Indian Journal of Basic and Applied Medical Research; June 2015: Vol.-4, Issue- 3, P. 34-44

Original article

A Study on the bifurcation of sciatic nerve with its clinical significance 1Dr.

Satyajit Sangram , 2Dr. Chiranjit Samanta , 3Dr. Mithu Paul , 4Dr. Susumna Biswas , 5Dr. Reshma

Ghosh , 6Dr. Amitava Sarkar , 7Dr. Saktipada Pradhan , 8 Prof. (Dr.) Sudeshna Majumdar

1,2,3,5,6,7 4

Junior Resident, Department of Anatomy,Nilratan Sircar Medical College, Kolkata – 700014, West Bengal, India

Demonstrator, Department of Anatomy, Nilratan Sircar Medical College, Kolkata – 700014, West Bengal, India.

8 Professor,

Department of Anatomy, Nilratan Sircar Medical College, Kolkata -700014, West Bengal, India.

Corresponding author: Dr. Sudeshna Majumdar

Abstract: Introduction: The sciatic nerve (SN) arises from the sacral plexus. It usually appears in the gluteal region below the piriformis muscle, passes along the back of the thigh and divides into tibial and the common fibular (peroneal) nerves near the apex of the popliteal fossa. But the point of bifurcation of the sciatic nerve is very much variable. Methods: A study was conducted on the division of the sciatic nerve, in the Department of Anatomy, NRS Medical College, Kolkata, over two years, from December, 2012 to the November, 2014. 50 inferior extremities of 25 cadavers were dissected for this study. The dissections were done while teaching MBBS Students in the said department. The relevant structures were observed minutely and photographs were taken. Observations: Among the fifty inferior extremities, in the sciatic nerve was found to be divided into tibial and common peroneal nerves in different levels (in the pelvis, gluteal region etc.) Results: Out of fifty lower limbs, in forty one cases (82%) the sciatic nerve divided in the back of the thigh, near the apex of the popliteal fossa according to normal anatomy. In nine lower limbs (18% cases), the nerve divided high above, either in the sacral fossa (14% cases) or in the gluteal region (4% cases). Conclusion: This high division of the sciatic nerve may result in nerve injury during deep intramuscular injections in the gluteal region, sciatica, piriformis syndrome etc. So this variation has importance in gross and clinical anatomy. Key Words: Division of Sciatic Nerve, tibial nerve, common peroneal nerve, piriformis muscle

Introduction

nerve leaves the pelvis via the greater sciatic

Sciatic is a Greek word derived from ‘ischiadicus’.

foramen, below the piriformis and above the superior

Sciatic nerve is also known as ischiadic nerve or

gemellus muscle, descends in the gluteal region

ischiatic nerve, is a large nerve in humans and other

between

animals1. Sciatic nerve (SN) is the nerve of the

tuberosities. Then it runs along the back of the thigh

posterior compartment of the thigh and via its major

dividing into tibial and the common peroneal

branches of all the compartments of leg and foot. It is

(fibular) nerves at a varying level proximal to the

typically 2cm. wide at its origin and is the thickest

knee joint. The point of bifurcation of the sciatic

nerve in the human body with the root value: L4, 5,

nerve is very much variable 2. The common site is at

S1-3. Formed in the pelvis from the ventral rami of

the junction of the middle third and lower third of the

fouth lumbar to third sacral spinal nerves, the sciatic

back of the thigh, near the apex of the popliteal fossa

the

greater

trochanter

and

ischial

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Indian Journal of Basic and Applied Medical Research; June 2015: Vol.-4, Issue- 3, P. 34-44

(85-89% cases), but division may occur at any point 1, 2

Materials and methods

. The

A study was undertaken to detect different variations

tibial and common proneal nerves are structurally

in the bifurcation of sciatic nerve, in the Department

separate and only loosely held together within the

of Anatomy, NRS Medical College, Kolkata, over

sciatic nerve. Dorsal divisions of ventral rami of L4-5,

two years, from December, 2012 to the November,

S1-2 form the common peroneal component and the

2014. 50 inferior extremities of 25 cadavers were

ventral divisions of ventral rami of L4-5, S1-3 form the

dissected minutely for this study while teaching

above this and rarely may occur below it

2

tibial component of the sciatic nerve . Very often

MBBS Students. The cadavers belonged to the adult

these two nerves arise separately from the sacral

age group (within 50 to 70 years age group); twenty

plexus and at that time, the common peroneal nerve

male and five female cadavers were included in this

may pass through the piriformis muscle and the tibial

study.

