Lumbosacral Plexus

Front 1

what does the LUMBOSACRAL plexus innervate

Back 1

- entire lower limb, except some skin of BUTTOCK
(supplied by segmental nerves: post rami of upper lumbar & upper sacral)

Front 2

Lumbar plexus
- location
- supplies what [3]
- braches (location, supplies what) [6]

Back 2

L1-L4, plexus within psoas major
- supplies anterior thigh
- supply psoas major ms
- supply lower abd wall

1. Iliohypogastric (L1)
- lateral branch → upper lateral quadrant of buttock

2. Ilioinguinal (L1)
- skin below medial part of inguinal ligament

3. Genitofemoral (L1, L2)
- genital branch → motion (e.g. cremaster)
- femoral branch → sense (skin over femoral triangle)

4. Lateral cutaneous n of thigh (L2, L3)
- skin over lateral thigh

5. Femoral (L2, 3, 4)

6. Obturator (L2, 3, 4)

Front 3

which lumbar nerves:
- supply lower abd wall?
- supply inguinal canal, ext genitalia, ant. scrotum?

Back 3

- iliohypogastric, ilioinguinal
- ilioinguinal, genitofemoral

Front 4

what are the cutaneous nerves of the lumbar plexus? [4]

Back 4

- lateral branch of iliohypogastric
- ilioinguinal
- femoral branch of genitofemoral
- lateral cutaneous

Front 5

Sacral plexus
- location
- innervation [4]
- main branches [8]

Back 5

- L4-5, S1-S4, on surface of piriformis ms in pelvis.

- musculature of buttock
- posterior thigh
- entire leg & foot below knee (except area of skin supplied by saphenous nerve)
- perineum & pelvic diaphragm (pudendal n)

1. Sciatic (common fibular + tibial) [L4-S3]
- gluteal muscle

2. Superior & inferior gluteal [L4-S1, L5-S2]
- leg & foot

3. N to piriformis [S1-2]

4. N to quadratus femoris [L5-S1]
+ inferior gemellus

5. N to obturator internus [L5-S1]
+ superior gemellus

6. Post. cutaneous nerve of thigh [S1-S3]

7. Pudendal [S2-S4]
- perineum

8. N. to levator ani [S4-S5]
- levator ani, coccygeus

Front 6

Which nerves
- are lateral rotator of hip joint?
- supply buttock?

Back 6

Lat rotator
- superior & inferior gluteal nerves
- nerve to piriformis
- nerve to obturator internus
- nerve to quadratus femoris

Supply buttock:
- nerve to piriformis
- nerve to obturator internus
- nerve to quadratus femoris

Front 7

Describe the path of the:
- sciatic nerve
- obturator nerve
- femoral nerve

Back 7

- Sciatic → greater sciatic foramen
- obturator → obturator foramen
- femoral n. → in front of hip bone

Front 8

Femoral nerve
- location
- course
- muscle supplied, skin supplied [3]
- injury [3]

Back 8

- posterior divisions, L2-L4
- breaks into branches as it enters thigh, ant to hip bone, under inguinal ligament

- Ms branch → ms of ant. (extensor) thigh muscles
- medial & intermediate cutaneous n. → medial thigh
- Saphenous nerve (longest br) → skin on medial leg/foot

Injury:
- Paralyzed quadriceps femoris → unstable knee (buckles when walking)
- Ant. trunk bending (press thigh ms when walking)
- Sensory loss

Front 9

Obturator nerve
- location
- course [2]
- muscle & skin supplied [2]
- injury

Back 9

= anterior divisions, L2-4

- lies deep between psoas major & pelvic brim
- enter thigh through obturator foramen

- Medial (adductor) thigh ms & obturator externus
- skin: small area of medial thigh

Injury:
- leg swings out during walking

Front 10

Sciatic nerve
- location
- course [3]
- muscle and skin supplied [3]
- injury [2]

Back 10

- L4-S3

- leaves pelvis through greater sciatic notch (1/3 down line joining PSIS & ichial tuberosity).
- Leaves buttock midway between ischial tuberosity + greater trochanter
- branch 2/3 way down thigh → tibial, common peroneal nerves

Supply:
- posterior thigh ms, all ms in leg & foot
- skin of whole leg & foot except medial side
- tibial component → hamstrings except short head of biceps femoris [common peroneal]

Injury:
- ms paralysis in leg/foot + loss of sensation except medial side
- if lesion above origin of branches, limb can't bear weight for walking

Front 11

relationship of the sciatic nerve to piriformis

Back 11

87.5% people: nerve comes out BELOW piriformis
12% pierces piriformis
0.5% above piriformis

(so any post. dislocation of hip joint → impinge on sciatic nerve as it is usually behind hip joint)

Front 12

Tibial nerve
- location
- course
- supplies [4]
- injury

Back 12

- anterior division, L4-5, S1-3

- pass through popliteal fossa → below soleus muscle
- divide → medial & lat plantar nerve in sole of feet

Supply:
- post flexor thigh & leg (plantar flexor) ms.
- med/lat plantar n. → plantar feet muscle
- skin on posterolateral leg
- sural nerve → skin of foot (sole)

Injury:
- rigid inelastic foot (cannot plantarflex) → limp
- paralysis of gastrocnemius & soleus

Front 13

Common/peroneal nerve
- location
- path [3]
- supply [2]
- injury

Back 13

- post division, L4-S2

- margin of biceps femoris
- winds around neck of fibula (vulnerable spot)
- divide → superficial & deep peroneal n.

Supply
- superficial PN → lateral (everter) leg muscle, skin of lateral leg, dorsum of foot
- deep PN → ant. (dorsiflexor) leg ms, extensors of toes

Injury
- foot drop + steppage gait
- can't dorsiflex foot (foot drags when walking)

Front 14

Superior gluteal nerve
- location
- path
- supply [1]
- injury [2]

Back 14

- post division, L4-5, S1

- leave pelvis via greater sciatic foramen, above piriformis

- abductors of hip joint (gluteus medius, gluteus minimus, tensor fasciae latae)

Rmb small gluteus ms stabilizes pelvis in coronal plane
- One side → dipping gait, Trendelenburg sign
- both sides → waddling gait

Front 15

Inferior gluteal nerve
- location
- path
- supply
- injury

Back 15

- post division L5, S1-2

- leave pelvis via greater sciatic foramen, BELOW piriformis

- gluteus maximus, chief extensor of thigh

Injury
- difficult to stand up from seated position
- can't bend down w/o overbalancing
- post trunk bending: extensor lurch gait

Front 16

features of the dermatome

Back 16

- more distorted than upper limb because of medial rotation & extension from fetal position of flexion
- stand on S1
- lie on S2
- sit on S3
- wipe on S4

Front 17

What is sciatica?

Back 17

- set of symptoms w. pain & numbness → compression/irritation to:
- L4, L5, S1
- L4-S3 → sciatic nerve

Front 18

general rule for myotome

Back 18

- occupy 4 continuous segments
- upper 2 segment → innervate 1 movement
- lower 2 segment → innervate opposite movement
[start from L2, move down spinal centre for 1 joint]

Front 19

Spinal centres for joint movement

Back 19

Hip
- L2-3: flexion, adduction, medial rotation
- L4-5: extension, abduction, lateral rotation

Knee:
- L3-4: extension [Knee jerk ~ patella ligament]
- L5-S1: flexion

Ankle:
- L4-5: dorseflexion
- S1-2: plantarflexion (Ankle jerk~Achilles tendon)

Foot:
- L4: inversion
- L5-S1: eversion (plantar reflex)