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LOWER LIMB ANATOMY - COMPLETE MS1 STUDY GUIDE

Gray's Anatomy for Students / KLM Oriented Anatomy Reference

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1. TOPOGRAPHIC ANATOMY & NOMENCLATURE

• Gluteal region - posterolateral to pelvis
• Thigh - between hip and knee (femur region)
• Popliteal fossa - diamond-shaped space behind the knee
• Leg - between knee and ankle (tibia + fibula)
• Foot - divided into dorsum and sole (plantar surface)

1. Anteriorly via femoral triangle (beneath inguinal ligament) - femoral nerve, artery, vein
2. Posteriorly continuous with gluteal region - sciatic nerve
3. Medially via obturator canal - obturator nerve and vessels

• Anterior = Femoral nerve (extension)
• Posterior = Sciatic nerve (flexion)
• Medial = Obturator nerve (adduction)

Mnemonic: "FAS" (Femoral-Anterior, Sciatic-posterior, Obturator-medial) = FAnS

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2. DEEP FASCIA OF THE THIGH, ILIOTIBIAL TRACT & SAPHENOUS OPENING

Fascia Lata

• Divides the thigh into compartments via intermuscular septa that attach to the posterior femur
• Particularly thick laterally where it forms the iliotibial tract (IT band)

Iliotibial Tract (IT Band)

• A thick tendinous band running down the lateral thigh
• Formed by: Tensor fasciae latae + Gluteus maximus both insert into it
• Attaches below to the lateral tibial condyle (Gerdy's tubercle)
• Function: Stabilizes the knee in extension and the hip by holding the femoral head in the acetabulum

Clinical: IT Band Syndrome - overuse injury in runners; lateral knee pain. Pain on Ober's test (passive hip adduction with knee flexed in side-lying).

Saphenous Opening (Fossa Ovalis)

• The one major aperture in the fascia lata
• Located on the anterior thigh, just below the medial end of the inguinal ligament
• Allows the great saphenous vein to pass from superficial to deep fascia to join the femoral vein
• The margin spirals (cribriform fascia covers it - perforated like a sieve)

Clinical: Femoral Hernia exits through the femoral canal, which lies just medial to the saphenous opening. A "lump below the inguinal ligament, medial to the femoral pulse" = femoral hernia until proven otherwise.

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3. LUMBOSACRAL PLEXUS, CUTANEOUS SUPPLY & DERMATOMES

Formation

Mnemonic for lumbosacral plexus roots: "2 from 2, 2 from 3, 2 from 4" - L2, L3, L4 each contribute to Femoral AND Obturator nerves Sciatic = "L4 down to S3" = remember "4,5 and S 1,2,3"

Key Dermatomes (Lower Limb)

Mnemonic for reflexes: "L3-4 = Knee jerk (Patella)" / "S1-2 = Ankle jerk (calcaneal tendon)"

Exam High-Yield: Test L4 = knee jerk + medial foot sensation. Test L5 = big toe dorsiflexion. Test S1 = ankle jerk + small toe sensation.

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4. MUSCLES OF ANTERIOR COMPARTMENT OF THIGH

Mnemonic for Quadriceps: "I Really Value Muscles" = Intermedius, Rectus, Vastus (M, L, I)

Sartorius: "The Tailor's Muscle"

• Longest muscle in the body
• Crosses the thigh obliquely from ASIS to pes anserinus
• Action: Sitting cross-legged position = flex+abduct+laterally rotate hip + flex knee
• Forms the lateral border of the femoral triangle

Pes Anserinus ("Goose's Foot"): The combined tendon of Sartorius + Gracilis + Semitendinosus at the medial tibia Mnemonic: "Say Grace before Tea" = Sartorius, Gracilis, Semitendinosus

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5. NERVES & VESSELS OF ANTERIOR COMPARTMENT OF THIGH

Femoral Nerve (L2, L3, L4)

• Largest branch of the lumbar plexus
• Runs in the groove between iliacus and psoas, enters thigh lateral to femoral artery, outside the femoral sheath
• Divides into anterior and posterior divisions just below the inguinal ligament
• Anterior division: motor to sartorius, sensory to medial/anterior thigh
• Posterior division: motor to quadriceps, sensory - gives the saphenous nerve (the only cutaneous nerve to reach the foot from the femoral)

Clinical: Femoral nerve injury → loss of knee extension (quadriceps), loss of knee jerk reflex, sensory loss medial leg/foot. Patient cannot climb stairs.

