Lumbosacral Plexus Cheat Sheet

A Education › Economics cheat sheet in English by immyshah

Anatomy of the lower limb

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PRs

Lateral femoral cutaneous nerve

Nerve Supply	Sensory Innervation
L2 + L3	Skin over anterolateral thigh and lateral knee

This nerve is associated with Meralgia Paresthetica = the compression of the Lateral femoral cutaneous nerve as it passes through the inguinal ligament.
Causes shooting pain down the lateral aspect of the thigh
*Common in gymnasts, scuba divers = when clothing is too tight and compresses inguinal ligament

Sciatic Nerve (Tibial Division)

Nerve Supply	Motor Innervation	Sensory Innervation
L4-S3	Muscles of the posterior thigh (Hamstring muscles: biceps femoris, semimembranosus and semitendinosus) and hamstring portion of adductor magnus + muscles of the posterior leg (Gastrocnemius, Soleus, Tibialis Posterior, Flexor Digitorum Longus, Flexor Hallucis Longus, Popliteus	Innervates the skin of the posterolateral leg, lateral foot and the sole of the foot.

* The primary action of these muscles is PLANTARFLEXION of the foot.
1. Tarsal tunnel syndrome
2. “claw foot” (hyperext MTP, flex IP)
3. Inability to plantar flex and invert = slap

Iliohypogastric Nerve

Nerve Supply	Motor Innervation	Sensory Innervation
L1	Muscles of the abdomen: rectus abdominis, obliques	Skin of suprapubic region

Ilioinguinal nerve

Nerve Supply	Motor Innervation	Sensory innervation
L1	Abdominal muscles: transverse abdominal muscle, internal oblique muscle	Medial thigh and external genitalia

Femoral Nerve

Nerve Supply	Motor Innervation	Sensory Innervation
L2-L4	Innervates the anterior thigh muscles that flex the hip joint (pectineus, iliacus, sartorius) and extend the knee (quadriceps femoris: rectus femoris, vastus lateralis, vastus medialis and vastus intermedius)	Supplies cutaneous branches to the anteromedial thigh (anterior cutaneous branches of the femoral nerve) and the medial side of the leg and foot (saphenous nerve).

Common Fibular/Peroneal Nerve (Sciatic Nerve)

Nerve Supply	Motor Innervation	Sensory Innervation
L4-S2	Short head of biceps femoris. The superficial fibular nerve innervates the muscles of the lateral compartment of the leg; fibularis longus and brevis (foot eversion). The deep fibular nerve innervates the muscle of the anterior compartment of the leg; tibialis anterior, extensor digitorum longus and extensor hallucis longus. These muscles act to dorsiflex the foot and extend the digits. It also innervates some intrinsic muscles of the foot.	Superficial fibular nerve: Innervates the skin of the anterolateral leg, and dorsum of the foot (except the skin between the first and second toes). Deep fibular nerve: Innervates the skin between the first and second toes.

Dysfunction of CFN:
Foot Drop (inability to dorsiflex the ankle)
Presentation
• High stepping gait to prevent scraping toes
• Cant evert foot on uneven surfaces
Causes
Herniated disc compressing L5 = foot drop
Knee dislocation = foot drop
Lateral blow/trauma to the head of fibula= foot drop

Compensate by exaggerated hip and knee flexion (+ external rotation) to avoid dragging the toes along the ground

Genitofemoral Nerve

Nerve Supply	Sensory innervation
L1 + L2	Skin over external genitalia and lateral femoral triangle

Obturator Nerve

Nerve Supply	Motor Innervation	Sensory innervation
L2 - L4	Innervates the muscles of the medial compartment of the thigh (obturator externus, adductor longus, adductor brevis, adductor magnus and gracilis).	the skin of the medial thigh.

Superior Gluteal Nerve

Nerve Supply	Motor Innervation
L4-21	Superior to piriformis and innervates the gluteus medius + minimus and Tensor Fasciae Latae

Inferior Gluteal Nerve

Nerve Supply	Motor Innervation
L5-S2	Exits inferior to piriformis and innervates gluteus maximus muscle only

Posterior Femoral Cutaneous Nerve

Nerve Supply	Sensory Innervation
S1-S3	posterior regions of thigh, proximal part of leg, and skin of perineum

PFCN entrapment has posterior buttocks and thigh pain, from the gluteal fold to the back of the knee

Pudental Nerve

Nerve Supply	Motor Innervations	Sensory Innervation
S2-S4	innervates various pelvic muscles, the external urethral sphincter and the external anal sphincter.	innervates the external genitalia of both sexes and the skin around the anus, anal canal and perineum

A pudendal nerve block is a form of analgesia occasionally given before vaginal childbirth, episiotomy and other minor vaginal procedures.
Epidural targets S2-S4

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