9.11 Nerves of the Lower Limb

Question 1

From what spinal roots does the lumbar plexus derive its supply from?

Answer 1

The lumbar plexus is derived from spinal nerve roots L1-5

Question 2

What are the 6 main terminal branches of the lumbar plexus?

Answer 2

1. Iliohypogastric Nerve
2. Inguinal Nerve
3. Genitofemoral Nerve
4. Lateral Femoral Cutaneous Nerve
5. Obturator Nerve
6. Femoral nerve

(in order of their branching off the plexus)

Question 3

Describe the path of the lumbar plexus nerves from their origin to the lower leg

Answer 3

The lumbar spinal nerves emerge from interverebral foramen and pass down to the periphery and pass into psoas major.

They converge on psoas and reform within the substance of psoas and come out either..

• 4 lateral to psoas
• 1 branch medial to psoas (obturator nerve)
• 1 branch goes through the substance of psoas (genitofemoral)

Question 4

Do the ventral rami or dorsal rami of L1-L4 make up the lumbar plexus?

Answer 4

Only ventral rami of the spinal cord (dorsal rami never form plexuses)

Question 5

What is special about the L2,3,4 divisions of the lumbar plexus?

Answer 5

They have both an anterior and posterior division (like contributions of the brachial plexus of the arm)

(L1 and L5 only have anterior division)

This anatomy relates to embryolgical devleopment.

Question 6

Explain what the anterior division of the Lumbar plexus generally innervates.

Relate this to embryolgical development of the lower limb.

Answer 6

In development, the lower limb is buds out externally rotated and it rotates 90 degrees inwards/medially in utero.

Thus before this rotation happens:

• the adductor muscle compartment is originally anterior, thus this region is supplied by the anterior division.
• the posterior division thus supplies what is now laterally (used to be posterior) which is the abductors (femoral)

Question 7

What does the lumbar plexus innervate?

Answer 7

Lumbar plexus is primarily distributed to the lower limb.

• The termination of thoracic nerve, T12 forms some of the lumbar plexus and also contributes to nerves to the inguinal region
• L1 also supplies the lower abdominal wall

Question 8

Which nerves come out of the following …

• Lateral Border of the Psoas?
• The Anterior Border of Psoas (through it)?
• Medial Border of Psoas?

Draw them coming out

Answer 8

Lateral

• Iliohypogastric (L1)
• Ilioinguinal (L1)
• Lateral Femoral Cutaneous Nerve (L2,3)
• Femoral Nerve (L2,3,4)

Anterior

• Gentiofemoral (L1,2)

Medial

• Obturator (L2,3,4)

Question 9

Describe the path of the nerves coming out of L1

Answer 9

The Ileioinguinal nerve and Ileohypogastric nerves go to the lower parts of the anterior abdominal wall (transverse oblique and transverse abdominus) and the pelvic region

Question 10

What is the relationship between the ileohypogastric nerve and ileoinguinal nerve?

Answer 10

Ileohypogastric is the L1 nerve itself and has the same exit pathway as a typical intercostal nerve.

• It comes out and supplies the skin of the anterior abdominal wall by cutaneous branches

The ileoinguinal nerve it is a colateral branch of the ileohypogastric.

• It itself has no collateral branches emerging from it, thus it doesn’t have cutaneous supply

Question 11

Describe how the lateral femoral cutaneous nerve gets through the pelvis

• What is special about it?
• Describe how pathology can occur to it

Answer 11

It passes…

• Under the inguinal ligament about a 1cm medial to the ASIS.
• It is a purely sensory nerve supplying skin over the lateral aspect of the thigh.
• It is susceptible to compression at the site where it passes under the inguinal ligament particularly during pregnancy, overweight/obese as the increased weight can compress the nerve = MARALGIA PARASTHETICA

Question 12

What makes up the borders of the femoral triangle?

Answer 12

• Laterally Sartorius Muscle
• Anteriorly Inguinal Ligament
• Medially Adductor Longus Muscle

Question 13

There are vascular structures that pass through the femoral triangle on their way to the lower limbs.

