"Review of Nerves and Vessels of the Lower Limb" Questions

Question 1

What can the nervous system of the body be divided into and what does each component contain?

Answer 1

Central nervous system - brain + spinal cord

Peripheral nervous system - cranial + spinal nerves

Question 2

Other than central/peripheral, what other category can the nervous system of the body be divided into and what are the components of each?

Answer 2

Somatic nervous system

• somatic motor (efferent) to skeletal muscle
• somatic sensory (afferent) sensory information from skin + muscle

Autonomic nervous system

• autonomic motor
• autonomic sensory
• this is from/to cardiac and smooth muscle, glands, gut etc

Question 3

How many pairs of spinal nerves are there, what are the divisions of these nerves and what are they formed from?

Answer 3

31 pairs

• 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
• each spinal nerve is formed from a union between an anterior root (motor) and dorsal root (sensory) and the roots merge at the intervertebral foramen to form a spinal nerve

Question 4

Where do autonomic fibres pass, in terms of vertebral levels?

Answer 4

Between T1-L2 and S2-S4

Question 5

Which of the anterior and posterior rami form the major plexi (plexuses) of the limbs?

Answer 5

Anterior rami

• of C4-T1 for upper limb
• of L2-S2/S3 for lower limb

Question 6

What are the 5 main nerves innervating the muscles of the leg and which muscles/compartment do they innervate?

Answer 6

Femoral nerve (L2-L4, posterior fibres) - iliopsoas, anterior compartment of the thigh

Obturator nerve (L2-L4, anterior fibres) - medial compartment of the thigh

Sciatic nerve (L3-S3, anterior + posterior fibres) - posterior compartments of thigh and leg, foot

Superior gluteal nerve (L4-S1) - gluteus medius + minimus, tensor fascia lata

Inferior gluteal nerve (L5-S2) - gluteus maximus

Question 7

What is the principle about muscles with the same action regarding their nervous supply?

Answer 7

If they have the same action on a particular joint, they will have a common nerve supply

Question 8

What is the principle about muscles/muscle groups with opposing actions?

Answer 8

Opposing muscle have nerve supplies 1-2 segments above or below

Question 9

What are the spinal nerve roots for hip flexion/extension, knee flexion/extension, and ankle dorsiflexion/plantarflexion?

Answer 9

Hip flexion - L2, L3
Hip extension - L4, L5
Knee flexion - L5, S1
Knee extension - L3, L4
Ankle dorsiflexion - L4, L5
Ankle plantarflexion - S1, S2

Question 10

How are the spinal nerves divided amongst the areas of the body in terms of where they supply?

Answer 10

C1-C4 - neck
C5-T1 - upper limbs
T2-L1 - trunk
L2-S2 - lower limbs
S2-C1 - perineum

Question 11

What is the peripheral innervation for the lower limb derived from and what is this structure derived from?

Answer 11

Derived from the lumbo-sacral plexus

- lumbo-sacral plexus is derived from the anterior rami of the lumbar and sacral spinal nerves

Question 12

What are the 6 branches of the lumbar plexus and their spinal roots?

Answer 12

Iliohypogastric and ilio-inguinal (L1)
Genitofemoral (L1, L2)
Lateral cutaneous nerve of the thigh (L2, L3)
Femoral nerve (L2, L3, L4, posterior divisions)
Obturator nerve (L2, L3, L4, anterior divisions)
Lumbosacral plexus (L4, L5 - feeds sacral plexus)

Question 13

What are the 8 branches of the sacral plexus and their spinal roots?

Answer 13

Sciatic nerve (L4, L5, S1, S2, S3)
Nerve to piriformis (S1, S2)
Posterior cutaneous (S1, S2, S3)
Pelvic splanchnic (S2, S3, S4 - parasympathetic)
Pudendal (S2, S3, S4)
Nerve to obturator internus (L5, S1, S2)
Superior gluteal (L4, L5, S1)
Inferior gluteal (L5, S1, S2)

Question 14

What motor and sensory innervations does the femoral nerve provide and what does it terminate as?

