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COMPREHENSIVE ANATOMY NOTES

Upper Limb · Lower Limb · Spine

(Snell · BD Chaurasia · Moore/KLM)

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PART 1: SPINE (VERTEBRAL COLUMN)

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1.1 Overview of the Vertebral Column

• Primary (kyphotic): Thoracic, sacrococcygeal — present from fetal life
• Secondary (lordotic): Cervical (develops with head lifting), Lumbar (develops with walking)
• Clinical: Scoliosis (lateral), Kyphosis (exaggerated thoracic), Lordosis (exaggerated lumbar)

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1.2 A Typical Vertebra (BD/Snell/KLM)

1. Vertebral body — weight-bearing; upper and lower surfaces covered by hyaline cartilage
2. Vertebral arch — composed of two pedicles + two laminae
3. Processes: 1 spinous, 2 transverse, 4 articular (2 superior, 2 inferior)
4. Vertebral foramen — spinal cord passes through; all together form the vertebral canal

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1.3 Regional Vertebral Features (Snell emphasis)

Cervical (C3–C6 typical):

• Small body, bifid spine, foramen transversarium (vertebral artery C1–C6; vertebral vein C1–C7)
• Uncinate process (of Luschka) on lateral body margins
• C1 (Atlas): No body, no spinous process; ring-shaped; superior facets for occipital condyles; transverse ligament holds dens
• C2 (Axis): Dens (odontoid process) = embryological body of C1 fused to C2; pivot for rotation
• C7 (Vertebra prominens): Longest non-bifid spinous process, easily palpable; foramen transversarium for vertebral vein only (not artery)

Thoracic:

• Costal (demi)facets on body — superior + inferior — for rib head articulation (except T1 full facet above, demi below; T10 full facet; T11, T12 single full facet on pedicle)
• Costal facet on transverse process for rib tubercle (absent T11, T12)
• Long spinous processes overlap each other — "roof-tile" arrangement
• Vertebral foramen is circular and small

Lumbar:

• Largest vertebral body
• Short, quadrilateral spinous process
• Accessory and mamillary processes on transverse and articular processes
• Spinal cord ends at L1–L2 (conus medullaris); below this = cauda equina
• L3–L4 / L4–L5 most common disc herniation sites

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1.4 Intervertebral Discs (KLM/BD/Snell)

• Nucleus pulposus — central gelatinous core; remnant of notochord; ~80% water; resists compression
• Anulus fibrosus — concentric lamellae of fibrocartilage surrounding nucleus
• Vertebral end plates — hyaline cartilage; nutrition via diffusion

• Disc herniation (prolapse): nucleus pulposus herniates posterolaterally → compresses nerve root in intervertebral foramen
• Most common: L4–L5 (L5 root) and L5–S1 (S1 root)
• Central herniation → compresses cauda equina → bilateral leg pain, bladder/bowel dysfunction

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1.5 Ligaments of the Vertebral Column (BD Chaurasia)

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1.6 Joints of the Vertebral Column

1. Joints of the bodies — secondary cartilaginous (symphysis); via intervertebral discs
2. Joints of the arches (zygapophyseal / facet joints) — synovial plane joints; orientation varies by region:
   • Cervical: near horizontal → allows flexion/extension + rotation
   • Thoracic: near vertical frontal plane → allows rotation, limits flexion
   • Lumbar: sagittal plane → allows flexion/extension, restricts rotation
3. Atlanto-occipital joint — synovial condyloid; flexion/extension ("yes" movement); C1 on skull
4. Atlanto-axial joint — median (pivot) + lateral; rotation ("no" movement); C1 on C2
   • Secured by: transverse ligament of atlas, alar ligaments, apical ligament, tectorial membrane

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1.7 Spinal Cord & Meninges (Snell Clinical Anatomy)