What are these structures?

What are they protected by?

Answer 13

Artery, vein and canal - which holds lymph nodes)

They are surrounded by the deep fascia called the femoral sheath

Question 14

How and where does the femoral nerve pass through in the femoral triangle (in relation to the femoral sheath)

Answer 14

The femoral nerve passes into femoral triangle below inguinal ligament. It is lateral to the sheath, NOT inside the sheath.

Question 15

Describe the order of the vessels running through the femoral artery (medially to laterall)

Answer 15

Lateral to Medial:

• Nerve (femoral)
• Artery
• Vein
• (Lymph vessels)

How to remember: “N.A.V.igate” to the good stuff

Question 16

What happens to the femoral nerve as soon as it enters the femoral triangle?

Answer 16

As soon as it enters the triangle (few cm below) it breaks up into its branches most of which are muscular but also some sensory.

This division is into the superficial and deep branches

Question 17

Describe the femoral nerve in terms of:

• What spinal nerve roots
• Anterior or posterior division
• Emergence from Psoas Major Muscle

Answer 17

• L2,3,4
• Posterior Division
• Emerges from the lateral border of psoas

Question 18

What landmark separates the superior branches of the femoral nerve from the deep branches? What does this structure do?

Answer 18

The lateral circumflex femoral artery.

Branches of this artery go up to head of femur to supply the neck.

Question 19

Describe the path of the femoral nerve descending down the leg

Answer 19

The femoral nerve is the largest branch of the lumbar plexus.

• Descends in the abdomen through the psoas major muscle.
• Travels through the pelvis to approximately the mid point of the inguinal ligament. It then traverses under the inguinal ligament into the thigh and splits into an superficial (anterior) and deep (posterior) division.
• It passes through the femoral triangle lateral to the femoral vessels and gives off articular branches to the hip and knee joints.
• These vessels are deeply embedded in the thigh

Question 20

Where is the femoral nerve most suseptible to injury?

Answer 20

Once it gets into the thigh it is embedded in muscle, it most susceptible to injury in the groin as it passes through inguinal ligament.

It is not commonly associated with typical injury but damage to it leads to loss of motor control to quadricepts, lost sensory and diminished patellar tendon reflex.

Question 21

What motor innervation does the femoral nerve supply?

Do these nerves come from the superficial or deep divison?

Answer 21

Femoral supplies motor innervation to the muscles located in the anterior compartment of thigh

• Quadriceps
• Sartorius
• Pectineus

Superficial gives rise to one muscle: sartorius. (Everything else is sensory to the thigh).
Deep branch supplies the remaining muscles of the anterior: quads and pectineus. (And gives off one sensory branch: saphenous nerve) to the medial aspect of leg and foot

Question 22

What sensory innervation does the femoral nerve give?

Do these nerves come from the superficial or deep division?

Answer 22

It supplies sensory innervation to the medial aspect of the thigh via the saphenous nerve

As it crosses the joint, it also supplies articular branches to the hip and knee joint.

Superficial gives rise to one muscle: sartorius. (Everything else is sensory to the thigh).
Deep branch supplies the remaining muscles of the anterior: quads and pectineus. (And gives off one sensory branch: saphenous nerve) to the medial aspect of leg and foot terminating at the first metatartsal-phalageal joint

Question 23

Describe the obturator nerve in terms of…

• Lumber Spinal Roots
• Anterior or posterior division of the plexus
• Origin in relation to psoas
• Its passage through the pelvis to the leg

Answer 23

• L2,3,4
• Anterior divisions
• Medial border of Psoas
• Passes down the lateral wall of pelvis → through the obturator canal → medial compartment of thigh

Question 24

The obturator nerve divides into 2 divisions (Anterior and posterior). What separates them?

What does the nerve supply?

Answer 24

It divides into an anterior and posterior division in relation to ADDUCTOR BREVIS muscle.

• Anterior division supplies motor to the superficial adductor muscles
• Posterior division supplies motor to fibres of the adductor magnus (from both obturator nerve and sciatic nerve)
• Articular branches to the hip

Question 25

What sensory contribution does the obturator nerve supply?

