9.11 Nerves of the Lower Limb Flashcards
• The origin of the lumbosacral plexus and the formation of its major branches • The origin, course and distribution of the sciatic, femoral, obturator, common fibular and tibial nerves including the muscles and muscle groups that each supplies and their sensory distribution • The common sites of peripheral nerve injury and the possible functional effects of such damage • The dermatomes and myotomes of the lower limb
From what spinal roots does the lumbar plexus derive its supply from?
The lumbar plexus is derived from spinal nerve roots L1-5
What are the 6 main terminal branches of the lumbar plexus?
- Iliohypogastric Nerve
- Inguinal Nerve
- Genitofemoral Nerve
- Lateral Femoral Cutaneous Nerve
- Obturator Nerve
- Femoral nerve
(in order of their branching off the plexus)
Describe the path of the lumbar plexus nerves from their origin to the lower leg
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)
Do the ventral rami or dorsal rami of L1-L4 make up the lumbar plexus?
Only ventral rami of the spinal cord (dorsal rami never form plexuses)
What is special about the L2,3,4 divisions of the lumbar plexus?
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.
Explain what the anterior division of the Lumbar plexus generally innervates.
Relate this to embryolgical development of the lower limb.
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)
What does the lumbar plexus innervate?
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
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
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)
Describe the path of the nerves coming out of L1
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
What is the relationship between the ileohypogastric nerve and ileoinguinal nerve?
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
Describe how the lateral femoral cutaneous nerve gets through the pelvis
- What is special about it?
- Describe how pathology can occur to it
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
What makes up the borders of the femoral triangle?
- Laterally Sartorius Muscle
- Anteriorly Inguinal Ligament
- Medially Adductor Longus Muscle
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?
Artery, vein and canal - which holds lymph nodes)
They are surrounded by the deep fascia called the femoral sheath
How and where does the femoral nerve pass through in the femoral triangle (in relation to the femoral sheath)
The femoral nerve passes into femoral triangle below inguinal ligament. It is lateral to the sheath, NOT inside the sheath.
Describe the order of the vessels running through the femoral artery (medially to laterall)
Lateral to Medial:
- Nerve (femoral)
- Artery
- Vein
- (Lymph vessels)
How to remember: “N.A.V.igate” to the good stuff
What happens to the femoral nerve as soon as it enters the femoral triangle?
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
Describe the femoral nerve in terms of:
- What spinal nerve roots
- Anterior or posterior division
- Emergence from Psoas Major Muscle
- L2,3,4
- Posterior Division
- Emerges from the lateral border of psoas
What landmark separates the superior branches of the femoral nerve from the deep branches? What does this structure do?
The lateral circumflex femoral artery.
Branches of this artery go up to head of femur to supply the neck.
Describe the path of the femoral nerve descending down the leg
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
What sensory innervation does the femoral nerve give?
Do these nerves come from the superficial or deep division?
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
The obturator nerve divides into 2 divisions (Anterior and posterior). What separates them?
What does the nerve supply?
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
What sensory contribution does the obturator nerve supply?
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
From what spinal nerve roots does the sacral plexus recieve its input from?
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
Where does the lumbosacral trunk (L4/L5) join the S1-S4 spinal nerve roots to form the sacral plexus?
On the surface of the posterior pelvic wall, anterior to the piriformis muscle
Describe the Sciatic nerve in terms of:
- Nerves roots that supply it
- Anterior or posterior divisions of the sacral plexus
- 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.
Describe the path of the sciatic nerve from the plexus down to the limb
- 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.
Describe the sensory innervation of the sciatic nerve
The sciatic nerve does not have any direct cutaneous functions. It provides indirect 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.
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
- From L4, L5 and S1-3
- Anterior divisions
- Vertical descent through popliteal fossa → beneath fibrous arch of Soleus → descends on Tibialis Posterior in calf → posterior to medial malleolus → sole of foot → divides into medial and lateral plantar nerves
What are the medial and lateral plantar terminal divisions of the tibial nerve analogous to (in relation to the upper limb)?
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.
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
- 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)
Describe the sensory innervation of the tibial nerve
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
Describe the motor and sensory nnervation of the deep vs. the superficial divisions of the common fibular nerve
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 lateral compartment of leg and sensory to lower lateral leg and dorsum of foot
Draw dermatomes of the lower leg
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)
Know the myotomes of the foot
