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MBBS II MSS > L17 - LUMBOSACRAL PLEXUS & NERVE DISTRIBUTIONS > Flashcards

L17 - LUMBOSACRAL PLEXUS & NERVE DISTRIBUTIONS Flashcards

1
Q

What does the Lumbar plexus innervate and omit?

A

lower limb is entirely innervated by branches of the lumbosacral plexus.

Exception: some skin of the buttock, which is supplied by segmental nerves (posterior rami of upper lumbars and upper sacrals)

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2
Q

Define the parts of lumbosacral plexus?

A

Lumbar plexus = Ant rami L1-L4

Sacral plexus = Ant rami L4-L5, S1-S4

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3
Q

List the 6 main branches of the Lumbar plexus?

A

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1) Iliohypogastric nerve
2) Ilioinguinal nerve
3) Genitofemoral nerve
4) Lateral cutaneous nerve of thigh
5) Obturator nerve
6) Femoral nerve

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4
Q

What is the course of Genitofemoral nerve?

A

L1-L2

Penetrate Psoas major > branch to femoral and genital branches

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5
Q

Which nerves from lumbar plexus go emerge from the superficial inguinal ring?

A

Ilioinguinal n.

Genital branch of genitofemoral n.

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6
Q

What are the cutaneous nerves of the lumbar plexus? Which areas of skin supplied

A

1) Lateral cutaneous nerve of thigh for skin&raquo_space; lateral thigh
2) Femoral branch of Genitofemoral nerve&raquo_space; middle inguinal ligament, skin over femorla triangle
3) Ilioinguinal nerve&raquo_space; medial thigh + external genitalia
4) Lateral branch of Iliohypogastric nerve&raquo_space; upper lateral quadrant of gluteal muscle

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7
Q

What does the sacral plexus supply and what does it omit?

A

Supply: buttock muscles, Posterior thigh, entire leg and foot below knee, perineum, pelvic diaphragm

Except: area of skin supplied by saphenous nerve

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8
Q

Location of sacral plexus?

A

Lies on surface of piriformis muscle in the pelvis

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9
Q

List the 6 branches of the sacral plexus?

S,S,Np,No,Nq,P

A

(a) Sciatic nerve
(b) Superior & inferior gluteal nerves
(c) Nerve to piriformis
(d) Nerve to quadratus femoris (also supplies inferior gemellus)
(e) Nerve to obturator internus (also supplies superior gemellus)
(f) Posterior femoral cutaneous nerve
(g) Pudendal nerve

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10
Q

Which nerve branches from the sacral plexus supply the buttock?

A

Superior and inferior gluteal nerves

N. to prirformis

N. to obturator internus

N. to quadratus femoris

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11
Q

What are the 3 exits for nerves around the pelvis?

A

1) Greater sciatic foramen (below piriformis muscle: sciatic nerve, superior and inferior gluteal nerve)
2) Obturator foramen, covered by obturator membrane with small hole for obturator nerve
3) Anterior to hip bone (femoral nerve)

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12
Q

Root and supply of Femoral Nerve?

A

Root = Posterior division of L2,3,4, Lumbar plexus

Muscles supplied by branches: Extensors:
- Iliacus, Pectineus, Sartorius, Quadriceps femoris

Skin supplied by branches:

  • Intermediate and medial cutaneous nerves of thigh
  • Saphenous nerve (medial leg down to MCP of big toe)
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13
Q

Course of femoral nerve?

A

Lie lateral to Psoas muscle, pass at mid-point of inguinal ligament (femoral triangle VAN medial to lateral)

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14
Q

Result of injury to Femoral nerve?

A

Paralysis of Quadriceps femoris:

Knee joint unstable, cannot extend in stance phase

Hand used to force extension

Difficulty walking or standing, sensory loss

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15
Q

Root and supply of Obturator Nerve?