Femoral Artery

• Continuation of external iliac artery below the inguinal ligament
• Enters thigh via femoral triangle → passes into adductor canal → exits as popliteal artery through the adductor hiatus of adductor magnus
• Major branch: Deep femoral artery (profunda femoris) - arises ~3.5 cm below inguinal ligament; gives:
  • Medial femoral circumflex artery (MFCA) - supplies femoral head (at risk in neck of femur fractures)
  • Lateral femoral circumflex artery (LFCA)
  • 3-4 perforating arteries to posterior thigh

Clinical: Femoral Pulse palpated at midinguinal point (midpoint between ASIS and pubic symphysis). This is where you compress for CPR-related femoral procedures and for vascular access.

Femoral Vein

• Lies medial to femoral artery in femoral triangle
• Receives great saphenous vein at saphenous opening
• Becomes external iliac vein above inguinal ligament

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6. HIP JOINT AND MOVEMENTS

Type & Articulation

• Multiaxial ball-and-socket synovial joint
• Ball: spherical head of femur (covered by hyaline cartilage except the fovea)
• Socket: lunate surface of acetabulum + deepened by the acetabular labrum (fibrocartilage)
• Transverse acetabular ligament converts the acetabular notch into a foramen

Ligaments of the Hip (Extracapsular)

Mnemonic: "I Prevent Hyperextension, You Prevent Abduction, Is that clear?" = Ilio-Pubo-Ischio

Movements of the Hip Joint

Blood Supply to Femoral Head

• Main supply: Retinacular (capsular) vessels from MFCA → ascend along femoral neck
• Minor: Ligamentum teres artery (obturator artery branch)
• Clinical: Avascular necrosis (AVN) of femoral head occurs with intracapsular neck of femur fractures (disrupts retinacular vessels), dislocations, and corticosteroid use.

High-Yield Exam: Trochanteric fractures (extracapsular) do NOT disrupt blood supply → rarely cause AVN. Subcapital fractures (intracapsular) → HIGH risk of AVN.

Trendelenburg Sign (High-Yield)

• Tests gluteus medius/minimus (superior gluteal nerve L4, L5, S1)
• When standing on the affected leg, the contralateral pelvis DROPS (positive Trendelenburg)
• Causes: Gluteus medius weakness, superior gluteal nerve palsy, hip dislocation, coxa vara

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7. FEMORAL SHEATH, FEMORAL RING, FEMORAL CANAL + FEMORAL TRIANGLE & ADDUCTOR CANAL

Femoral Sheath

• A funnel-shaped sleeve of fascia surrounding the femoral vessels
• Continuous with: transversalis fascia (anteriorly) and iliac fascia (posteriorly) from the abdomen
• Contains 3 compartments (lateral to medial):
  1. Lateral - Femoral Artery
  2. Middle - Femoral Vein
  3. Medial - Femoral Canal (lymphatics)

Mnemonic: "NAVeL" reading from lateral to medial under inguinal ligament: Nerve - Artery - Vein - Lymphatics (empty space = femoral canal) Note: Nerve is OUTSIDE the sheath; Artery, Vein, Lymphatics are inside.

Femoral Canal

• The most medial compartment of the femoral sheath
• Contains: lymph nodes (including Cloquet's node) + loose areolar tissue
• Its superior opening = Femoral Ring (boundaries: inguinal ligament anteriorly, femoral vein laterally, lacunar ligament medially, pectineal ligament posteriorly)
• Function: Allows femoral vein to expand during increased venous return

Clinical: Femoral Hernia - abdominal contents herniate through the femoral ring into the femoral canal. More common in WOMEN (wider pelvis → wider femoral ring). Presents below and lateral to the pubic tubercle (below inguinal ligament). High risk of strangulation because the femoral ring margins are rigid.

Distinguish from Inguinal hernia: Inguinal hernia = ABOVE and medial to pubic tubercle. Femoral hernia = BELOW and lateral to pubic tubercle.