2

nerve below the muscle .

The relevant structures were observed carefully and

The piriformis is a flat muscle, pyramidal in shape,

photographs were taken. Variations were noted with

lying below the posterior margin of the gluteus

calculation of their percentage.

medius. It arises from the front of the sacrum by three

Observations

fleshy digitations and partly from the greater sciatic

Among the fifty inferior extremities, in twenty-five

foramen and sacrotuberous ligament. The muscle

cadavers, the sciatic nerve was found to be divided

comes out of the pelvis through the greater sciatic

into tibial and common peroneal nerves in different

foramen and is inserted by a rounded tendon to the

levels (in the pelvic cavity, gluteal region etc.).

upper border of the greater trochanter of femur2.

In forty one cases the sciatic nerve divided in the

Piriformis syndrome is a controversial condition in

lower part of the back of the thigh, near the apex of

which the anomalous relationship between piriformis

the popliteal fossa, according to normal anatomy. So

and sciatic nerve is thought to cause pain in buttocks

in 82% cases the nerve was found to be bifurcated in

2

and along the course of the sciatic nerve . Piriformis

the posterior compartment of the thigh above the

syndrome may be caused by an entrapment of the

knee joint. This normal bifurcation of SN occurred in

sciatic nerve as it exits the greater sciatic notch in the

three female cadavers bilaterally (6 cases), in two

gluteal region

3,4,5

unilaterally (2cases) and in fifteen male cadavers

.

The high division of SN may give rise to

bilaterally (30 cases), and in three unilaterally (3

complications

cases).

during

intramuscular

injections,

anaesthesia or surgery in the gluteal region3,4,6 . The

In nine lower limbs (18% cases), the sciatic nerve

sciatic nerve may be damaged in misplaced

divided high above into tibial and common peroneal

therapeutic injections in the gluteal region and the

nerves, either in the sacral fossa or in the gluteal

nerve is vulnerable in posterior dislocation of hip

region. In two cadavers the sciatic nerve bifurcated in

2

joint .

the pelvis bilaterally and in the inferior extremities of

The present study was planned to describe the

the other five cadavers, high division of the nerve

variations in the division of the sciatic nerve at

was unilateral.

different levels with the clinical implications. 35 www.ijbamr.com P ISSN: 2250-284X , E ISSN : 2250-2858

Indian Journal of Basic and Applied Medical Research; June 2015: Vol.-4, Issue- 3, P. 34-44

Among these nine cases, in seven of them (14%), the

region unilaterally. In both the cases, the nerve

nerve bifurcated while in the pelvic cavity and tibial

passed through the piriformis muscle dividing it into

and common peroneal components emerged in the

superior and inferior slips to appear in the gluteal

gluteal region below the lower border of piriformis

region. Then after a short distance the sciatic nerve

separately. Four were right sided cases and three

divided in each case into tibial and common peroneal

were left sided. Among these seven cases, there was a

nerves. In the female cadaver, the left lower limb and

female cadaver with unilateral variation (1case) and

in the male cadaver, the right lower limb was

four male cadavers, where two of them had bilateral

concerned with this variation.

variation (4 cases) and two had unilateral variation (2

The photographs of eight cases with one normal

cases) of high division of SN in pelvis.

bifurcation of the SN are presented in this article, the

In the two other cadavers (4% cases), one male and

other case was similar to figure - 5.

one female, sciatic the nerve bifurcated in the gluteal Table – 1 Different levels of bifurcation of the sciatic nerve with percentage: Level of

Number of total

Bilateral

Unilateral

Bifurcation of SN

cases with

In 3 female cadavers –

In 2 female cadavers – 2 cases

sciatic nerve near

6 cases,

(one right and one left sided case).

the apex of the

In 15 male cadavers –

In 3 male cadavers –3 cases (two

popliteal fossa

30 cases.

left and one right sided case).

