forceps, Gloves.

Variation from the normal level of division is measured using a ruler.

40 lower limb specimens are used for this study. Out of the 40 specimens studied, 19 cases showed higher division of the sciatic nerve (47.5%). Lower division of sciatic nerve is found in 12 cases (30%). Normal division of sciatic nerve is found in 9 cases (22.5%).

Table 1. Level of division

Previous studies on sciatic nerve division primarily focus on anatomical variations in the location where the sciatic nerve splits into tibial and common peroneal branches, often examining cadavers to determine the frequency of high division within the pelvis; at different levels in the thigh, with implications for conditions like piriformis syndrome, potentially causing complications during injecting local/regional anesthetics to block the nerve and during surgical procedures.

Magnitude of the variation: Globally – According to Beaton and Anson [1,2] 90% shows normal anatomy. In4% division occurs between and below piriformis. In another 4% one division above and the other division below piriformis; and in2 %( 1specimen; because studied 50 specimens) common peroneal nerve and tibial nerve branched directly from the lumbosacral plexus. The common peroneal neve pierced the piriformis and tibial nerve emerged under the piriformis.

According to Beaton and Anson, there are 6 types of variations of the relationship between piriformis and exit of sciatic nerve from the pelvis.

Type 1: An undivided nerve comes out below the piriformis.

Type 2: Common peroneal nerve penetrating the piriformis and tibial nerve emerging below the piriformis.

Type 3: Common peroneal nerve passing above the piriformis and tibial nerve passing below the piriformis.

Type 4: Undivided sciatic nerve passing through the piriformis.

Type 5: The common peroneal nerve passing above the piriformis and tibial nerve penetrating the piriformis.

Type 6: Undivided sciatic nerve passes above the piriformis.

In India (Maharashtra) – According to Guvencer et al [3] in 48% cases sciatic nerve divides in the gluteal region. They examined variations in the sciatic nerve, finding a high division rate in a sufficient portion of the cadavers with some cases showing the nerve dividing within the pelvis. They have examined 50 gluteal regions in 25 cadavers and observed that in 40% of specimens, sciatic nerve has been dividing in the gluteal region.

In Tamil Nadu- According to AnbumaniT.L. [4], in 82% normal anatomy of sciatic nerve and piriformis muscle and 18% showed variations. 4%showed unilateral and 16%showed bilateral variations.

Ugrenovic et al 2005 (5) have found high division of sciatic nerve in 27.5% specimens in a study performed in 100 foetuses.

Machado et al 2003 (6) have performed a dissection in 100 foetuses and have reported 3 types of variations.

a.      Common peroneal nerve penetrating the piriformis and tibial nerve passing under the piriformis.

b.      Common peroneal nerve passing above the piriformis and tibial nerve passing below the piriformis.

c.      Sciatic nerve piercing piriformis.

The present study examined variations in the sciatic nerve division, finding a high division rate in a significant portion of cadavers, with some cases showing lower division also, all coming under the type 1 pattern of nerve exit. We have examined 40 lower limbs and observed that in 19 specimens, sciatic nerve has been dividing at a higher level (figure.1); and in 12 specimens, sciatic nerve has been dividing at a lower level(figure.2). In the remaining specimens, normal division has been observed(figure.3). The observations are tabulated in Table 1.

The knowledge regarding the level of division of sciatic nerve and its exit from the pelvis is of great clinical importance. Abnormal course and division may lead to sciatic neuropathy. The most prevalent level of bifurcation of the sciatic nerve in the present study is the higher division of the sciatic nerve. During posterior hip operations, this may create unexpected complications. High division can also cause sciatica, piriformis syndrome, and may lead to a failed sciatic nerve block. Thus this study proves to be important in the field of Anatomy, Orthopedics, Surgery, Anesthesia and Research.

1.      Beaton LE, Anson BJ. The relation of the sciatic nerve and its subdivisions to the piriformis muscle. Anat Rec 1937;70:1-5.

2.      Beaton LE. The sciatic nerve and piriform muscle: Their interrelation a possible cause coccgoynia. J Bone Joint Surgery Am 1938: 20:686-688.

3.      Guvencer M, Iyem C,Akyer P,Tetik S, Naderi S. Variations in the High Division of the Sciatic Nerve and Relationship Between the Sciatic Nerve and the Piriformis. Turkish Neurosurgery 2009; 19 (2):139-144.

4.      Anbumani TL, Thamarai Selvi A, Anthony Ammal S. Sciatic nerve and its Variations: An Anatomical Study. Int.J Anat Res 2015: 3 (2:1121-1127).

5.      Ugeronovic S, Javanovic I, Krstic V, Stojanovic V, Vasovic L, Antic S, Pavilovic S. The level of the sciatic nerve division and its relations to the piriform muscle. Vogno Sanit Pregl.2005; 62 (1) 45 – 49.

6.      Machado FA , Babinski M A, Brasil F B, Favorito L A, Abidu-Figureiedo M, Costa M G. Anatomical variations between sciatic nerve and piriform muscle during fetal period in human. Int  J Morphol 2003;21(1):29-35. HW.

7.      Moore KL, Dalley AF. Clinical Oriented Anatomy, 4^th edition, Baltimore Lippincott Williams and Wilkins, 1999, 558.

8.      Dutta AK, Gluteal region. In: Essentials of human anatomy, Superior and Inferior Extremities 2009: 4^th ed. Kolkata Current Books International: 188 - 89.

9.      Kirschner JS, Foye PM, Cole JL. Piriformis syndrome, diagnosis and treatment. Muscle Nerve 2009; 40(1:10-8).

10.   Nayak S. An unusual case of trifurcation of the sciatic nerve. Neuroanatomy 2008;5:6-7.

11.   Prakash, Bhardwaj AK, Devi MN, Sridevi NS, Rao PK Singh G. Variations in the high division of the sciatic nerve and relationship between the sciatic nerve and the piriformis. Singapore Med J 2010;51(9:721).

12.   Bergman RA, Afifi AK, Miyauchi R. Compendium of human anatomical variations 1988.

13.   Demiryurek D, Bayramoglu A, Enbil M, Aldur MM, Mustafa ES. Bilateral divided piriformis muscles together with the high division of the sciatic nerve. Gazi Med J 2002; 13:41-4.

14.   Shewale AD, RR Karambalekar, BN Umarji, Study of variations in the divisions, course and termination of the sciatic nerve. JKIMSU 2013; 2(1):62-68.

15.   Pecina M. Contribution to the etiological explanation of the piriformis syndrome. Acta Anat (Basal) 1979;105:181-187.

16.   Pokorny D, Jahoda D, Veigl D, Pinskerova V, Sonsa A. Topographic variations of the relationship of the sciatic nerve and the piriformis muscle and its relevance to the palsy after total hip anthroplasty. Surge Radiol Anat 2006;28:88-91.

17.   Chiba S, Multiple positional relationships of nerves arising from the sacral plexus to the piriformis muscle in humans. Kaibogaku Zasshi 1992; 67 (6); 691-724.

18.   Babinski MA, Machado FA, Costa WS. A rare variation in the high division of the sciatic nerve surround the superior gemellus muscle. Eur J of Morphol 2003; 41(1):41-42.

19.   Sayson SC, Ducey JP, Maybrey JB, Wesley RL, Vermilion D, Sciatic entrapment neuropathy associated with an anomalous piriformis muscle pain 1994; 59: 149-152.

20.   Ozaki S, Hamabe T, Muro T. Piriformis syndrome resulting from an anomalous relationship between the sciatic nerve and the piriformis muscle. Orthopedics 1999; 22 (8): 771-772