Answer 25

Sensory to the inferomedial thigh just above the knee joint. Thus referred pain of any irritation of the nerve can cause pain in this area of the skin * Eg. Irritation by osteophytes external to the pelvis, inadvertant acetabulum compression * Eg. inflammation of the ovary on the lateral pelvic wall

Question 26

From what spinal nerve roots does the sacral plexus recieve its input from?

Answer 26

The sacral plexus has contirbution from **L4 and L5** to its upper part and from **S1, S2, S3 and S4** to the lower part L4 and L5 make contribution as a large combined nerve called the **lumbrosacral trunk**

Question 27

Where does the lumbosacral trunk (L4/L5) join the S1-S4 spinal nerve roots to form the sacral plexus?

Answer 27

On the surface of the posterior pelvic wall, **anterior to the piriformis muscle**

Question 28

Do all the branches of the sacral plexus supply the lower limb?

Answer 28

No * A branch goes off to supply piriformis itself (not considered part of the lower limb) * Pudendal innervates the lower abdominal muscles and pelvic sphincters as well as sensory to the groin and perineum

Question 29

Describe the Sciatic nerve in terms of: * Nerves roots that supply it * Anterior or posterior divisions of the sacral plexus

Answer 29

* The sciatic nerve is the biggest nerve in the body from L4, 5, S1, 2, 3 (forming within a sheath) * Both anterior and posterior divisions.

Question 30

Describe the path of the sciatic nerve from the plexus down to the limb

Answer 30

* It exits the pelvic cavity via the **greater sciatic foramen (GSF)**. * It emerges **below the piriformis** * This has variation: below piriformis, sometimes pierces it and the common fibular portion through it and join again once it gets through gluteal region. * The nerves pass into the **gluteal region** and pass **behind the hip joint.** * It descends in the **posterior thigh** underneath biceps * It **divides** at the **apex of the popliteal fossa** * Tibial branch (more central/medial and is more larger) * Common fibular branch heads towards the head of the fibula.

Question 31

Describe injury to the sciatic nerve

Answer 31

Sciatic nerve may be injured as a result of posterior dislocation of the hip with force directly along the femor in flexion forcing the hip posteriorly. The most common injury is injection into the wrong quadrant of the gluteal region.

Question 32

Describe the motor innervation of the sciatic nerve

Answer 32

It does _not_ innervate any muscles of the gluteal region. It directly innervates the muscles in the **posterior compartment of the thigh, and the hamstring portion of the adductor magnus.** * Tibial nerve – the muscles of the **posterior leg** (calf muscles), and some of the **intrinsic** **muscles of the foot.** * Common fibular nerve – the muscles of the **anterior leg, lateral leg,** **and the remaining intrinsic foot muscles.** In total, the sciatic nerve innervates the muscles of the posterior thigh, entire leg and entire foot.

Question 33

Describe the sensory innervation of the sciatic nerve

Answer 33

The sciatic nerve does not have any direct cutaneous functions. It provides i**ndirect sensory innervation** via its terminal branches: * Tibial nerve – Innervates the posterolateral and anterolateral sides of the leg, and the sole of the foot * Common fibular nerve – Innervates the lateral leg and the dorsal surface of the foot.

Question 34

Describe the Tibial Nerve in terms of... * Nerve roots from which it emerges * Anterior or posterior divions of the sacral plexus * Path through pelvis to the leg

Answer 34

* From L4, L5 and S1-3 * Anterior divisions * Vertical descent **through** popliteal fossa → **beneath fibrous arch of Soleus** → descends **on Tibialis Posterior in calf** → p**osterior to medial malleolus** → sole of foot → divides into **medial and lateral plantar nerves**

Question 35

What are the medial and lateral plantar terminal divisions of the tibial nerve analogous to (in relation to the upper limb)?

Answer 35

As the tibial nerve descends down the posterior calf and wraps around the medial medial malleolous to divides into these two branches They are analogous to the medial and ulnar nerves of the hand The lateral plantar (ulnar nerve - supplies the deep intrinsic muscles) while the medial plantar supplies halix. Both of these nerves contribute to the skin.