Femoral Triangle

• Base (top): Inguinal ligament
• Lateral border: Medial border of sartorius
• Medial border: Medial border of adductor longus
• Floor: Iliopsoas (laterally) + Pectineus + Adductor longus (medially)
• Roof: Fascia lata + cribriform fascia at saphenous opening

Mnemonic: "SiAL" - Sartorius (lateral), Adductor longus (medial), Inguinal ligament (base)

• Femoral nerve (+ branches)
• Femoral artery (+ branches)
• Femoral vein (receives great saphenous)
• Deep inguinal lymph nodes

Adductor Canal (Hunter's Canal / Subsartorial Canal)

• A fascial tunnel in the middle third of the medial thigh
• Begins at the apex of the femoral triangle, ends at the adductor hiatus of adductor magnus
• Boundaries:
  • Anteromedial roof: Sartorius muscle
  • Lateral wall: Vastus medialis
  • Posterior wall: Adductor longus (above) and adductor magnus (below)
• Contents: Femoral artery, Femoral vein, Saphenous nerve, Nerve to vastus medialis

Clinical: Adductor canal block (ultrasound-guided) is used for postoperative analgesia after total knee replacement - it blocks the saphenous nerve without affecting quadriceps strength.

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8. GLUTEAL REGION

Muscles (Superficial to Deep)

1. Gluteus Maximus - largest muscle; origin: ilium/sacrum/coccyx; insert: IT band (upper 3/4) + gluteal tuberosity (lower 1/4); action: extend + laterally rotate hip; nerve: inferior gluteal nerve (L5, S1, S2)
2. Gluteus Medius - fan-shaped; covers gluteus minimus; abducts and medially rotates; nerve: superior gluteal nerve (L4, L5, S1)
3. Tensor Fasciae Latae (TFL) - most anterior; inserts into IT band; nerve: superior gluteal nerve
4. Gluteus Minimus - deepest of superficial group; abducts + medially rotates; nerve: superior gluteal nerve

1. Piriformis (exits above it: superior gluteal nerve/vessels; exits below: all other structures)
2. Obturator Internus (+ Gemellus Superior + Gemellus Inferior)
3. Quadratus Femoris (most inferior)
4. Obturator Externus (deep to all, in the medial compartment actually)

Mnemonic for Deep 6: "P-GO-GQ" = Piriformis, Gemellus Superior, Obturator Internus, Gemellus Inferior, Quadratus Femoris (like a magazine - "P.G.O.G.Q") Or: "Pretty Girls Often Get Quilted" = Piriformis, Gemellus sup, Obturator int, Gemellus inf, Quadratus femoris

Structures Through Greater Sciatic Foramen

• Superior gluteal nerve and vessels

• Pudendal nerve
• Obturator internus nerve
• Posterior cutaneous nerve of thigh
• Inferior gluteal nerve and vessels
• Sciatic nerve
• Also: Nerve to quadratus femoris + its artery

Mnemonic: "2 Pigs On Stools in the ISF" = 2P (Pudendal, Post cut nerve), O (Obturator int n), S (Sciatic), and the Inferior gluteal stuff

Piriformis Rule (High-Yield)

Clinical: Piriformis Syndrome - piriformis muscle compresses sciatic nerve, causing buttock pain + sciatica-like symptoms without disc pathology. Pain worse with sitting, hip external rotation stretches it.

Gluteal Injection Safe Zone

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9. MEDIAL COMPARTMENT OF THIGH

Mnemonic: "GALBPO" = Gracilis, Adductor Longus, Adductor Brevis, Pectineus, Obturator Externus, (Adductor Magnus)

Obturator Nerve (L2, L3, L4)

• Passes through the obturator canal into the medial thigh
• Divides into anterior and posterior divisions at the level of obturator externus
• Anterior division: superficial to adductor brevis; supplies adductors longus, brevis, gracilis, pectineus (sometimes)
• Posterior division: deep to adductor brevis; supplies obturator externus and adductor magnus (adductor part)

Clinical: Obturator nerve injury - difficulty adducting thigh; sensory loss medial thigh. Can occur with pelvic fractures or obstetric trauma. The obturator nerve also carries referred pain from the hip to the medial knee - "hip disease presenting as knee pain."