A

Root = Anterior division L2,3,4, Lumbar plexus

Supply Adductors of thigh:

  • Obturator externus
  • Adductor brevis
  • Adductor longus
  • Gracilis
  • Adductor magnus (adductor part)

Supply small area of skin at medial thigh

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16
Q

Course of Obturator nerve?

A

Lies deeply, between psoas major and pelvic brim.

Enters thigh through obturator foramen.

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17
Q

Where does the obturator nerve branch? Supply of the sub-branches?

A

Branch as it corsses Adductor brevis:

Anterior branch supplies Gracilis, Adductor longus

Posterior branch supplies Adductor magnus, Obturator externus, Adductor brevis

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18
Q

Results of injury to obturator nerve?

A

limb tends to swing out during walking

i.e. during surgery on ovaries

(Obturator nerve lies very deep and unlikely to damage)

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19
Q

Define the course of the sciatic nerve through the buttock.

A

PSIS, Ischial tuberosity and greater trochanter forms 3 corners of the triangle

Enters triangle at upper 1/3 between PSIS and Ischial tuberosity

Exits triangle halfway between Ischial tuberosity and Greater trochanter

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20
Q

Where to inject intramuscular at buttock?

A

Must miss the triangle formed by PSIS, Ischial tuberosity and Greater trochanter

Inject at Gluteus medius at upper right quadrant of buttock

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21
Q

What is the relationship of the sciatic nerve to piriformis?

A
  1. 5% population = sciatic nerve passes below piriformis
  2. 5% = pass above

12% = sciatic nerve’s commone peroneal component pierce through piriformis*

*Compressed by prirformis contraction

22
Q

Division and Supply of sciatic nerve?

A

All Hamstrings; all muscles in leg and foot:

2 components:**
- Tibial component = ventral division of L4-S3 = Hamstrings

  • Common peroneal/Fibular component = dorsal division of L4-S2 =Short head of biceps femoris
23
Q

Result of Sciatic nerve injury?

A
  • Paralysis of all muscles in leg and foot + sensory loss (except the medial side)
  • If lesion is above the origin of the tibial and common peroneal component, the limb cannot bear weight anymore
24
Q

What can cause lesion of the sciatic nerve?

A

Posterior dislocation of hip causes femoral head to crush the nerve

25
Q

Root and muscle supply of Tibial nerve?

A

Root = branch from sciatic nerve , Anterior divisions L4,5, S1,2,3)

Supply = Hamstrings (except short head of biceps femoris) + posterior muscles of the leg + plantar muscles.

26
Q

What skin does the tibial nerve innervate?

A

Posterolateral side of leg and lateral border of foot (sural nerve);

sole of foot (Medial and Plantar nerves)

27
Q

Branches of Tibial nerve?

A

Goes behind medial malleolus to plantar aspect

> > divides in the sole to medial and lateral nerves to innervate skin of foot sole

28
Q

What are the homologous structures in the upper limb like tibial nerve in the leg?

A

Lateral: median nerve, radial nerve

Medial: ulnar nerve

29
Q

Result of tibial nerve damage?

A

Paralyzed soleus and gastrocnemius

Cannot heel off and toe off normally with locked ankle

> > Rigid, inelastic foot with loss of sensation on sole

30
Q

Root and branches of Common peroneal nerve?

A

Root = branch of Sciatic nerve, posterior division L4,5, S1,2,3)

Runs along margin of biceps femoris&raquo_space; winds around neck of fibula

> > divides into superficial and deep peroneal nerves.

31
Q

What do the branches of Common peroneal nerve innervate?

A

Superficial peroneal nerve = Everters, skin over lateral leg and dorsum of foot

Deep peroneal nerves = Dorsiflexors of ankle, extensors of toes + small area of skin between toe 1 and 2

32
Q

High-stepping gait/ Foot drop is a symptom of what nerve damage?

A

Drag toes or exaggerated high stepping because of failure to Dorsiflex foot:

Must be deep peroneal nerve damage

33
Q

Where is the common peroneal nerve likely to be damaged? Example of injury?