Question 36

Describe the motor innervation of the tibial nerve

Answer 36

Motor to muscles of posterior leg and sole of foot

Question 37

Describe injury to the tibial nerve

Answer 37

Tibulal nerve is the most commonly injured nerve of the lower limb as it pases laterally down. The other nerve passes in an arch in the superficial part of the calf (soleus). It continuous down the back of the leg (posterior tibial nerve) and around the medial medial malleolous and passes underneath the flexor retinaculum in the region of the tarsal tunnel. **Tarsal tunnel syndrome** = entrapment of the posterior tibial nerve under the retinaculum.

Question 38

Describe the common fibular nerve in terms of.. * Spinal nerve roots * Anterior or posterior divison of the sacral plexus * Path through pelvis to the leg

Answer 38

* L4,5, S1-2 * Posterior Divisions * Passes **Medial to Biceps** → **superficial to lateral head of Gastrocnemius** → winds round neck of fibula → Passes into Fibularis Longus muscle → divides into its terminal branches (superfical and deep)

Question 39

Describe the path of the deep vs. the superficial branches of the common fibular nerve

Answer 39

**DEEP** begins in Fibularis longus → descends deep to EDL, anterior to interosseous membrane → beneath extensor retinaculum → dorsum of foot **SUPERFICIAL** descends in lateral compartment supplying Fibularis Longus and Brevis then becomes superficial to supply skin over lower lateral leg and dorsum of foot

Question 40

Describe the sensory innervation of the tibial nerve

Answer 40

Sensory to posterior leg (**sural nerve**) and sole of foot (**medial calcaneal, medial and lateral plantar nerves**) The main cutaneous branch - sural nerve takes sensation from skin of the lateral aspect of the leg and foot and tends to have contribution from both tibial and common femoral branches

Question 41

Describe the motor and sensory nnervation of the deep vs. the superficial divisions of the common fibular nerve

Answer 41

Deep Fibular nerve is motor to **anterior compartment of leg and Extensor Digitorum Brevis** * And sensory innervation into the webspace between the big toe and second digit Superficial Fibular nerve is motor to l**ateral compartment of leg** and sensory to lower lateral leg and dorsum of foot

Question 42

In what situation would the common fibular nerve be injured?

Answer 42

Trauma to the lateral side of the femur endangers the nerve, eg. plaster casts put on too tight. As it supplies anterior muscles (tibialis anterior etc, these muscles dorsiflex the foot). Damage to the nerve causes foot drop (slapping down in locomotion) and tend to see them with high knee lift.

Question 43

Be able to draw the innervation of the basic **muscle groups** of the thigh and leg

Answer 43

* Large muscles in the gluteal region are supplied by the superior and inferior gluteal nerves * Anterior compartment of thigh supplied by femoral nerve * Medial compartment of thigh supplied by obturator nerve * Posterior compartment of thigh and leg, and sole of foot are supplied by tibial part of the sciatic nerve ( except the short head of biceps ) * Anterior and lateral compartments of leg, and dorsum of foot are supplied by common fibular part of the sciatic nerve

Question 44

Be able to draw the sensory innervation of the thigh and leg

Answer 44

* The femoral nerve innervates skin on anterior and medial thigh and medial side of leg and foot * The obturator nerve innervates the medial side of thigh just above the knee * The tibial part of the sciatic nerve innervates posterior leg via the sural nerve and the heel and sole of the foot * The common fibular part of sciatic nerve innervates lateral side of leg and dorsum of foot * The lateral cutaneous nerve of thigh and posterior cutaneous nerve of thigh branch directly from lumbar & sacral plexuses, respectively

Question 45

Draw dermatomes of the lower leg

Answer 45

You stand on S1, you sit on S3, you shit through S4 and what comes out runs down the back of the thigh S2. Lumbar spine may refer pain into the lower limb as this is where segments come from particularly ovary, prostate (into gluteal region)

Question 46

Know the myotomes of the foot

Answer 46