• Meninges (outside→in): Dura mater → arachnoid mater → pia mater
• Spaces: Epidural (fat + venous plexus), Subdural (potential), Subarachnoid (CSF)
• Spinal cord ends at L1/L2 in adults (L3 in neonates)
• Conus medullaris → filum terminale (pia) → attaches to coccyx
• Cauda equina = nerve roots L2–Co below conus, hanging in CSF
• Lumbar puncture: L3/L4 or L4/L5 interspace; safe below L2

• C4 — shoulder top
• C6 — thumb
• C7 — middle finger
• C8 — little finger
• T4 — nipple level
• T10 — umbilicus
• L1 — inguinal region
• L4 — medial leg/great toe
• L5 — dorsum of foot/2nd toe
• S1 — little toe/sole

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1.8 Back Muscles (BD Chaurasia / Snell)

Superficial (extrinsic — limb movers):

• Trapezius — spinal accessory nerve (CN XI) + C3,C4 (sensory); upper/middle/lower fibers
• Latissimus dorsi — thoracodorsal nerve (C6,7,8)
• Rhomboids (major + minor) — dorsal scapular nerve (C5)
• Levator scapulae — dorsal scapular nerve (C3,4,5)
• Serratus posterior (superior + inferior) — intercostal nerves

Deep (intrinsic — true back muscles):

1. Superficial layer: Splenius capitis, splenius cervicis
2. Intermediate layer (Erector spinae = sacrospinalis):
   • Iliocostalis (lateral column) — rib angles
   • Longissimus (middle column) — transverse processes
   • Spinalis (medial column) — spinous processes
3. Deep layer (Transversospinalis group):
   • Semispinalis, Multifidus, Rotatores
   • Multifidus — most important stabilizer; attaches 2–4 vertebrae apart
4. Suboccipital muscles (C1 dorsal ramus):
   • Rectus capitis posterior major/minor, Obliquus capitis superior/inferior
   • Form suboccipital triangle — vertebral artery + C1 dorsal ramus pass here

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PART 2: UPPER LIMB

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2.1 Overview & Regions

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2.2 Bones of the Upper Limb

Clavicle (BD/Snell):

• S-shaped; only bony link between upper limb and axial skeleton
• Medial 2/3 — convex anteriorly; Lateral 1/3 — concave anteriorly
• Common fracture site: junction of middle/lateral thirds
• No medullary cavity (membranous ossification); first bone to ossify (5th–6th week fetal)

Scapula:

• Spine, acromion, coracoid process, glenoid cavity, supraspinous/infraspinous/subscapular fossae
• Anatomical neck — narrow neck around glenoid
• Coracoid process — attachment of pectoralis minor, coracobrachialis, short head biceps
• Winging of scapula — serratus anterior weakness (long thoracic nerve, C5,6,7 palsy)

Humerus:

• Head, anatomical neck, surgical neck, greater/lesser tubercles, intertubercular groove
• Surgical neck fracture → axillary nerve + posterior circumflex humeral artery injury
• Shaft fracture (midshaft) → radial nerve injury in spiral groove → wrist drop
• Medial and lateral epicondyles; medial epicondyle fracture → ulnar nerve injury
• Lateral epicondyle — extensor origin; Medial epicondyle — flexor origin
• Capitulum (articulates with radius head); Trochlea (articulates with ulna)

Radius & Ulna:

• Colles' fracture — distal radius fracture; dinner fork deformity; FOOSH (fall on outstretched hand)
• Smith's fracture — reversed Colles'; volar displacement
• Monteggia fracture — proximal ulna fracture + radial head dislocation
• Galeazzi fracture — distal radius fracture + distal radioulnar joint dislocation
• Olecranon fracture → triceps pull; Radial head fracture → common in adults

Hand Bones:

• 8 carpals (lateral→medial, proximal row: Scaphoid, Lunate, Triquetrum, Pisiform; distal row: Trapezium, Trapezoid, Capitate, Hamate)
• Mnemonic: She Looks Too Pretty, Try To Catch Her
• Scaphoid fracture — most common carpal fracture; FOOSH; avascular necrosis risk (proximal pole); snuffbox tenderness
• 5 metacarpals + 14 phalanges (thumb = 2, others = 3)

