Lumbosacral plexus

Question 1

What forms the lumbar plexus?

Answer 1

Anterior rami of L1-L4 spinal nerves

Question 2

What forms the lumbosacral trunk?

Answer 2

anterior rami of L4 and L5

Question 3

What are the 5 major peripheral nerves of the lumbar plexus and what are their root values (6 in reality but 5 for MSK)?
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Answer 3

Ilioinguinal (L1)
Genitofemoral (L1, L2)
Lateral cutaneous (L2, L3)
Obturator (L2, L3, L4)
Femoral (L2, L3, L4)

Question 4

What does the ilioinguinal nerve innervate?

Answer 4

Skin of genitalia and upper medial thigh

Question 5

What does the genitofemoral nerve innervate?

Answer 5

Femoral branch = skin on the upper anterior thigh 
Genital branch (reproductive unit)

Question 6

What does the lateral (femoral) cutaneous nerve of the thigh innervate?

Answer 6

Cutaneous sensation to anterolateral thigh to the knee

Question 7

What does the obturator nerve innervate?

Answer 7

Skin over medial thigh and muscle of the median compartment

Question 8

What does the femoral nerve innervate?

Answer 8

Skin of anterior thigh (anterior femoral cutaneous branch)
Skin of medial leg (saphenous branch)
Muscles of anterior compartment of thigh

Question 9

What forms the sacral plexus?

Answer 9

Anterior rami of S1-S5

-also has lumbosacral trunk (L4+L5) contribution

Question 10

What are the 5 branches of the sacral plexus and what are their nerve roots?
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Answer 10

Superior gluteal (L4, L5, S1)
Inferior gluteal (L5, S1, S2)
Sciatic (L4, L5, S1, S2, S3)
Posterior femoral (S1, S2, S3)
Pudendal (S2, S3, S4) - reproductive unit

Question 11

Describe briefly how each branch of sacral plexus leave the pelvis

Answer 11

Superior gluteal = greater sciatic foramen and enter gluteal region above piriformis

Inferior gluteal = greater sciatic foramen and enter gluteal region below piriformis

Sciatic = greater sciatic foramen and enter gluteal region below piriformis

Posterior femoral = greater sciatic foramen and enter gluteal region below piriformis

Pudendal = greater sciatic foramen then enters lesser sciatic foramen by looping across supraspinous ligament

Question 12

What are the structures that leave the greater sciatic foramen BELOW piriformis?

Answer 12

• Inferior gluteal nerve, artery and vein
• Sciatic nerve
• Posterior femoral cutaneous nerve
• Nerve to quadratus femoris
• Nerve to obturator internus
• Pudendal

Question 13

What are the two branches of the sciatic nerve?

Answer 13

Tibial nerve and Common peroneal (common fibular) nerve

Question 14

What are the root values of the tibial nerve of the (sciatic foramen) and what does it innervate?

Answer 14

Ventral divisions of L4-S3

-hamstring muscles (semimembranosus, semitendinosus, biceps femoris (long head)) and hamstring part of adductor magnus

Question 15

What are the root values of the common peroneal (common fibular) nerve of the (sciatic foramen) and what does it innervate?

Answer 15

Dorsal divisions of L4-S2

-Short head of biceps femoris

Question 16

Why should you be careful when giving injections in the gluteal region?

Answer 16

Can cause sciatic nerve damage

Question 17

What are the two regions where you can administer injections in the gluteal region?

Answer 17

1) Dorsogluteal site (3-7 y/o) = uppper outer quadrant
2) Ventrogluteal site (7+ y/o) = in between index and middle finger (placing palm on greater trochanter and index pointing towards anterior superior iliac crest)