Lower extremity nerves Flashcards
Lumbar plexus origin
Ventral rami T12-L5
Branches of lumbar plexus
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Ileohypogastric nerve
Ileoinguinal nerve
Genitofemoral nerve
Lateral femoral cutaneous nerve
Obturator nerve
Femoral nerve
+/- Lumbosacral trunk
Sacral plexus origin
Forms on anterior belly of piriformis muscle and is formed by lumbosacral trunk (L4-L5) which courses medial to psoas muscle and unites with ventral rami of S1-S4.
12 branches of sacral plexus
Anterior rami give off 6 branches which then divides into anterior and posterior divisions which give off 3 branches each.
Anterior rami: 6 Ps
- Nerve to piriformis (S1-S2)
- Perforating cutaneous nerve (S2-S3)
- Posterior femoral cutaneous nerve (S1-S3)
- Parasympathetic pelvis splanchnic nerves (S2-S4)
- Pudendal nerve (S2-S4)
- Perineal branch of S4 (S4)
Anterior division of anterior rami: Too much Sex IN the Quad
- Tibial portion (L4-S2) of Sciatic nerve (L4-S3)
- nerve to INternal obturator and superior gemellus (L5-S2)
- nerve to Quadratus femoris and inferior gemellus (L4-S1)
Posterior division of anterior rami: CSI
- Common peroneal portion (L4-S2) of sciatic nerve (L4-S3)
- Superior gluteal nerve (L4-S1)
- Inferior gluteal nerve (L5-S2)
Obturator nerve course
From lumbar plexus - provides sensory and motor innervation to thigh. Arises from lumbar plexus on posterior abdominal wall. Root L2-L4
In the pelvis, it descends medial to psoas to obturator canal where it divides into anterior and posterior divisions. The anterior division exits from the canal to enter medial compartment of thigh. Posterior division exits through obturator externus.
In the medial compartment of thigh it divides into anterior and posterior branch separated by adductor brevis
Posterior branch travels under adductor muscle along anterior surface of adductor magnus, innervating obturator externus, adductor brevis and part of adductor magnus that is attached to linea aspera
On anterior surface of adductor brevis the anterior branch goes under pectineus and adductor longus to innervate adductor longus, gracilis, adductor brevis. This branch is often contributed to pectineus muscle. Cutaneous branches innerve skin of medial thigh.
Obturator nerve innervation
Essential to adduction of thigh
Anterior branch - motor to adductor brevis, adductor longus, gracilis and rarely pectinues. Sensory to medial thigh just above medial knee
Posterior branch - adductor magnus, adductor brevis, sometimes adductor longus and obturator externus
Articular branches to hip and knee
Can be entrapped at exit of obturator canal or distally by fascia causing exercise induced medial thigh pain in athletes
Femoral nerve course
Summary - from dorsal divisions of L2-L4 ventral rami. Controls major hip flexor muscles and knee extension muscles. Sensation over anterior and medial thigh as well as medial leg down to the hallux
In pelvis, nerve emerges from behind psoas to run laterally, deep to iliac fascia above ilacus muscle. Muscular branches are first given off to psoas and then to iliacus before nerve runs under inguinal ligament
It enters the thigh. It starts lateral to femoral artery (behind inguinal ligament), dividing approximately 4cm below the inguinal ligament into anterior and posterior divisions.
Anterior division - gives rise to medial and intermediate cutaneous nerves of the thigh and muscular branches to sartorius and pectineus
Posterior division - supplies 4 heads of quadriceps femoris (vastus muscles and rectus femoris) and then continues along medial border of calf as the saphenous nerve
Saphenous nerve is the longest and largest branch of the femoral nerve and supplies skin over medial leg.
Femoral nerve also innervates joint capsule of hip and allows for proprioceptive feedback of the joint
Femoral triangle contents
Femoral nerve - innervates anterior compartment of thigh
Femoral sheath containing femoral artery and branches, femoral vein
Lateral femoral cutaneous nerve
Supplies lateral thigh and is derived directly from lumbar plexus L2-L3 roots.
Travels through pelvis heading towards ASIS and exits lesser pelvis below inginal ligament, anterior to ASIS. Then it bifurcates into anterior and posterior division along length of thigh. Supplies sensory innervation to skin of anterolateral and lateral thigh.
