Sacral plexus and derivative nerves, muscles, and lesions of the lower extremity 

This is a brief video on the neuromusculature of lower extremity, specifically the sacral plexus and derivative nerves, muscles, and lesions of the lower extremity.
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Superior gluteal n. (L4-S1)
(thru greater sciatic foramen above piriformis) hip abductors: tensor fascia lata, gluteus minimus, gluteus medius - stabilize pelvis during gait
Inferior gluteal n. (L5-S2)
(thru greater sciatic foramen below piriformis) gluteus maximus - extend and lat rot hip (stand from sit)
Posterior femoral cutaneous n. (S1-S3)
Thru GSF below piriformis→sensory to posterior thigh region
Pudendal n. (S2-4)
Exits GSF below piriformis, enters ISF
Innervates perineum thru pudendal canal
Nerve to quadratus femoris
Nerve to obturator internus
Sciatic n. (L4-S3)
(contains tibial nerve and common fibular nerve, usually exits sacrum below piriformis, divides in popliteal region)
Adductor magnus (hamstring portion)
Trendelenburg (gluteal) gait → shift body weight to weak side to swing limb underneath
Lat hip rotate: obturator internus (goes thru LSF) and superior gemellus
Innervate quadratus femoris and inferior gemelli (lateral hip rotators)
Nerve to piriformis
Innervate piriformis (lateral hip rotator)
(L5-S1) Knee flexors, hip extensors: hamstrings (semimembranosus, semitendinosus, biceps femoris (most commonly injured))
Pulled hamstring → sudden acceleration, can tear proximal tendon or avulse bone
Posterior hip dislocation can damage sciatic n. and vessels, causing avascular necrosis → adduct, flex, int rot short leg
Popliteus muscle - unlocks the knee, knee flexor, tendon→ btwn LCL and lat meniscus.
Tibial nerve
Fibular (peroneal) nerve
Superficial fibular nerve
Deep fibular nerve
(thru popliteal fossa) Posterior leg muscles: superficial (S1-2) (plantar flexors of ankle) gastrocnemius (rapid), soleus (slow/powerful), plantaris (proprioceptive); deep (plantarflex ankle, flex toes, invert foot) tibialis posterior (L4-5), flexor digitorum longus (S2-3), flexor hallucis longus (S2-3) → tendons/n. pass thru tarsal tunnel
(L5-S1) Lateral leg muscles (evertors): fibularis longus, fibularis brevis
(L4-S1) Anterior leg muscles (dorsiflexors): tibialis anterior (primary dorsiflexor), extensor hallucis longus, fibularis tertius (everts foot), extensor digitorum longus
Medial plantar nerve
Lateral plantar nerve
Sensory to foot dorsum
Sensory btwn 1st and 2nd toe (flip flops)
Drop foot damage to dorsiflexors: common/deep fibular n. (ie fibula head trauma) or L4-5 herniation, ant compt muscles paralyzed, pts compensate with hyperflexion of hip
14/18 intrinsic plantar foot muscles (S2-3)→lat 1.5 digit sensation
Innervates 4/18 intrinsic plantar foot muscles: flexor digitorum brevis (flex toes 2-5), abductor hallucis, flexor hallucis brevis (flex proximal phalanx hallux, 1st (medial) lumbrical (flex toes) (all S2-3) → medial 3.5 digits
Diabetic neuropathy → LoF of peripheral sensory nerves → foot ulcers → bacterial infxn → amputation