Total 36 (72% cases).

Total 5 (10% cases).

percentage

Division of the

41 (82%) cases.

In one female cadaver – 1 case Division of the

7 cases (14%)

sciatic nerve in the

In 2 male cadavers – 4 cases

(right sided).

(8%).

In 2 male cadavers – 2 cases (one right & one left).

pelvis

Total – 3 cases (6%).

Division of the

2 cases (4%)

Nil.

In one female cadaver – 1 case

sciatic nerve in

(left sided).

gluteal region

In 1 male cadaver – 1 case (right sided). Total – 2 cases (4%).

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Indian Journal of Basic and Applied Medical Research; June 2015: Vol.-4, Issue- 3, P. 34-44

Figures

Figure - 1; In a right sided lower limb of a female cadaver, the sciatic nerve (SN) passed between the two heads of the biceps femoris and divided into tibial and common peroneal nerves in the back of the knee joint. Index: A – Sciatic nerve, B - Tibial nerve, C - Common Peroneal nerve, D- Hamstring group of muscles, E – Lateral head of Gastrocnemius, F – Biceps Femoris muscle.

Figure – 3; In a left sided lower limb of a male cadaver, the sciatic nerve divided into tibial and common peroneal nerves in the pelvis and they emerged in the gluteal region below the piriformis muscle separately. Index : A – Piriformis muscle, B – Gluteus maximus muscle, C - Tibial nerve, D - Common Peroneal nerve, E – Tibial and Common Peroneal nerves running side by side from the gluteal region to the back of the thigh, F – Gluteus medius muscle.

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Indian Journal of Basic and Applied Medical Research; June 2015: Vol.-4, Issue- 3, P. 34-44

Figure – 4; The two components of SN (Tibial and Common Peroneal nerves) running side by side in the back of the left thigh of a male cadaver. Index : A- Tibial nerve, B- Common Peroneal nerve, C- Hamstring group of muscles.

Figure – 4 The two components of SN (Tibial and Common Peroneal nerves) running side by side in the back of the left thigh of a male cadaver. These two nerves seemed to have united as they ran very close to each other. Index : A- Tibial nerve, B- Common Peroneal nerve, C- Biceps femoris muscle, D – Semitendinosus muscle. 36 38 www.ijbamr.com P ISSN: 2250-284X , E ISSN : 2250-2858

Indian Journal of Basic and Applied Medical Research; June 2015: Vol.-4, Issue- 3, P. 34-44

Figure -5; In a right sided lower limb of a male cadaver, the tibial and common peroneal nerves emerged in the gluteal region below the piriformis muscle separately as the sciatic nerve bifurcated in the pelvis. Index : A – Tibial nerve, B – Common Peroneal nerve, C - Gluteus maximus muscle, D - Piriformis muscle, E – tricipital tendons of gemellus superior, obturator internus, gemellus inferior, G –Biceps femoris muscle, F – Semitendinosus muscle.

Figure - 6 ; In the right sided lower limb of a female cadaver, the sciatic nerve divided into tibial and common peroneal nerves in the pelvic cavity and emerged in the gluteal region below the piriformis separately to run in the back of the thigh passing deep to the origin of the long head of biceps femoris. Index : A – Tibial nerve, B – Common Peroneal nerve (both in the gluteal region and back of thigh), C - Piriformis muscle , D - Gluteus maximus muscle, E – Long head of Biceps Femoris muscle, F – Semimembranosus muscle.

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Indian Journal of Basic and Applied Medical Research; June 2015: Vol.-4, Issue- 3, P. 34-44

Figure– 7; Two divisions of the Sciatic Nerve (Tibial and Common Peroneal) emerged below the piriformis muscle in the gluteal region, passed to the back of the thigh deep to the origin of the Hamstring Muscles in the right lower limb of a male cadaver. Index : A – Tibial nerve, B – Common Peroneal nerve (both in the gluteal region and back of thigh), C - Piriformis muscle , D - Gluteus maximus muscle,

E – Inferior gluteal vessels and nerve, F- Long head of Biceps Femoris

muscle, G – Semitendinosus muscle, H- Semimembranosus muscle.