Adductor Magnus - The "2-in-1" Muscle

• Adductor part: obturator nerve, adducts
• Hamstring (ischial) part: tibial nerve, extends hip - behaves like a hamstring
• Has the adductor hiatus through which femoral vessels pass to become popliteal vessels

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10. SUPERFICIAL VEINS OF LOWER LIMB: GREAT & SMALL SAPHENOUS VEINS + LYMPHATICS

Great Saphenous Vein (GSV)

• Longest vein in the body
• Formed by union of: dorsal venous arch + dorsal vein of the great toe, on the medial side of the foot
• Course: Anterior to medial malleolus → up the medial leg → posterior to medial condyle of femur → through the saphenous opening → drains into femoral vein
• Has ~10-12 valves
• Receives tributaries: superficial epigastric vein, superficial circumflex iliac vein, superficial external pudendal vein (the "EPP" tributaries) near the saphenofemoral junction

Mnemonic for GSV tributaries at SFJ: "I See Pretty Elephants" = Inferior (superficial) Epigastric, Superficial Circumflex Iliac, Superficial External Pudendal

Clinical: Varicose Veins - most commonly from incompetent valves at the saphenofemoral junction. The long tortuous dilated veins are the GSV tributaries. Test with Trendelenburg test (occlude at saphenous opening, release = rapid filling = valvular incompetence). Treated with thermal ablation or stripping.

Clinical: GSV for bypass surgery - the GSV is commonly harvested for coronary artery bypass grafts (CABG) and peripheral arterial bypass surgery.

Small Saphenous Vein (SSV)

• Formed on the lateral side of the foot (dorsal venous arch + dorsal vein of little toe)
• Runs posterior to lateral malleolus → up the back of the calf → pierces deep fascia in popliteal fossa → drains into popliteal vein
• Accompanied by sural nerve in the calf

High-Yield: GSV = medial, ankle to groin (femoral vein). SSV = lateral/posterior, ankle to popliteal fossa (popliteal vein).

Perforating (Communicating) Veins

• Connect superficial to deep venous systems
• Valves normally direct blood from superficial to deep
• When valves fail → varicose veins and venous hypertension

Lymphatic Drainage

• Parallel the inguinal ligament in the superficial fascia
• Extend inferiorly along the terminal GSV
• Drain: gluteal region, lower abdominal wall, perineum, superficial lower limb
• Efferents: → external iliac nodes

• Medial to femoral vein in femoral canal
• Most superior = Cloquet's (Rosenmüller's) node (at femoral ring)
• Drain: deep lymphatics along femoral vessels + glans penis/clitoris
• Efferents: → external iliac nodes via femoral canal

• Behind the knee, near popliteal vessels
• Drain: posterior leg + foot (along SSV), and deep leg structures
• Efferents: → inguinal nodes

Clinical: Sentinel node in melanoma - a melanoma on the lateral lower limb/foot may drain to popliteal nodes first. Medial limb + whole limb drains to superficial inguinal nodes. The genitalia (penis/scrotum/labia/perineum) drain to superficial inguinal nodes - important for STI lymphadenopathy.

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11. POSTERIOR COMPARTMENT OF THIGH (HAMSTRINGS)

The 3 Hamstring Muscles

Mnemonic: "BEST" = Biceps, sEmitendinosus, Semimembranosus, all Tibial division except short head of biceps (fibular/peroneal division)

Key Point: Biceps femoris = laterally rotates the leg at the knee. Semimembranosus/semitendinosus = medially rotate the leg.

Hamstring Clinical Anatomy

Clinical: Hamstring Strain - most common at the musculotendinous junction near the ischial tuberosity. Sprinting athletes. The long head of biceps femoris is most commonly injured.

Clinical: Referred pain - the posterior cutaneous nerve of the thigh (S1-S3) covers the back of the thigh; hamstring pain can mimic sciatica.