A

Around neck of fibula

Fibula fracture can crush common peroneal nerve

34
Q

Describe the organization of the muscle groups and nerve supply of the thigh.

A

4 compartments

Anterior = Extensors > Femoral nerve

Lateral = Abductors > Superior gluteal nerve

Inferior = Flexors > Sciatic nerve

Inferomedial = Adductor magnus*** > Sciatic nerve and obturator nerve

Medial = Adductors > Obturator nerve

Anteromedial = Pectineus*** > Obturator and femoral nerves

*** Pectinues and Adductor magnus have MERGED MYOTOMES with dual innervation

35
Q

Which muscles in the thigh have merged myotomes?

A

*** Pectinues and Adductor magnus have MERGED MYOTOMES with dual innervation

36
Q

Root and supply of superior gluteal nerve?

A

Root = Sacral plexus, Posterior division (L4,L5,S1)

Supply = Abductors of thigh: Gluteus medius and minimus + Tensor fasciae latae for flexion

No skin innervation

37
Q

Root and supply of Inferior gluteal nerve?

A

Root = sacral plexus, posterior division (L5, S1, S2)

Supply = Gluteus maximus** (medius and minimus are innervated by superior gluteal nerve)

No skin innervation

38
Q

Result of injury to superior gluteal nerve?

A

Paralyzed abductors of thigh and tensor fasciae latae for flexion

Injury on one side = dipping gait, pelvis ‘drops’ to unsupported side = positive Trendelenburg sign***

Injury on both sides = waddling.

39
Q

Result of injury to Inferior gluteal nerve?

A

Injury: Difficulty in standing up from seated position.

Cannot bend down without overbalancing

40
Q

What is the mnemonic for remembering the dermatomes on posterior legs?

A

Stand on S1 (foot)
Lie on S2 (posterior leg)
Sit on S3 (bedpan area)
Wipe S4 (anus, external genitalia)

41
Q

What does knee jerk and ankle jerk test for?

A

Intactness of:

Knee jerk = L3, L4

Ankle jerk = S1

42
Q

Describe the general arrangement of lower limb Myotomes ?

A

spinal centres for joint movements tend to occupy 4 continuous segments in the spinal cord:

upper 2 segments innervating one movement, lower 2 segments innervating the opposite movement.

For lower limb, start from L2 and consider joint movements from proximal to distal

43
Q

List the movements possible at the hip and which spinal centers are tested?

A

L2,3 = Flexion, adduction, medial rotation

L4,5 = extension, ABduction, lateral rotation

44
Q

List the movements possible at the knee and which spinal centers are tested?

A

L3,4 = extension

L5,S1 = flexion

45
Q

List the movements possible at the ankle and which spinal centers are tested?

A

L4,5 = dorsiflexion

S1,2 = plantarflexion

46
Q

List the movements possible at the foot and which spinal centers are tested?

A

L4 = inversion

L5, S1 = eversion

47
Q

Which dermatomes are often affected in sciatica?

A

L4, L5 and S1 dermatomes

often involved in sciatica: e.g. prolapsed vertebral disc leading to loss of sensation

48
Q

Which lumbar plexus nerves pierce the psoas major? Which passes medially and which laterally?

A 
Medial = Obturator n. 
Pierce = Gentiofemoral 
Lateral = Ilioinguinal, Iliohypogastric, Lateral femoral cutaneous n., Femoral n.
49
Q

Define the spinal nerve root of the lumbar plexus branches?

A

2 from 1:

1) Iliohypogastric nerve (L1)
2) Ilioinguinal nerve (L1)

2 from 2:

3) Genitofemoral nerve (L1,2)
4) Lateral cutaneous nerve of thigh (L2,3)

2 from 3:

5) Obturator nerve (L2,3,4)
6) Femoral nerve (L2,3,4)

50
Q

What is innervated by the pudendal nerve?

A

External anal sphincter
External urethral sphincter
Levator ani muscles

Sensory: penis/ clitoris, most of skin of perineum

MBBS II MSS (31 decks)

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