Figure - 8 ;In a leftt sided lower limb of a female cadaver, the Sciatic nerve emerged in the gluteal region through the divided piriformis and after a short distance divided into tibial and common peroneal nerves which ran in the back of the thigh. Index: A – Sciatic Nerve, B - Common Peroneal nerve, C - Tibial nerve, D – Long head of Biceps femoris, E – Semitendinosus, F – Semimembranosus.

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Indian Journal of Basic and Applied Medical Research; June 2015: Vol.-4, Issue- 3, P. 34-44

Figure – 9; The sciatic nerve emerged between the two slips of the piriformis muscle in the right sided gluteal region and then it was divided into tibial and common peroneal nerves in the same region in a male cadaver. Index: A- Sciatic Nerve,

B - Tibial nerve, C - Common peroneal nerve, D - piriformis muscle with upper and

lower slips, E – Gemellus superior, F - Gluteus medius muscle. Kirci et al in 1999, described a case with unilateral Discussion

double piriformis and high division of sciatic nerve

A number of variations in the course and distribution

where the common peroneal nerve passed between

of the sciatic nerve (SN) has been reported.

the two parts of piriformis and the tibial nerve

Bifurcation into its two major divisions (common

emerged under the lower border of inferior piriformis

peroneal and tibial) may occur anywhere between the

9

sacral plexus and the lower part of the thigh. The two

In a case presented by Paval et al in 2008, bifurcation

terminal branches of the sciatic may arise directly

of the sciatic nerve in pelvis was found bilaterally in

from the sacral plexus7.

a 70 year old male cadaver. Common peroneal nerve

In 85-89% cases, the nerve divides into the terminal 1

.

pierced the piriformis dividing the muscle into upper

branches at the apex of the popliteal fossa ; in the

and lower slips whereas the tibial nerve emerged

present study this percentage is 82%.

below the lower slip of the piriformis on both sides 4.

Smoll compiled the results of 18 previous studies

Khan et al (2011) found a case where on the left side

and 6,062 cadavers to find that the prevalence of high

common peroneal nerve passed between the two

division of sciatic nerve in cadavers was 16.9% and

divisions of piriformis and tibial nerve passed below

8

in surgical case series was 16.2% . In the present

the inferior piriformis5. In all these three cases, the

study, the prevalence of this variation (high division

sciatic nerve divided inside the pelvis before

of SN) was 18%. According to Smoll again, the

emerging in the gluteal region.

piriformis and SN variations have ranged from 1.5 – 8

In 2013, Bhattacharya et al presented a case with

3.58% in dissected human cadavers and in our study

double piriformis and division of the sciatic nerve in

this variation is present in 4% cases.

pelvis; the common peroneal nerve emerged between

the two piriformis muscles, whereas the tibial nerve 39 41 www.ijbamr.com P ISSN: 2250-284X , E ISSN : 2250-2858

Indian Journal of Basic and Applied Medical Research; June 2015: Vol.-4, Issue- 3, P. 34-44

emerged below the lower piriformis on a left inferior

also be caused by directly due to a lumbar disc

extremity. On the right side sciatic nerve divided in

pressing on the sciatic nerve as it exits the

the gluteal region after emerging from the lower

intervertebral foramen in the lumbar spine3,13,14 .

border of piriformis 10.

Investigations like CT scan, MRI, EMG, nerve

In 2014, Saritha et al described few variations of

conduction test are routinely done to detect nerve

Sciatic nerve bifurcation in 4 cadavers from their

pathology1.

study and their findings have similarities with those

In piriformis syndrome, the sciatic nerve can be

revealed in the present study like SN dividing in the

entrapped between the gemellus superior and

1

4,15

pelvis .In 2014, Patil et al described an unique case

piriformis muscles

. Another common site of

where dorsal and ventral divisions of ventral rami of

entrapment is when the sciatic nerve or one of its

lower lumbar and sacral spinal nerves passed ventral

branches pierces the piriformis muscle and this can

and dorsal to the piriformis muscle respectively.

occur in about 1% to 5% of all humans4,13,16. In that

These divisions joined each other below the

case myospasm and or contraction of the piriformis

piriformis muscle to form sciatic nerve. This low

muscle itself can lead to pain along the buttock, back

formation of sciatic nerve was observed in distal part

of the thigh to the knee, loss of sensation or

of left gluteal region of a 50-year-old male cadaver.

