Sciatic Nerve Anatomy

The sciatic nerves branches from your lower back through your hips and buttocks and down each leg. Sciatica refers to pain that travels along the path of the sciatic nerve
Nerve roots: L4-S3.
Motor functions:
Innervates the muscles of the posterior thigh (biceps femoris, semimembranosus and semitendinosus) and the hamstring portion of the adductor magnus (remaining portion of which is supplied by the obturator nerve).
Indirectly innervates (via its terminal branches) all the muscles of the leg and foot.
Sensory functions: No direct sensory functions. Indirectly innervates (via its terminal branches) the skin of the lateral leg, heel, and both the dorsal and plantar surfaces of the foot.

1. Anatomy of Sciatic Nerve Dr Mathew Joseph MBBS, MD(AIIMS), BCC(Palliative Medicine) Assistant Professor Department of Anatomy Amala Institute of Medical Sciences, Thrissur

2. Learning Objectives: By the end of the lecture, the students should be able to: Describe the anatomy (origin, course & distribution) of the sciatic nerve. List the branches of the sciatic nerve. Describe briefly the main motor and sensory manifestations in case of injury of the sciatic nerve or its main branches.

3. Self Assesment A patient presented with severe chronic lower back pain in the sacral region with radiation to the back of the left leg, producing a strong pain throbbing and burning behind the knee. Pain was aggravated when bending forward or in reaching out position. He gave history of an accident that resulted in fracture of the lumbar vertebrae. His MRI two months prior to this severely increasing pain , revealed disc degeneration, and protrusion of the disc at the S1 level. Which anatomical structure is likely to be involved ?

4. Lumbo-Sacral Plexus P ovides the nerve supply to the pelvis and lower limb - in addition to part of the autonomic supply to the pelvic viscera. S ciatic nerve I nferior gluteal nerve S uperior gluteal nerve P udendal n erve Nerve to quadratus femoris Nerve to obturator internus P osterior cutaneous n erve of the thigh .

5. Let’s Draw Lumbo-Sacral Plexus....

6. The sciatic nerve A major nerve of the lower limb. It is a thick flat band, approximately 2cm wide The L argest and Thickest nerve in the body. It is composed of 2 parts : Components: Tibial and C ommon peroneal Ventral divisions of Anterior primary rami of L4, L5 , S1, S2, S3 - T ibial part. Dorsal divisions of A nterior primary rami of L4, L5 , S1, S2 - C ommon peroneal part.

7. The S ci a tic nerve

8. The Sciatic Nerve : Extent It commences in the pelvis. It ends at or just above the superior angle of the popliteal fossa by dividing into: Tibial nerve Common Peroneal nerve

9. The Sciatic Nerve : Course In the pelvis, it is located in front of piriformis under cover of its fascia . It enters the gluteal region via greater sciatic foramen below the piriformis. In gluteal region It lies under cover of gluteus maximus. Here it runs downward with small lateral convexity and enters between the ischial tuberosity and greater trochanter .

10. No t e **** T he sciatic nerve can be described as two individual nerves bundled together in the same connective tissue sheath – the tibial and common peroneal nerves. These usually separate at the apex of the popliteal fossa, however in approximately 12% of people they separate as they leave the pelvis.

11. Variations in the manner of departure of the sciatic nerve from pelvis Normally the sciatic nerve enters the gluteal region via greater sciatic foramen below the piriformis. Occasionally sciatic nerve splits into tibial and common peroneal elements inside the pelvis. In such cases, the manner of exit from pelvis happens as follows: The c ommon peroneal nerve goes through the piriformis and tibial nerve enters below the piriformis (12%). The common peroneal nerve enters above the piriformis and tibial nerve enters below the piriformis (0.5%).

12. Sci a tic ne r v e

13. S ciatic Nerve: Surface Marking The sciatic nerve is marked on the back of thigh by joining the following 3 points: The first point is marked 2.5 cm lateral to the midpoint of the line joining the pos terior superior iliac spine and ischial tuberosity. 2nd point is marked halfway between the ischial tuberosity and greater trochanter. The third point is indicated in the junction of the upper 2/3rd and lower 1/3rd of the back of the thigh.

14. A thick curved line (about 2 cm wide) with outward convexity joining the first and 2nd points represents the sciatic nerve in the gluteal region and a thick straight line of exactly the same width joining the 2nd and third points represents the sciatic nerve in the thigh.

