L9.3 Nerves of the LL

Question 1

Lumbar Plexus

Answer 1

• Lumbar plexus: L1-4
• Major terminal branches emerges from the borders of psoas (landmark)
• LAT:
  
  • Iliohypogastric (comes before), ilioinguinal: L1 → quadratus lumborum → innervation fo ANT ab walls
  • LAT femoral cutaneous (L2,3): Under LAT edge of inguinal lig → ASIS → along LAT cutaneous tissues
  • Femoral N (L2,3,4)
• ANT:
  
  • Genitofemoral N (L1,2)
  • Genital branches & femoral branches → beneath inguinal lig → supply skin of femoral triangle
• MED:
  
  • Obturator

Question 2

Sacral plexus

Answer 2

• Sacral plexus: S1-4 (lumbosacral L4,5)
• Lumbosacral trunk joins S1-4 on piriformis (landmark)
• POS cutaneous nerve of the thigh

Question 3

Gluteal N

Answer 3

• Sup gluteal N (Med & mins) Above
• INF gluteal N (Max) Below (&Sciatic)

Question 4

Femoral Triangle

Answer 4

Femoral (N,A,V(Y))

Femoral sheath encloses A & V

• SUP: IL
• MED: ADD Longus
• LAT: Sartorius
• FLOOR: Pectineus
• ROOF: Fascia Lata

Question 5

Femoral N

Answer 5

• LAT psoas → groove of iliopasoas → beneath I.L → into ANT thighs
• Divides into all terminal branches approx 2.5cm below I.L ∴ hard to damage nerve
• Structure order: N A V (Y)
  
  • Structures (except N) enclosed in femoral sheath
• Motor: ANT thigh muscles (pectineus, satorius, quads)
• Sensory: Anteromedial thigh & MED side of knee, leg & ankle
  
  • ANT Cutaneous branches (MED & intermediate)
  • Saphaneous N → MED leg & foot up to 1st MTP joint
• Articular → hip & knee

Question 6

Obturator N

Answer 6

• Obturator N (L2,3,4) ANT division of ventral rami
• MED of psoas → LAT pelvis → obturator canal → MED thigh
• Motor: Adductors (Pectineus from obturator & femoral; NOT hamstring part of adductor magnus)
• Sensory: Inferomedial thigh (gap which is not covered by the femoral N)
  
  • Could have referred pelvic pain to thigh
• Articular → branches hips

Question 7

Sciatic N

Answer 7

• ANT & POS division (*S4 → peroneum)
• Exit pelvis via greater sciatic foramen → beneath piriformis → POS to hips → descends POS thigh → divides at apex of popliteal fossa into tib & common fibular branches
• Motor: Hamstring → all tibial except for Biceps Femoris (short head of biceps (C.F), long head (Tibial)
• Sensory → via terminal branches
• Articular → hip

Question 8

Tibial N

Answer 8

• (L4,5,S1-3) ANT division
• Continues vertical descent through popliteus fossa → beneath arch of soleus → descends on tibialis POS → POS to medial malleous → Sole of foot → MED & LAT plantar N
• Motor: POS leg & Sole of foot
• Sensory: Posterolateral leg & LAT of foot (SURAL N) & sole of foot (MED calcaneal, MED & LAT plantar N)

Question 9

Common Fibular N

Answer 9

• Common Fibular N (L4,5,S1-2) POS divisions
• Med biceps → SUP to LAT head of gastroc → winds round neck of fibular → Fibularis longus → 2 terminal branches
• Sensory: to upper LAT leg via LAT sural N & gives communicating branch to sural N
• DEEP fib N:
  
  • Motor: ANT leg
  • Sensory: 1st toe cleft (web-space)
• SUP fib N:
  
  • Motor: LAT leg
  • Sensory: LAT leg & dorsum of foot

Question 10

Summary of cutaneous nerve supply

Answer 10

Question 11

Dermatomes

Answer 11

Question 12

Myotomes

Answer 12