Neurovascular Supply (Posterior Thigh)

• Nerve: Sciatic nerve (L4-S3) - runs midline, between hamstrings on medial side and short head of biceps on lateral side
• Artery: Perforating branches of profunda femoris (3-4 perforators pierce the adductor magnus)
• Sciatic nerve divides into tibial + common fibular nerve proximal to the popliteal fossa (or in it)

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12. KNEE JOINT

Type & Articulation

• Largest synovial joint in the body
• Two components:
  1. Femorotibial (weight-bearing hinge)
  2. Femoropatellar (patella glides on femur, redirects quadriceps force)
• Basically a hinge joint (flexion/extension) with some rotation

Menisci (High-Yield)

• Two fibrocartilaginous semilunar discs between femur and tibia
• Medial meniscus - C-shaped, larger, firmly attached to medial capsule and tibial collateral ligament → less mobile → more commonly torn
• Lateral meniscus - O-shaped (more circular), less firmly attached → more mobile

Clinical: Meniscal Tears - medial more common. O'Brien's sign (McMurray test): flex knee fully, rotate tibia medially, extend = medial meniscus click/pain. Medial meniscus tears often accompany ACL injuries.

Cruciate Ligaments

Mnemonic: "ACL prevents Anterior tibial displacement" = ACL = Anterior drawer positive if torn PCL = Posterior drawer positive if torn. PCL is stronger (twice the size of ACL).

Collateral Ligaments

• Tibial (medial) collateral ligament - attached to the medial capsule and medial meniscus → blows to the lateral side of knee damage it (valgus force)
• Fibular (lateral) collateral ligament - cord-like, NOT attached to lateral meniscus → blows to the medial side of knee (varus force)

"Unhappy Triad" (O'Donoghue's Triad)

• Valgus force injury to the knee: ACL + Medial collateral ligament + Medial meniscus
• Classic "tackle from the side" injury in football

Locking Mechanism of the Knee

• When fully extended, the knee "screws home" = femur medially rotates on tibia (or tibia laterally rotates on femur)
• Popliteus muscle "unlocks" the knee by laterally rotating the femur to initiate flexion
• Popliteus = "key to the knee joint"

Clinical Tests (Exam High-Yield)

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13. ANTERIOR COMPARTMENT OF LEG

Muscles

Mnemonic: "The Happy Dog Exerts Force" = Tibialis anterior, (H)allucis longus, Digitorum longus, (E)xtensor retinaculum, Fibularis tertius - all deep fibular nerve, all dorsiflex

Nerve & Vessels of Anterior Compartment

• Deep fibular (peroneal) nerve - branch of common fibular nerve; runs with anterior tibial vessels; ends on dorsum of foot supplying skin in 1st web space between toes 1 and 2
• Anterior tibial artery - branch of popliteal; passes through the interosseous membrane; continues as dorsal pedis artery at the foot; palpated at dorsum of foot between tendons of EHL and EDL

Clinical: Anterior Compartment Syndrome - most common compartment syndrome in the leg. Swelling after fracture or excessive exercise → increased pressure in rigid compartment → ischemia. Signs: severe pain (especially on passive stretch of muscles), tight compartment, weak dorsiflexion, loss of sensation in 1st web space. Emergency fasciotomy required.

Clinical: Foot Drop - deep fibular nerve injury (usually at fibular neck where the common fibular nerve winds around) → loss of dorsiflexion and toe extension → foot drop (foot slaps during walking, high stepping gait). L4-L5 nerve root lesion can give the same picture.

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14. LATERAL COMPARTMENT OF LEG & DORSUM OF FOOT

Muscles (Lateral Compartment)

High-Yield: Both evert the foot. Fibularis Longus tendon passes under the foot diagonally to reach the MEDIAL side - supporting the transverse arch.

Clinical: Peroneal nerve injury (common fibular nerve) at the fibular neck:

• Loss of dorsiflexion (deep fibular nerve component) = foot drop
• Loss of eversion (superficial fibular nerve component)
• Sensory loss dorsum of foot + lateral leg
• Causes: fibular neck fracture, plaster cast pressure, prolonged squatting, crossed-leg sitting

Dorsum of Foot

• Extensor Digitorum Brevis + Extensor Hallucis Brevis - short extensors; only muscles on dorsum of foot; supplied by deep fibular nerve
• Dorsal pedis artery - continuation of anterior tibial; palpated lateral to EHL tendon; gives arcuate artery and deep plantar artery to foot
• Retinaculum system: Superior and inferior extensor retinacula hold the tendons to the dorsum

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15. POSTERIOR COMPARTMENT OF LEG

Superficial Group (Triceps Surae)

Gastrocnemius + Soleus + Plantaris → all insert via calcaneal (Achilles) tendon onto calcaneus

Clinical: Achilles Tendon Rupture - "felt like being kicked in the back of the leg." Positive Thompson test (squeeze calf = no plantarflexion). Gap palpable. Most common in middle-aged recreational athletes ("weekend warriors"). Treatment: surgical repair or immobilization.

