MSS17 Lumbosacral Plexus And Nerve Distributions Flashcards
Lower limb
Entirely innervated by branches of Lumbosacral plexus
except some skin of buttock: supplied by segmental nerves: posterior rami of upper lumbars and upper sacrals
Lumbar plexus
L1-L4
Location:
- ***within Psoas major muscle
Muscles:
- ***Psoas major
- ***Front of thigh
- ***part of Lower abdominal wall
Main branches:
- Iliohypogastric nerve (L1) (supply skin)
- lateral branch supplies upper lateral quadrant of buttock skin - Ilioinguinal nerve (L1) (supply skin)
- skin below medial part of inguinal ligament and external genitalia - Genitofemoral nerve (L1-2) (supply skin)
- femoral branch supplies area of skin over femoral triangle - Lateral cutaneous nerve of thigh (L2-3) (supply skin)
***5. Femoral nerve (L2-4)
***6. Obturator nerve (L2-4)
Sacral plexus
L4-S4
Location:
- surface of ***Piriformis muscle (lateral rotator of hip)
Muscles:
- ***Buttock
- ***Posterior thigh
- ***Entire leg and foot (except area of skin supplied by saphenous nerve)
- ***Perineum
- ***Pelvic diaphragm (pudental nerve)
Branches that supply lower limb:
- **1. Sciatic nerve
- exit via Greater sciatic foramen
***2. Superior + Inferior gluteal nerves (supply buttock)
- Nerve to Piriformis (supply buttock)
- Nerve to Quadratus femoris (supply buttock)
- Nerve to Obturator internus (supply buttock)
- Posterior cutaneous nerve of thigh (supply skin)
Exit of nerves around pelvis
3 locations:
- ***In front of hip bone (e.g. Femoral nerve)
- ***Obturator foramen (e.g. Obturator nerve)
- ***Greater sciatic foramen (e.g. Sciatic nerve)
***Main nerves of lower limb
- Femoral nerve
- Muscular nerve to Anterior thigh
- Medial and Intermediate Cutaneous nerve of thigh
- Saphenous nerve - Obturator nerve
- Sciatic nerve
- Tibial nerve
- Common peroneal nerve - Superior gluteal nerve
- Inferior gluteal nerve
Femoral nerve
Posterior division (supply前面): L2-4
Location:
- breaks into branches when entering thigh
Branches:
1. Muscular nerve to muscles of Anterior thigh (extensors)
—> Iliacus (anterior hip)
—> Pectineus (medial adductor group of thigh)
—> Sartorius (anterior thigh)
—> Quadriceps femoris (anterior thigh)
- Medial, Intermediate thigh (Medial and Intermediate Cutaneous nerve)
(Lateral cutaneous nerve of thigh NOT a branch of femoral nerve) - Saphenous nerve (longest branch)
- Skin of Medial side leg + foot
Injury:
- paralysed Quadriceps femoris
- unstable knee —> difficulty in walking / standing (個人傾前行)
- sensory loss
Obturator nerve
Anterior division: L2-4
Location:
- deeply between Psoas major and Pelvic brim
- enter thigh through ***Obturator foramen
Muscle: - Medial adductors of thigh —> Gracilis —> Adductor brevis —> Adductor longus —> Adductor magnus (Adductor part) —> Obturator externus
Skin:
- small area of Medial thigh
Injury:
- Limb tends to swing out during walking (abducting)
Sciatic nerve
L4-S3
Surface anatomy: In between - PSIS - Ischial tuberosity - Greater trochanter
Location:
- leaves pelvis through Greater Sciatic notch at a point 1/3 between PSIS and ischial tuberosity (畫一條垂直線分3份)
- leaves buttock midway between midway between ischial tuberosity and greater trochanter
- 87.5% people Sciatic nerve goes below piriformis, 12% pierce through piriformis, 0.5% goes above piriformis
- **- divide into Tibial and Common Peroneal nerve at 2/3 down the thigh
- **Branches:
1. Tibial nerve
2. Common Peroneal nerve
Muscles:
- ***Hamstrings
- ***All muscles in Leg and Foot
Injury:
- Paralysis of all muscles in leg and foot
- Sensory loss in those regions except medial side
- If lesion above origin of branches supplying hamstrings —> limb not able to bear weight / used for walking
Tibial nerve (branch of Sciatic nerve)
Anterior division: L4-S3
Muscles:
- ***Hamstrings except short head of biceps femoris (by Common Peroneal nerve)
- ***Posterior leg
- ***Plantar muscles (Medial and Lateral Plantar nerve)
Skin:
- Posterolateral side of leg
- Lateral border of foot (Sural nerve)
- ***Sole of foot (Medial and Lateral Plantar nerve)
Injury:
- Paralysed Soleus and Gastrocnemius
- Paralysed limb leading when walking (永遠係前面)
- Rigid inelastic foot
- Sensory loss in sole
Common Peroneal nerve (branch of Sciatic nerve)
Posterior division: L4-S2
Location:
- runs along margin of Biceps femoris —> winds around neck of fibula (vulnerable here) —> divides into Superficial and Deep peroneal nerves
Muscles:
- Anterior leg (Dorsiflexors of ankle / Extensors of toes) (Deep peroneal nerve)
- Lateral leg (Everters) (Superficial peroneal nerve)
- Short head of Biceps femoris
Skin:
- Lateral leg (Superficial peroneal nerve)
- ***Dorsum of foot (Superficial peroneal nerve)
Injury:
- Foot drop (∵ cannot Dorsiflex)
Superior gluteal nerve
Posterior division: L4-S1
Muscles: - ***Abductors of thigh —> ***Gluteus medius —> ***Gluteus minimus —> Tensor fasciae latae
Skin:
- NONE
Injury:
- on one side: dipping gait, positive ***Trendelenburg sign (pelvis drops to unsupported side, lesioned side swing outward)
- on both sides: waddling (企鵝行)
Inferior gluteal nerve
Posterior division: L5-S2
Muscles:
- ***Gluteus maximus
Skin:
- NONE
Injury:
- difficulty in getting up from seated position
- cannot bend down without overbalancing
***Summary of thigh muscle innervation
Anterior / Knee extensors:
Femoral nerve
Posterior / Knee flexors:
Sciatic nerve
Medial / Adductors of hip:
Obturator nerve
Lateral / Abductors of hip:
Superior gluteal nerve
(Pectineus, Adductor magnus: hybrid muscles —> located in-between compartments —> dual nerve supply
Pectineus: Femoral + Obturator
Adductor magnus: Obturator + Sciatic)
***Summary of leg muscle innervation
Anterior / Extensors:
Deep Peroneal nerve
Anterolateral / Everters:
Superficial Peroneal nerve
Posterior:
Tibial nerve
***Dermatomes
***Stand on S1, Lie on S2, Sit on S3, Wipe S4
L1: pubic area L2: anterior thigh L3: knee L4: medial leg L5: lateral leg + medial foot S1: lateral foot S2: posterior leg + posterior thigh S3: buttock S4: anal area
**L4, L5, S1: often involved in **Sciatica