Answer 14

Motor - iliopsoas and anterior thigh muscles
Sensory - front of the thigh

Terminates as the saphenous nerve (sensory to medial aspect of the leg)

Question 15

What motor and sensory innervations does the ubturator nerve provide?

Answer 15

Motor - supplies the adductor (medial compartment) muscles of the thigh
Sensory - medial aspect of the thigh (and parts of the pelvis)

Question 16

What motor and sensory innervations does the sciatic nerve supply and how does it branch?

Answer 16

Sciatic nerve proper supplies the hamstring muscles and some sensory branches to the back of the thigh
- passes through greater sciatic foramen into the posterior compartment of the thigh and (just above the knee joint) branches into tibial and common peroneal nerves

Question 17

What motor and sensory innervations does the common peroneal nerve provide and what does it terminate as?

Answer 17

Motor - anterior and lateral compartments of the leg
Sensory - anterior and lateral aspects of the leg and dorsum of the foot

Terminal branches are the superficial and deep peroneal nerves (motor), sural nerve (important sensory branch)

Question 18

What motor and sensory innervations does the tibial nerve provide?

Answer 18

Motor - posterior compartment of the leg and most intrinsic muscles of the foot
Sensory - back of the leg and sole of the foot

Question 19

Nerve function (and its impairment) can be assessed by 5 modalities, what are they?

Answer 19

Motor
Sensory
Reflex
Autonomic (like sweat etc)
Trophic (growth/cellular damage)

Question 20

As an example, describe the nerve function after damage to the common peroneal nerve at the level of the fibular neck (very common place for it to be damaged).

Answer 20

Motor - foot drop, loss of muscle action in anterior and lateral compartments of the leg
Sensory - loss of sensation in the distribution of the common peroneal nerve i.e. the dorsum of the foot at least
Reflex - no loss of reflexes as ankle jerk reflex is innervated by the tibial nerve
Autonomic - abnormalities of sweating in the cutaneous distribution of the common peroneal nerve
Trophic - in chronic cases there may be damage to the sole of the foot due to the pressure effects of the foot drop

Question 21

How likely is the femoral nerve to get injured and what can injure it?

Answer 21

Rarely damage except iatrogenically

• commonest injury is via traction injuries during hip replacements and laparoscopic repairs of inguinal hernias
• can be damaged during erroneous attempted cannulations of the femoral artery/vein

During surgery or poor cannulation of femoral artery/vein

Question 22

How likely is the lateral cutaneous nerve of the thigh to get injured and what can injure it?

Answer 22

Fairly unlikely
Superficial nerve that passes 2cm medial to the ASIS at the level of the inguinal ligament
- can be compressed at this level causing Bernhardt-Roth syndrome
- BR syndrome is numbness/pain in the outer thigh caused by nerve injury rather than trauma to the thigh

Question 23

How likely is the obturator nerve to get injured and what can injure it?

Answer 23

Rarely damaged

- pain in the distribution of the obturator nerve can be indicative of malignant pelvic disease

Question 24

How likely is the superior gluteal nerve to get injured and what can injure it?

Answer 24

Fairly uncommon

• commonest injury is in hip replacement
• leads to Trendelenberg’s gait due to loss of gluteus medius/minimus muscles

Question 25

How likely is the sciatic nerve to get injured and what can injure it?

Answer 25

Fairly uncommon - commonest cause is after hip replacement - common peroneal division is more at risk than the tibial division - sciatic nerve can be damaged at the hip by erroneous IM injection (remember use safe quadrant) - less common causes are hip dislocations/acetabular fractures (trauma), and pelvic disease

Question 26

Where can the common peroneal nerve get injured and what can injure it?

Answer 26

Can be damaged at the level of the hip and highly vulnerable at the level of fibular neck (wraps around it) - causes of damage include trauma, knee replacement and external pressure (e.g. during surgical procedure)

Question 27

How likely is the tibial nerve to get injured?

Answer 27

Rarely damaged in isolation as it is very deep | - only really going to get damaged if sciatic nerve is damaged at the hip

Question 28

How likely is the saphenous nerve to get injured and what can injure it?

Answer 28

Commonly injured | -- can be damaged at the medial malleolus or at the level of the knee (e.g. ACL surgery)

Question 29

What are nerve blocks and what are they used for?

