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Sciatic nerve

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Sciatic nerve

  1. 1. Sciatic Nerve Dr M Idris Siddiqui
  2. 2. LUMBOSACRAL PLEXUS • The lumbosacral plexus provides the nerve supply to the pelvis and lower limb, in addition to part of the autonomic supply to the pelvic viscera. • It gives origin to the sciatic, inferior gluteal, superior gluteal and pudendal nerves. • In addition, the nerves to quadratus femoris, obturator internus and the posterior cutaneous nerve of the thigh also arise from LUMBOSACRAL PLEXUS .
  3. 3. The sciatic nerve • The sciatic nerve is a major nerve of the lower limb. • It is a thick flat band, approximately 2cm wide –The largest nerve in the body. • It is composed of 2 parts: –Tibial and common peroneal nerves. • Ventral divisions of anterior primary rami of L4, L5; S1, S2, S3 compose the tibial part. • Dorsal divisions of anterior primary rami of L4, L5; S1, S2 compose the common peroneal part.
  4. 4. The sciatic nerve
  5. 5. 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.
  6. 6. Origin • The sciatic nerve originates from lumbosacral plexus L4-S3 –Tibial division • Orginates from anterior preaxial branches of L4,L5,S1,S2,S3 –Peroneal division • Originates from from postaxial branches of L4,L5,S1,S2
  7. 7. 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.
  8. 8. Note • the 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. •
  9. 9. 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 common 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%).
  10. 10. Sciatic nerve
  11. 11. SURFACE MARKINGS • 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 anterior 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.
  12. 12. 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.
  13. 13. RELATIONS • DEEP RELATIONS (BED OF THE SCIATIC NERVE) • From above downward the sciatic nerve is related to: –Body of ischium (posterior surface). –Tendon of obturator internus –Gemellus superior –Gemellus inferior muscles. –Quadratus femoris. –Adductor magnus.
  14. 14. 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.
  15. 15. 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.
  16. 16. BRANCHES • 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.
  17. 17. Summary
  18. 18. 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.
  19. 19. 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.
  20. 20. 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.
  21. 21. INJURY OF THE SCIATIC NERVE • The sciatic nerve could possibly be injured by penetrating wounds, posterior dislocation of the hip, fracture of the pelvis, surgery . Listed here are the characteristic clinical features: • 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 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.
  22. 22. Sciatic Nerve Neuropathy • As the sciatic nerve makes the pelvis, occasionally, it goes through the piriformis muscle and at that stage, it might become entrapped leading to piriformis syndrome. It’s a common anatomical form but an incredibly uncommon entrapment neuropathy.
  23. 23. 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.
  24. 24. 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”.

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