15. The Sciatic Nerve: Relations D eep Relations ( B ed of Sciatic nerve ) From above downward the sciatic nerve is related to: Body of ischium (posterior surface) Tendon of obturator internus Gemellus superior Gemellus inferior Quadratus femoris Adductor magnus

16. The Sciatic Nerve: Relations Superficial relations From above downward, the sciatic nerve is related to: Gluteus maximus (in the gluteal region). Long head of biceps femoris (in the thigh). The sciatic nerve is reachable on the back of the thigh, only in the angle between the gluteus maximus and long head of biceps femoris.

17. The Sciatic Nerve: Branches Articular branches to the hip joint originate in the gluteal region. Muscular branches to the hamstring muscles originate in the lower part of the gluteal region or in the upper part of the thigh from the medial side of the nerve. Muscular branch to the short head of biceps femoris originates in the lower part of the thigh from the lateral side of the nerve.

18. Note*** All the muscular branches of the sciatic nerve originate from the medial side with the exception of nerve to short head of biceps femoris, which originates from the lateral side. Thus, the side lateral to the sciatic nerve is safe side and the side medial to its dangerous side/unsafe side.

19. Summary

20. The Sciatic Nerve: Motor Functions Although the sciatic nerve passes through the gluteal region, it does not innervate any muscles there. However, the sciatic nerve does directly innervate the muscles in the posterior compartment of the thigh , and the hamstring portion of the adductor magnus. The sciatic nerve also indirectly innervates several other muscles, via its two terminal branches: Tibial nerve – the muscles of the posterior leg (calf muscles), and some of the intrinsic muscles of the foot. Common fibular nerve – the muscles of the anterior leg, lateral leg, and the remaining intrinsic foot muscles. In total, the sciatic nerve innervates the muscles of the posterior thigh, entire leg and entire foot.

21. The Sciatic Nerve: Sensory Functions The sciatic nerve does not have any direct cutaneous functions. It does provide indirect sensory innervation via its terminal branches: Tibial nerve – Innervates the posterolateral and anterolateral sides of the leg, and the plantar surface of the foot (the sole). Common peroneal nerve – Innervates the lateral leg and the dorsal surface of the foot.

22. The Sciatic Nerve: Clinical Relevance Intramuscular Injections The anatomical course of the sciatic nerve must be considered when administering intramuscular injections into the gluteal region. The region can be divided into quadrants using 2 lines, marked by bony landmarks: One line descends vertically from the highest point on the iliac crest. The other horizontal line passes through the vertical line half way between the highest point on the iliac crest and ischial tuberosity. The sciatic nerve passes through the lower medial quadrant. To avoid damaging the sciatic nerve therefore, intramuscular injections are given only in the upper lateral quadrant of the gluteal region.

23. The Sciatic Nerve : Injury P enetrating wounds P osterior dislocation of the hip F racture of the pelvis Iatrogenic Motor Deficits Inability to stretch the thigh and bend the knee, as a result of paralysis of the hamstring muscles. Loss of all movements below the knee with foot drop, because of paralysis of all the muscles of the leg and foot. The motor loss results in flail foot ( Foot Drop ) that results in great trouble in walking. The patient walks with high-stepping gait . Sensory loss The sensory loss on the back of the thigh and entire of the leg and foot with the exception of the area innervated by the saphenous nerve , because of participation of the cutaneous nerves originated from the tibial and common peroneal nerves.

24. The Sciatic Nerve : Neuropathy As the sciatic nerve moves outof the pelvis, occasionally, it goes through the piriformis muscle . I t might become entrapped leading to piriformis syndrome. It’s a common anatomical form but an incredibly uncommon entrapment neuropathy.

25. The Sciatic Nerve: Sciatica It is a term applied to a clinical condition defined by shooting pain felt along the course of distribution of the sciatic nerve (example, buttock, posterior aspect of the thigh, lateral aspect of the leg, and dorsum of the foot. It happens because of compression and aggravation of L4 S3 spinal nerve roots by herniated intervertebral disc of the lumbar vertebrae .

26. The Sciatic Nerve : Sleeping Foot The sciatic nerve is uncovered on the back of thigh in the angle between the lower border of gluteus maximus and long head of biceps femoris. The temporary compression of the sciatic nerve against femur at the lower border of gluteus maximus causes paresthesia in the lower limb . It is named “sleeping foot, example, when a man sits on the hard edge of the seat for a long time” .

27. Self Assesment A patient presented with severe chronic lower back pain in the sacral region with radiation to the back of the left leg, producing a strong pain throbbing and burning behind the knee. Pain was aggravated when bending forward or in reaching out position. He gave history of an accident that resulted in fracture of the lumbar vertebrae. His MRI two months prior to this severely increasing pain , revealed disc degeneration, and protrusion of the disc at the S1 level. Which anatomical structure is likely to be involved ?

28. Thank You