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2.3 Shoulder Region

Glenohumeral Joint (Snell/KLM):

• Type: Synovial, ball-and-socket, multiaxial
• Articular surfaces: Head of humerus (1/3 sphere) + glenoid cavity (1/4 sphere) of scapula + glenoid labrum (fibrocartilage deepens socket)
• Capsule: Lax inferiorly; reinforced by glenohumeral ligaments (superior, middle, inferior)
• Movements: Flexion/extension, abduction/adduction, medial/lateral rotation, circumduction
• Most mobile joint — most commonly dislocated joint
• Most common dislocation: anterior (subcoracoid) — arm in abduction + external rotation

• Rotator cuff holds humeral head in glenoid fossa during movements
• Supraspinatus most commonly torn; presents with painful arc (60–120°)

Shoulder Abduction — Mechanism (Snell):

• 0–15°: Supraspinatus initiates
• 15–90°: Deltoid (axillary nerve C5,6)
• 90–150°: Scapular rotation (serratus anterior + trapezius)
• Above 90°: Lateral rotation of humerus needed to clear the greater tubercle from under acromion

Subacromial (Subdeltoid) Bursa:

• Between rotator cuff and coracoacromial arch
• Inflamed in subacromial impingement syndrome
• Does NOT communicate with glenohumeral joint (normally)

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2.4 Axilla (BD Chaurasia)

• Apex: Axillary inlet (clavicle, scapular margin, rib I)
• Base: Axillary fascia + skin
• Anterior wall: Pectoralis major, pectoralis minor, subclavius, clavipectoral fascia
• Posterior wall: Subscapularis, teres major, latissimus dorsi
• Medial wall: Serratus anterior on ribs 1–4
• Lateral wall: Intertubercular groove of humerus (narrowest)

• Part 1 (medial to pec minor): Superior thoracic artery
• Part 2 (behind pec minor): Thoracoacromial + Lateral thoracic
• Part 3 (lateral to pec minor): Anterior circumflex humeral + Posterior circumflex humeral + Subscapular (→ circumflex scapular + thoracodorsal)

1. Anterior (pectoral) — along lateral thoracic vessels; drain breast
2. Posterior (subscapular) — along subscapular vessels
3. Lateral — along axillary vein; drain upper limb
4. Central — central fat pad
5. Apical — at apex; drain all others → subclavian lymph trunk

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2.5 Brachial Plexus (Snell — most tested topic)

• Roots → Trunks → Divisions → Cords → Branches
• Roots: C5, C6, C7, C8, T1
• Trunks: Upper (C5,6), Middle (C7), Lower (C8,T1)
• Divisions: Each trunk divides into anterior + posterior
• Cords: Lateral (C5,6,7 ant.), Posterior (all post.), Medial (C8,T1 ant.)
• Cords named relative to axillary artery

• Musculocutaneous nerve (C5,6,7)
• Lateral root of median nerve

• Ulnar nerve (C8,T1)
• Medial root of median nerve
• Medial cutaneous nerve of arm (C8,T1)
• Medial cutaneous nerve of forearm (C8,T1)

• Axillary nerve (C5,6)
• Radial nerve (C5,6,7,8,T1)
• Upper subscapular (C5,6)
• Lower subscapular (C5,6)
• Thoracodorsal (C6,7,8)

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2.6 Individual Nerve Palsies (Snell — Clinical Anatomy)

Axillary Nerve (C5,C6):

• Damaged by: Surgical neck humerus fracture, anterior shoulder dislocation
• Motor loss: Deltoid (abduction 15–90°), Teres minor
• Sensory loss: Regimental badge area (lower deltoid region)

Radial Nerve (C5–T1):

• Posterior cord → Spiral groove of humerus
• Damaged by: Midshaft humerus fracture ("Holstein-Lewis"), prolonged axillary pressure ("crutch palsy"), "Saturday night palsy" (arm over chair back)
• Motor loss: All extensors of elbow, wrist, fingers → Wrist drop
• Sensory loss: Dorsum of hand (1st web space most autonomously)
• High radial palsy (axilla): Also loses triceps (elbow extension)
• Posterior interosseous nerve (PIN) branch: Motor only → finger extension loss without wrist drop