Damage causes Meralgia Paresthetica - usually from entrapment at level of inguinal ligament
Posterior femoral cutaneous nerve
Sensory nerve from sacral plexus. Supplies skin of posterior thigh, butt, posterior aspect of scrotum/labia and variable area of posterior calf
It first appears lateral to anterior sacral foramina under the psoas muscle. Exits pelvis inferior to piriformis via greater sciatic foramen. It then travels with the inferior gluteal artery deep to glut maximus overlying the sciatic nerve. It descends down posterior thigh towards back of knee, deep to fascia lata and superficial to biceps femoris. Once it gets to pop fossa it pierces through deep fascia and travels towards the first half of posterior leg with small saphenous vein. Terminating branches connect to sural nerve.
Pudendal nerve course
From latin for “external genitals” or “parts to be ashamed of”
In summary, its a mixed nerve with sensory, motor and autonomic funcions. Comes from sacral plexus. Main nerve of perineum, pelvic floor muscles and external genitalia.
From sacral plexus S2-S4. Usually associated with internal pudendal artery and vein. It exits pelvis through greater sciatic foramen inferor to piriformis and bends around posterior aspect of sacrospinous ligament
It goes a very short distance within gluteal region where it bends around the sacrospinous ligament to enter perineum through lesser sciatic foramen
While in the gluteal region, it is proximal to ischial spine where it is target of pudendal nerve block.
After exiting lesser sciatic foramen and entering perineum, it passes through sheath of connective tissue on medial wall of obturator internus muscle called the pudendal canal (Alcock’s canal)
It continues through pudendal canal giving off 3 consecutive branches on its path towards pubic symphysis. It gives rise to inferior anal nerve as soon as it enters the canal (AKA inferior rectal nerve). When it gets to distal canal it bifurcates to perineal nerve and dorsal nerve of penis/clitoris.
Sciatic nerve course
Formed from ventral rami L4-S3 and is continuation of upper part of sacral plexus.
It leaves pelvis through greater sciatic foramen, inferior to piriformis and descends btw greater trochanter and ischial tuberosity. Initially deep to piriformis, it runs inferiorly and laterally posterior to ischium, crossing over nerve to quadratus femoris. Below piriformis it is deep to glut maximus. It passes beneath obturator internus, the gemelli and quad femoris.
Nerves branch off to hamstring muscles. Nerve ends at upper aspect of popliteal fossa where it branches to distal nerves (tibial and common peroneal nerve)
Prior to diverging, the tibial and common peroneal nerves are structurally separate and only loosely held together as the sciatic nerve. The tibial nerve is derived from anterior divisions of sacral plexus and the common peroneal nerve is from posterior divisions of the plexus.
Sciatic nerve innervation
Motor
- Hamstrings - biceps femoris, semitendinosus, semimembranosus
- adductor magnus, ischial head
- Indirectly innervates (vis common peroneal and tibial nerves) all muscles of leg and foot
Sensory
- indirectly innervates skin of lateral leg, heel, and both dorsal/plantar foot surfaces
Tibial nerve innervation
Motor
- At popliteal fossa, branches supply medial and lateral gastroc, soleus, plantaris and popliteus muscles
- Popliteus branch goes on to supply tibialis posterior muscle, superior and inferior tibiofibular joint, tibia and interosseous membrane of leg
- Posterior branches of tibial n supply tibialis posterior, flexor dig longus, FHL, and deep part of soleus
Sensory
- Medial sural nerve supplies skin on lower half back of leg and skin of lateral foot/little toe
- medial calcaneal nerve supplies skin on posterior and inferior surface of calcaneus
- articular branches are to the knee and ankle
Branches of tibial nerve
At the foot (just after heel), it divides into medial plantar nerve and lateral plantar nerve. MPN supplies muscular branches to big toe and the 2 toes next to it. LPN gets the other 2 toes.
The sural nerve is a cutaneous branch of the tibial nerve that supplies the skin of legs and feet
Common peroneal nerve innervation
Motor
- Short head of biceps femoris
- terminal branches
- superficial peroneal nerve - lateral compartment of leg - peroneous longus and brevis (evert the foot)
- Deep peroneal nerve - anterior compartment of leg - tibialis anterior, extensor dig longus, extensor hallucis longus (dorsiflex foot and extend digits)
Sensory
- two cutaneous branches arise directly from common peroneal nerve as it moves over lateral head of gastroc
- sural communicating nerve - combines with branch of tibial nerve to form sural nerve (a purely sensory nerve) to go to skin of posterolateral leg
- lateral sural cutaneous nerve - skin of upper lateral leg
- superficial peroneal nerve - skin of anterolateral leg, dorsum of foot (NOT skin btw 1st and 2nd toes)
- deep peroneal nerve - skin between first and second toes
