Week 4 - Lower limb + nerves Flashcards
What are the roots of the lumbosacral plexus made of?
Ventral rami of the spinal nerve:
Lumbar - L2, L3 and 1/2 L4
Sacral - 1/2 L4, L5, S1, S2, S3
Where is the lumbar plexus?
Within the psoas muscle
Where do branches of the lumbar plexus emerge? What are the nerves that emerge?
From psoas major
Femoral nerve
Obturator nerve
Lateral cutaneous nerve
Which roots supply fibres to femoral?
Anterior compartment of the thigh
L2-4
Which roots supply fibres to obturator?
The medial compartment i.e. adductors
L2-3
What does the femoral nerve supply?
The whole anterior compartment of the leg:
Emerges lateral to psoas, supplies:
iliacus, then passes under inguinal ligament and supplies the quadriceps muscles and the sartorius.
Also supplies the cutaneous area
What does the obturator nerve supply?
Medial compartment of thigh:
After emerging medial to psoas, moves along pelvic wall and supplies the three adductors, gracilis and obturator externus
Where is the cutaneous area supplied by the femoral nerve?
Along the front of the thigh - the cutaneous femoral nerve splits into the intermediate and medial cuteneous nerves
Also has the saphenous nerve as one of the femoral nerves cutaneous branches
What does the saphenous nerve supply?
The area medial to the knee, leg and ankle, right down to the instep
Where do all nerves of the sacral plexus exit from?
The greater sciatic foramen
What are the four main nerves from the sacral plexus?
Inferior and superior gluteal nerves
Sciatic nerve
Posterior cutaneous nerve of the thigh
Describe the sciatic nerve
Emerges below the piriformis, and is essentially two nerves covered by a sheath
Branches into the tibial nerve (L4-S3) and the common fibular nerve (L4-S2)
This branching usually occurs 2/3 down the thigh
What general areas does the tibial nerve innervate?
Posterior compartment of the leg, and the foot –> plantar aspect
What general area does the common fibular nerve innervate?
The anterior and lateral compartments of the leg, and the extensors Digitorum/hallucis brevis
Describe the tibial nerves route through the thigh/leg
Midline course through the thigh, passes through the popliteal fossa
Runs deep to soleus
Crosses ankle medially
What are the specific muscles/areas the tibial nerve innervates?
The flexor compartments of the thigh and leg:
- Hamstrings
- Gastrocnemius-soleus, the long flexors of the toes, tibialis posterior and popliteus
- Muscles and skin of the medial and lateral plantar of the sole of the foot
Where does the inferior gluteal nerve go?
To gluteus maximus
WHat is the course of the fibular nerve down the thigh/leg?
Has a variable beginning
Courses laterally and then crosses the neck of the fibula
Then divides into superficial and deep ficular nerve
What does the superficial fibular nerve innervate?
- The lateral compartment of the leg (fibularis longus & fibularis brevis)
- Skin of the anterolateral aspect of the leg
- Dorsum of the foot - except web of big toe
What does the deep fibular nerve innervate?
- The anterior compartment of the leg, and the extensor breves of the foot
- The skin of the first web of the toes
What are the four arteries of the lower limbs?
Femoral (main)
Gluteal arteries
Obturator arteries
Profunda femoris artery
What is the course of the femoral artery?
- Down the front of the thigh, through the adductor magnus
- Turns into popliteal artery, which divides into anterior and posterior tibial arteries
- The anterior tibial artery turns into dorsalis pedis, the dorsal artery of the foot
- Posterior tibial artery goes to the sole of the foot
What is femoris profunda and what does it do?
It is the deep artery of the thigh, found high in the thigh
Supplies the hamstring muscles
What supplies blood to the head of the femur?
The trochanteric anastomosis
Describe the trochanteric anastomosis
This supplies blood to the head of the femur along the reflected part of the capsule
Why are fractures of the femur so detrimental?
Disrupts the anastomosis aka blood supply to the femoral head –> avascular necrosis
In which joints of the lower limb do you find anastomoses?
Hip, Knee and Ankle
Where are the three palpable arterial pulses in the lower limb?
Popliteal
Posterior tibial - half way between medial malleolus and the heel
Anterior tibial/dorsalis pedis - lateral to the FHL tendon, between bases of M1 and M2
Where does the lateral cutaneous nerve of the thigh get entrapped? What would this feel like?
By the inguinal ligament
Pain radiates down the lateral side
Where does the fibular nerve/s get trapped?
Around the neck of the fibula. Can be a result of a blow to the bony prominence, or by a plaster after broken leg
What is the main symptom of an entrapped fibular nerve/s?
Paralyzed dorsiflexors –> foot drop
What is compartment syndrome?
Injury/bleeding into spaces with tight fascia causes an increase in pressure that can affect both nerves and blood vessels
This causes compartment syndrome –> sensory features + motor loss
Vascular disturbance is more serious
What are the two main movements that cycle through walking?
- Stance - limb stationary and bearing weight
- Swing - limb moves forwards
Describe ‘mid-stance’
Knee joint is locked out for stability, while the other limb is off the ground
There is pelvic tilt towards the unsupported side, while the gluteus medius holds the pelvis
Describe ‘take-off’
The swinging leg makes contact with the ground in ‘heel-strike’
The gastrocnemius-soleus, tibialis posterior and FHL propel you forwards,, off the supporting leg
The hip joint carries the whole limb forwards - hip flexors have a role
Describe the ‘swing’ phase of walking
There is hip flexion, knee flexion and ankle dorsiflexion - these carry the leg forwards, and ensure the foot isn’t caught on the ground
Describe the ‘end-of-swing’ phase of walking
There’s knee extension, and hamstrings counteract hip flexion, ‘braking’ the swing
How does the leg prepare for heel strike?
Foot dorsiflexors contract, preventing the foot from flapping
What happens after heel strike?
The dorsiflexors straighten the limb at the ankle, acting as a fixed distal attachment
What happens to the stance phase of walking if gluteus medius is lost?
The pelvis sags to the opposite side in stance phase, and the patient may compensate by tilting to the normal side during walking
WHat would happen to someone’s walk if dorsiflexors are lost?
There would be difficulty clearing the ground –> high step to compensate, and the toes would hit the ground with a ‘flap’ on heel strike
What would happen to walking if hamstrings were lost?
The swing phase would not be arrested, causing the leg to overshoot, and gravity would bring the heel sharply down at the heel strike