Answer 29

Nerve blocks can be utilised by anaesthetists to aid or substitute general anaesthesia during surgery

Question 30

What are some examples of nerve blocks in the lower limb?

Answer 30

Femoral nerve blocks Sciatic nerve blocks Ankle blocks Blocks of the lateral cutaneous nerve of the thigh

Question 31

How does the anaesthetist determine the best place to insert local anaesthetic?

Answer 31

Knowledge of peripheral anatomy | - allows to localise best place to put it and predict the level and extent required

Question 32

Summarise the arterial supply of the thigh. (write it out on a piece of paper)

Answer 32

Aorta splits into the common iliac arteries at L4 Common iliac arteries bifurcate at the pelvic brim into the internal iliac artery (gives off obturator artery) and external iliac artery External iliac artery becomes the femoral artery at the inguinal ligament Femoral artery passes underneath the inguinal ligament at the mid-inguinal point Just underneath the inguinal ligament it has four branches; superficial circumflex iliac artery, superficial epigastric artery, superficial external pudendal artery, deep external pudendal artery The femoral artery continues downward and gives off the profunda femoris artery before itself becoming the superficial femoral artery The femoral artery enters the adductor canal and becomes the popliteal artery The popliteal artery bifurcates at the distal end of the popliteal fossa into the anterior and posterior tibial arteries

Question 33

Summarise the arterial supply to the leg. (also write this down on a piece of paper then summarise the whole lower limb)

Answer 33

The anterior tibial artery passes into the anterior compartment of the leg, running on the interosseous membrane. - at the level of the foot, the anterior tibial artery becomes the dorsalis pedis artery The posterior tibial artery passes into the posterior compartment of the leg alongside tibialis posterior - it passes behind the medial malleolus and enters the foot before dividing into the MEDIAL and LATERAL PLANTAR arteries - the posterior tibial artery gives off a branch called the peroneal artery which supplies the lateral compartment of the leg

Question 34

Briefly summarise the superficial veins of the lower limb.

Answer 34

Dorsal venous arch receives most of the blood from the foot Long saphenous vein starts from the medial portion of the dorsal venous arch of the foot and runs up the medial aspect of the leg Short saphenous vein starts from the lateral aspect of the dorsal venous arch of the foot Both saphenous veins communicate until short saphenous vein ends by draining into popliteal vein (deep system) The long saphenous vein eventually (at the sapheno-femoral junction) drains into the femoral vein (deep system) There are a multitude of important veins that act as a passage for blood to move from the superficial veins to the deep veins - these are the PERFORATING veins Junctions with these veins have valves to prevent back flow of blood from deep to superficial systems - faulty in varicose veins

Question 35

Briefly summarise the deep veins of the lower limb.

Answer 35

The deep veins lie within the deep fascia and generally run alongside the arteries. They have valves to prevent back flow of blood. The venae comitantes of the anterior/posterior tibial arteries and the popliteal artery form the popliteal vein. The deep veins are mainly within muscle, and the "muscle pump" contributes towards the venous return from the lower limb to the abdomen. The popliteal vein receives the short saphenous vein at the popliteal fossa. Popliteal vein eventually becomes the femoral vein Just proximal to the inguinal ligament, the profunda femoris veins and then the long saphenous vein join the femoral vein. Once the femoral vein has passed the inguinal ligament it comes the external iliac vein.

Question 36

What is the anatomy of the femoral sheath and what structures lie where?

Answer 36

Femoral sheath encloses the femoral vessels distal to the inguinal ligament - femoral artery is always lateral to the femoral vein

Question 37

Where would you palpate the femoral artery pulse?

Answer 37

Mid-inguinal point

Question 38

Where would you palpate the popliteal artery pulse?

Answer 38

Inferior part of the popliteal fossa, against the posterior surface of the tibia

Question 39

Where would you palpate the posterior tibial artery pulse?

Answer 39

Behind medial malleolus

Question 40

Where would you palpate the dorsalis pedis artery pulse?

Answer 40

Dorsum of foot, lateral to extensor hallucis longus tendon