numbness and tingling into the leg and sole of the

The sciatic nerve then passed caudally into back of

foot3,11. Piriformis syndrome is often misdiagnosed as

thigh and divided into tibial and common peroneal

sciatica due to similar symptoms 4, 13,14,17 .

nerves in the upper part of popliteal fossa. Such

Some workers consider piriformis syndrome to be

variations may lead to piriformis syndrome or non-

a form of myofascial pain syndrome 3,4,5. A history of

discogenic sciatica11.

trauma may be present in approximately 50% of

Most of the text books of Anatomy, Surgery and

cases of the syndrome. The trauma is not usually

Orthopaedics state that the sciatic nerve bifurcation

sudden in onset and may occur several months before

1

levels are important in clinical and treatment aspects .

the initial symptoms treated in the orthopaedics or

This high division of sciatic nerve can cause nerve

physical

Medicine 1,18

department

along

with

entrapment under other anatomic structures, resulting

rehabilitation

in non-discogenic sciatica, piriformis syndrome or

among the athletes as a part of sport injury 19. It may

coccydynia and muscle atrophy

1,5

. This variation of

also

follow

. This syndrome can also be present

total

hip

replacement

surgery3,4.

sciatic nerve may result in nerve injury during deep

Complete medical history and physical examination

intramuscular injections in the gluteal region,

are necessary for differential diagnosis of this

sciatica, piriformis syndrome, failed SN block in

syndrome 4,18.

anesthesia

or incomplete block of SN during

The management of piriformis syndrome includes

anesthesia, injury during posterior

analgesic, muscle relaxants, injection of local

hip operations and other surgery in the gluteal region

anesthetic agents, steroid (like methylprednisolone)

1,4, 6,9,12

or botulinum toxin into the piriformis muscle; liquid

popliteal block

.

Low back pain, caused by a compression or irritation 1

of the sciatic nerve is called sciatica . Sciatica may

anaesthetic agents can be injected to the area of sciatic nerve even3,4,5, 10,15,18 . To avoid blind injection 42 35

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Indian Journal of Basic and Applied Medical Research; June 2015: Vol.-4, Issue- 3, P. 34-44

in

the gluteal region,

Anatomical landmarks,

the surrounding muscles like obturator internus,

electromyography or computed tomography (CT),

gemelli, or quadratus femoris, as these muscles have

fluoroscopic guidance will be helpful to identify the

common insertions like piriformis muscle4,5,10.

piriformis muscle and a nerve stimulator can be used

The knowledge and Information about different

for sciatic nerve identification

4,5, 10,12,13

. Surgery

variations of sciatic nerve bifurcation, will not only

may be considered when the piriformis is involved in

make the surgeons careful, but will also help them

the sciatic nerve entrapment. The muscle may be

regarding proper planning for surgical intervention in

thinned, divided or excised to be compensated with

the gluteal region or in the thigh 6 .

Table – 2 Findings of the present study and the previous studies Variations of SN

Findings of the present study

Findings of the previous studies

Sciatic nerve (SN) bifurcated at

82% cases

85-89% cases1

18% cases

16.9% cases in cadavers8

the apex of the popliteal fossa

Sciatic nerve bifurcated high

16.2% surgical cases8

above

Piriformis and SN variations

4% cases

1.5 – 3.58% cases8

Conclusion

especially among the athletes. This study will also

The variations of the bifurcation of sciatic nerve have

enhance our knowledge in Gross Anatomy and

clinical implications regarding deep intramuscular

Clinical Anatomy.

injections, popliteal block anaesthesia, hip surgery,

Acknowledgement

practice of neurology etc. Moreover, this study will

We are grateful to Professor Hasi Dasgupta, Dr.

have a contribution in Sports Medicine and

Manotosh Banerjee and other members of the

rehabilitation as the high level of division of the

Department of Anatomy, Nilratan

sciatic nerve and variation in the piriformis muscle

College, Kolkata, India, for their kind co-operation to

may be the causes of soft tissue problems of hip,

complete this study.

Sircar Medical

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