Deep Group

Mnemonic for deep posterior leg muscles: "Tom, Dick, ANd Harry" = Tibialis posterior, flexor Digitorum longus, (posterior tibial) Artery/Nerve, flexor Hallucis longus (order of structures from medial to lateral behind the medial malleolus)

Posterior Tibial Vessels and Tibial Nerve

• Posterior tibial artery: main artery of posterior compartment; terminates behind medial malleolus by dividing into medial and lateral plantar arteries. Palpated posterior to medial malleolus (between the medial malleolus and the Achilles tendon).
• Tibial nerve: runs with posterior tibial artery; passes through the tarsal tunnel behind the medial malleolus → divides into medial and lateral plantar nerves

Clinical: Tarsal Tunnel Syndrome - compression of tibial nerve in the tarsal tunnel (flexor retinaculum behind medial malleolus). Symptoms: burning pain and paresthesia on the sole of the foot, worse at night. Analogous to carpal tunnel syndrome in the wrist.

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16. POPLITEAL FOSSA

Shape & Boundaries

• Diamond-shaped space posterior to the knee

Contents (from Superficial to Deep, Lateral to Medial)

1. Common fibular nerve (most lateral, most superficial)
2. Tibial nerve (central, descends vertically)
3. Popliteal vein (middle)
4. Popliteal artery (deepest, closest to bone)

Mnemonic for depth: "VAN" rule at popliteal fossa, reversed = "NAV" from anterior to posterior: Nerve (tibial) is most posterior = most superficial, Artery is deepest against bone, Vein between them. Remember: "Popliteal artery is the DEEPEST structure in the popliteal fossa" (deepest against the bone → most vulnerable in supracondylar fractures of femur)

Clinical: Popliteal aneurysm - most common peripheral arterial aneurysm. Can compress structures. Also: Baker's cyst = fluid-filled swelling in popliteal fossa (communication with knee joint; seminmembranosus bursa). Palpated as a soft lump in the popliteal fossa.

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17. FOOT: FASCIA AND MUSCLES

Plantar Aponeurosis (Plantar Fascia)

• Thick fibrous band from calcaneal tuberosity to the bases of the proximal phalanges
• Supports the medial longitudinal arch
• Clinical: Plantar Fasciitis - most common cause of heel pain. Pain on first steps in the morning ("post-static dyskinesia"). Tenderness at the calcaneal insertion. Treated with stretching, orthotics, NSAIDs.

Muscles of the Sole (4 Layers)

Mnemonic: "Abby Flexed, Donald Abducted, All Queued, Lovely Feeling, Hairy Adductors, Fingernails Do, PAD/DAB" Simpler: Layer 1 = Abductors and short flexors. Layer 2 = Quads + Lumbricals. Layer 3 = Hallux + 5th toe muscles. Layer 4 = Interossei.

Dorsal Interossei = DAB (Dorsals ABduct) / Plantar Interossei = PAD (Plantars ADduct)

Flexor Retinaculum (Laciniate Ligament)

• Bridges medial malleolus to calcaneus
• Forms the tarsal tunnel
• Contains (medial to lateral via "Tom, Dick, ANd Harry" = see section 15)

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18. NEUROVASCULAR SUPPLY OF FOOT

Arteries

Plantar arch is analogous to the palmar arch in the hand

Nerves of the Foot

High-Yield: The sole is supplied by the tibial nerve (via medial and lateral plantar nerves). The dorsum is supplied by the fibular nerves.

Medial plantar nerve = "the median nerve of the foot" (supplies the medial 3.5 toes, like the median nerve supplies the lateral 3.5 fingers in the hand)

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19. ARCHES OF THE FOOT

Why Do Arches Exist?