Musculocutaneous Nerve (C5,6,7):

• Pierces coracobrachialis → innervates coracobrachialis, biceps brachii, brachialis
• Continues as lateral cutaneous nerve of forearm
• Rarely injured; isolated injury → weak elbow flexion + supination

Ulnar Nerve (C8,T1):

• Medial cord → Medial epicondyle (cubital tunnel) → Guyon's canal (wrist)
• Damaged by: Medial epicondyle fracture, cubital tunnel syndrome, Guyon's canal
• Motor loss:
  • All interossei (palmar + dorsal)
  • 3rd + 4th lumbricals (ring + little finger)
  • Hypothenar muscles (abductor/flexor/opponens digiti minimi)
  • Adductor pollicis
  • Flexor carpi ulnaris + medial half flexor digitorum profundus
• Claw hand (ulnar): 4th and 5th fingers clawed; hyperextension at MCP, flexion at PIP/DIP ("benediction hand in partial")
• Wrist ulnar palsy — worse claw (intrinsics paralyzed but long flexors intact)
• Elbow ulnar palsy — less claw (FDP also paralyzed)
• Froment's sign: Compensatory IP flexion (flexor pollicis longus via AIN/median) when pinching paper due to adductor pollicis paralysis
• Sensory: Medial 1½ fingers, medial palm, little finger

Median Nerve (C5–T1):

• Lateral + medial roots → Flexor compartment forearm → Carpal tunnel
• Damaged by: Supracondylar fracture (in children — "high median"), carpal tunnel (low median)
• Motor loss (high — above elbow):
  • Pronators (pronator teres, pronator quadratus)
  • Most flexors of wrist/fingers (except FCU + medial FDP)
  • Thenar muscles (APB, OP, FPB superficial head)
  • Lateral 2 lumbricals
  • Ape hand deformity — thumb lies in plane of palm (no opposition)
  • Hand of benediction — when asked to flex, can't flex index and middle fingers
• Anterior interosseous nerve (AIN) — branch in forearm; supplies FPL, lateral FDP, pronator quadratus — "pinch test" (can't form O shape)
• Motor loss (low — at wrist/carpal tunnel):
  • Only thenar muscles (APB, OP, FPB) + lateral 2 lumbricals
  • Ape hand — thumb adducted + cannot oppose
• Sensory: Lateral 3½ fingers (palmar), nail beds of index/middle/lateral ring; carpal tunnel syndrome — pain/paraesthesia at night, Tinel's, Phalen's test

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2.7 Muscles of the Arm (BD Chaurasia)

Anterior Compartment (Flexors):

Posterior Compartment (Extensors):

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2.8 Cubital Fossa (Snell/KLM)

• Medial: Pronator teres
• Lateral: Brachioradialis
• Roof (floor of skin): Bicipital aponeurosis + superficial fascia
• Floor: Brachialis + supinator

• T — Tendon of biceps brachii
• A — Brachial Artery (divides here into radial + ulnar)
• N — Median Nerve
• (Radial nerve is just lateral to biceps tendon in floor)

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2.9 Forearm Muscles (BD Chaurasia)

Anterior Compartment (Pronators/Flexors) — Median nerve primarily:

• Pronator teres — median nerve; elbow flexion + pronation
• Flexor carpi radialis — median nerve; wrist flexion + abduction
• Palmaris longus — median nerve (absent in ~15%); tenses palmar aponeurosis
• Flexor carpi ulnaris — ulnar nerve; wrist flexion + adduction

• Flexor digitorum superficialis — median nerve; flexes PIP joints (digits 2–5)

• Flexor digitorum profundus — medial half ulnar nerve, lateral half AIN/median; flexes DIP joints
• Flexor pollicis longus — AIN (median nerve); flexes IP joint of thumb
• Pronator quadratus — AIN (median nerve); pure pronation

Posterior Compartment (Supinators/Extensors) — Radial nerve:

• Brachioradialis — elbow flexion (weakly); radial nerve
• Extensor carpi radialis longus/brevis — wrist extension + abduction
• Extensor digitorum communis — extends digits 2–5
• Extensor digiti minimi — extends little finger
• Extensor carpi ulnaris — wrist extension + adduction

• Supinator — supinates forearm (radial nerve → posterior interosseous nerve)
• Abductor pollicis longus, Extensor pollicis brevis, Extensor pollicis longus, Extensor indicis — all AIN/PIN

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2.10 Wrist and Hand (Snell/BD)

Carpal Tunnel:

• Boundaries: Flexor retinaculum (roof), carpal bones (floor + sides)
• Contents (9 tendons + 1 nerve): 4 tendons of FDS + 4 tendons of FDP + 1 FPL tendon + Median nerve
• Ulnar nerve and artery pass lateral to retinaculum in Guyon's canal

Palmar Fascia & Spaces:

• Palmar aponeurosis — triangular; extension of palmaris longus
• Thenar space (lateral): Between flexors and adductor pollicis
• Mid-palmar space (medial): Between flexors and metacarpals 3–5
• Dupuytren's contracture — fibrosis of palmar aponeurosis → ring + little finger flexion

Intrinsic Hand Muscles:

• Abductor pollicis brevis (APB) — most superficial; pure median nerve; abducts thumb
• Flexor pollicis brevis (FPB) — superficial head: median; deep head: ulnar
• Opponens pollicis (OP) — deepest; true opposition
• Adductor pollicis — ulnar nerve (not median); two heads (oblique + transverse)

• Abductor digiti minimi, Flexor digiti minimi brevis, Opponens digiti minimi

• 4 total; arise from FDP tendons
• 1st + 2nd (lateral): Median nerve
• 3rd + 4th (medial): Ulnar nerve
• Action: Flex MCP + Extend PIP/DIP (via extensor expansion)

• 4 Dorsal interossei — DAB (abduct digits from midline = 3rd digit)
• 3 Palmar interossei — PAD (adduct digits toward midline)

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2.11 Anatomical Snuff Box (Snell)

• Medial: Extensor pollicis longus
• Lateral: Extensor pollicis brevis + Abductor pollicis longus
• Floor: Scaphoid + trapezium

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2.12 Superficial Veins (KLM/Snell)

• Cephalic vein — lateral side, starts from dorsal venous arch, winds around lateral forearm → bicipital groove → deltopectoral groove → drains into axillary vein
• Basilic vein — medial side, pierces deep fascia at mid-arm → joins brachial vein → forms axillary vein
• Median cubital vein — connects cephalic to basilic at cubital fossa; used for venipuncture; separated from brachial artery by bicipital aponeurosis

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PART 3: LOWER LIMB

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3.1 Overview & Regions

1. Support body weight — center of gravity anterior to S2
2. Locomotion — integrated joint movements (hip, knee, ankle, subtalar)
3. Propulsion — plantarflexors (gastrocnemius, soleus) generate ~80% of propulsive force

• Inguinal ligament → femoral triangle (entry of femoral nerve, artery, vein, lymphatics)
• Popliteal fossa → between thigh and leg
• Tarsal tunnel (posteromedial ankle) → between leg and foot

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3.2 Bones of the Lower Limb

Pelvis:

• Os coxae = Ilium + Ischium + Pubis (fused at triradiate cartilage by age 15–16)
• ASIS, AIIS, PSIS, PIIS — key palpable landmarks
• Greater sciatic notch → greater sciatic foramen → piriformis exits + divides
• Lesser sciatic notch → lesser sciatic foramen
• Obturator foramen — largest foramen; closed by obturator membrane
• Male pelvis: Heart-shaped, narrow; Female pelvis: Oval/round, wider (obstetric conjugate >11 cm)

Femur:

• Head, neck, greater + lesser trochanters, intertrochanteric crest/line, linea aspera, medial/lateral condyles, medial/lateral epicondyles, patellar surface (trochlea)
• Neck-shaft angle: Normal ~126°; Coxa valga (>135°) — common in children; Coxa vara (<115°) — limb shortening
• Femoral neck fracture — blood supply from medial circumflex femoral artery; risk of avascular necrosis of femoral head
• Subcapital fracture — disrupts retinacular arteries → AVN

Tibia & Fibula:

• Tibia bears weight; fibula does not bear significant weight but anchors ankle mortise
• Tibial condyles, tibial tuberosity (patellar tendon insertion), gerdy's tubercle (ITB insertion)
• Pott's fracture — bimalleolar/trimalleolar ankle fracture
• Fibula head — common peroneal nerve winds around it → compression → foot drop

Patella:

• Largest sesamoid bone in body; within quadriceps tendon
• Blood supply: Genicular anastomosis
• Patella fracture — transverse (direct blow); avulsion (sudden quadriceps pull)

Foot Bones:

• 7 tarsals: Calcaneus, Talus, Navicular, Cuboid, Medial/Intermediate/Lateral Cuneiforms
• Mnemonic: Cubs Tend Not Coming Monday I Learn
• Calcaneus — largest tarsal; calcaneal tuberosity (heel); sustentaculum tali supports talus neck
• Talus — no muscle attachments; 3 articulations (tibia, fibula, calcaneus); prone to AVN
• 5 metatarsals + 14 phalanges

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3.3 Hip Joint (Snell/BD/KLM)

• Type: Synovial, ball-and-socket (most stable joint in body)
• Articular surfaces: Head of femur + acetabulum (deepened by acetabular labrum)
• Acetabulum: Formed by ilium (above), pubis (anteromedial), ischium (posteroinferior); articular surface = lunate surface; acetabular fossa = non-articular central portion with fat pad
• Ligaments:
  • Iliofemoral (Y-ligament of Bigelow) — strongest ligament in body; prevents hyperextension
  • Pubofemoral — inferior; limits abduction + extension
  • Ischiofemoral — posterior; limits medial rotation
  • Ligament of head of femur (ligamentum teres) — carries artery to femoral head (small contribution)
  • Transverse acetabular ligament — closes acetabular notch

• Medial circumflex femoral artery (main supply via retinacular arteries in capsule)
• Lateral circumflex femoral artery
• Artery in ligamentum teres (obturator artery) — minor, significant in children

• Most stable position: Extension, slight abduction + lateral rotation (packed position)

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3.4 Thigh Muscles (BD Chaurasia)

Anterior Compartment (Femoral nerve):

Medial Compartment (Adductors — Obturator nerve predominantly):

• Adductor longus — anterior, most prominent; obturator nerve
• Adductor brevis — obturator nerve
• Adductor magnus — two parts: adductor (obturator nerve) + hamstring (sciatic nerve/tibial); adductor hiatus
• Gracilis — most medial; obturator nerve; joins pes anserinus
• Pectineus — femoral nerve (and sometimes accessory obturator); adduction + flexion
• Obturator externus — obturator nerve; lateral rotation

Posterior Compartment (Hamstrings — Sciatic/Tibial nerve):

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3.5 Gluteal Region (Snell/BD)

Gluteal Muscles:

• Exits greater sciatic foramen; divides it into:
  • Above piriformis: Superior gluteal nerve + vessels
  • Below piriformis: Inferior gluteal nerve + vessels, Sciatic nerve, Posterior cutaneous nerve of thigh, Pudendal nerve + internal pudendal vessels, Nerve to obturator internus, Nerve to quadratus femoris

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3.6 Femoral Triangle (KLM/Snell)

• Base (superior): Inguinal ligament
• Medial: Adductor longus
• Lateral: Sartorius

• N — Femoral Nerve (most lateral; outside femoral sheath)
• A — Femoral Artery (in femoral sheath)
• V — Femoral Vein (in femoral sheath, medial to artery)
• Y — Lymphatics (Cloquet's node most medial)

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3.7 Knee Joint (Snell/BD/KLM)

