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Lumbosacral Plexus Cheat Sheet by

Anatomy of the lower limb

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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