• Absorb and distribute downward forces during standing and walking
• Allow adaptation to uneven surfaces
• Spring-like energy storage and release

Types of Arches

• Medial longitudinal arch (MLA) - Calcaneus → Talus → Navicular → Cuneiforms → Metatarsals 1-3. Highest arch. Supported by: spring ligament (plantar calcaneonavicular), tibialis posterior, FHL.
• Lateral longitudinal arch (LLA) - Calcaneus → Cuboid → Metatarsals 4-5. Low arch, nearly flat.

• At the level of the mid-foot (metatarsal bases + cuboid + cuneiforms)
• Supported by: fibularis longus tendon (winds under foot), deep transverse metatarsal ligaments, adductor hallucis

Support Mechanisms

1. Bony architecture (keystone = talus for MLA, cuboid for lateral)
2. Ligaments (passive): Spring ligament (most important for MLA), long plantar ligament, short plantar ligament, plantar aponeurosis
3. Muscles (active): Tibialis posterior (MLA), fibularis longus (transverse arch + lateral arch), intrinsic foot muscles, FHL

Clinical: Flat Foot (Pes Planus) - loss of medial longitudinal arch. Most common is acquired (tibialis posterior tendon dysfunction in adults). Presents with medial ankle pain and progressive flat foot deformity. Test: single-leg heel rise test - inability to rise onto toes.

Clinical: High Arch (Pes Cavus) - excessively high medial longitudinal arch. Associated with neuromuscular disorders (Charcot-Marie-Tooth, Friedreich's ataxia). Leads to increased metatarsal head pressures + claw toes.

High-Yield: The medial longitudinal arch is the clinically most important. It is supported primarily by the spring (plantar calcaneonavicular) ligament passively and tibialis posterior actively.

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20. NERVE INJURIES OF THE LOWER LIMB

Key Clinical Scenarios

HIGH-YIELD INJECTION SAFETY:

• Gluteal injection: Upper OUTER (superolateral) quadrant = safe from sciatic nerve
• Femoral nerve block: Lateral to the femoral artery (nerve is outside the femoral sheath)
• Knee aspiration: Superolateral patella approach most common

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QUICK MNEMONICS REVISION TABLE

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DISTINCTION-LEVEL EXAM HIGH-YIELD POINTS

1. Femoral hernia is below + lateral to pubic tubercle; inguinal hernia is above + medial - this distinction is frequently tested
2. Popliteal artery is the DEEPEST structure in the popliteal fossa - injured in supracondylar fractures
3. Medial meniscus is more commonly torn than lateral because it is firmly anchored to the tibial collateral ligament
4. The ACL prevents anterior tibial displacement (Lachman test > anterior drawer test in sensitivity)
5. Tibialis posterior is the key dynamic supporter of the medial longitudinal arch - its failure = acquired flat foot
6. Superior gluteal nerve injury = Trendelenburg sign; inferior gluteal nerve injury = no Trendelenburg but cannot extend hip (rise from chair)
7. The sciatic nerve exits below piriformis (in most people); in some, the common fibular component passes THROUGH piriformis → variant causing piriformis syndrome
8. Common fibular nerve is the most commonly injured nerve in the lower limb because it winds around the fibular neck subcutaneously
9. Medial femoral circumflex artery is the main blood supply to the femoral head via retinacular vessels → its disruption in intracapsular neck of femur fractures causes AVN
10. The femoral nerve is OUTSIDE the femoral sheath (lateral to it) - not enclosed within it
11. Obturator nerve injury causes referred knee pain - always examine the hip in a patient with unexplained knee pain
12. Great saphenous vein is always anterior to medial malleolus; small saphenous vein is posterior to lateral malleolus - used in venous cutdown procedures
13. Quadriceps (especially VMO = vastus medialis oblique) stabilizes the patella - VMO weakness → patellofemoral syndrome
14. Sartorius is the longest muscle; Gluteus maximus is the largest muscle; Soleus is the most powerful plantarflexor
15. Adductor magnus has a "dual personality" - adductor part (obturator nerve) and hamstring part (tibial division of sciatic); has the adductor hiatus through which the femoral artery becomes the popliteal artery

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