• Type: Synovial, hinge (modified); largest joint in body
• Articular surfaces: Femoral condyles + tibial condyles + patella

• Medial meniscus — C-shaped; firmly attached to MCL → more often torn
• Lateral meniscus — O-shaped; more mobile → less often torn

• ACL (Anterior Cruciate Ligament): Femoral lateral condyle (posterior) → tibial intercondylar eminence (anterior); prevents anterior tibial displacement; pivot shift + Lachman test
• PCL (Posterior Cruciate Ligament): Femoral medial condyle (anterior) → posterior tibia; prevents posterior displacement; posterior sag + posterior drawer test
• MCL (Medial Collateral Ligament): Medial femur → medial tibia; resists valgus; attached to medial meniscus
• LCL (Lateral Collateral Ligament): Lateral femur → fibular head; resists varus; NOT attached to lateral meniscus

• Prepatellar bursa — "housemaid's knee"
• Infrapatellar (deep) — "clergyman's knee"
• Baker's cyst (popliteal) — semimembranosus bursa; communicates with joint in adults

• Final 10–15° of extension → lateral femoral condyle moves forward → tibia medially rotates → "screw-home" mechanism; unlocked by popliteus muscle

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3.8 Popliteal Fossa (BD/Snell)

• Superolateral: Biceps femoris
• Superomedial: Semimembranosus + Semitendinosus
• Inferolateral: Lateral head of gastrocnemius
• Inferomedial: Medial head of gastrocnemius
• Roof: Popliteal fascia + skin
• Floor: Popliteal surface of femur → capsule of knee → popliteus

1. Popliteal lymph nodes
2. Small saphenous vein (drains into popliteal vein)
3. Common peroneal nerve (lateral; most superficial)
4. Tibial nerve (medial)
5. Popliteal vein (medial to artery)
6. Popliteal artery (deepest; direct continuation of femoral through adductor hiatus)

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3.9 Nerves of the Lower Limb (Snell — tested heavily)

Femoral Nerve (L2,3,4):

• Emerges lateral to femoral artery below inguinal ligament
• Motor: Quadriceps (knee extension), sartorius, pectineus, iliacus
• Sensory: Anterior + medial thigh, medial leg/foot (saphenous nerve — terminal branch)
• Knee jerk (patellar reflex) — L3,L4

Obturator Nerve (L2,3,4):

• Exits obturator foramen → medial compartment thigh
• Motor: Adductors (longus, brevis, gracilis, obturator externus; part of adductor magnus)
• Sensory: Medial thigh
• Obturator hernia — Howship-Romberg sign (medial thigh pain due to obturator nerve compression)

Sciatic Nerve (L4,5,S1,2,3):

• Largest nerve in body; exits below piriformis in most people
• Divides at apex of popliteal fossa into Tibial + Common Peroneal (Common Fibular)
• Tibial nerve (L4,5,S1,2,3):
  • Posterior leg compartment (all flexors)
  • Plantar aspect of foot via medial + lateral plantar nerves
  • Foot drop does NOT occur with tibial palsy (plantarflexion lost instead)
• Common Peroneal Nerve (L4,5,S1,S2):
  • Winds around neck of fibula → divides into superficial + deep peroneal
  • Superficial peroneal — peroneus longus + brevis (eversion); dorsum of foot sensation
  • Deep peroneal — anterior compartment (dorsiflexors); 1st web space sensation
  • Common peroneal palsy → Foot drop (cannot dorsiflex or evert)

Gluteal Nerves:

• Superior gluteal (L4,5,S1): Gluteus medius, minimus, TFL
• Inferior gluteal (L5,S1,S2): Gluteus maximus

Posterior Cutaneous Nerve of Thigh (S1,2,3): Posterior thigh sensation

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3.10 Leg Compartments (BD Chaurasia)

Anterior Compartment (Deep peroneal nerve, anterior tibial artery):

Lateral Compartment (Superficial peroneal nerve, peroneal artery):

• Peroneus longus — plantar flexion + eversion; crosses plantar foot obliquely to medial cuneiform + 1st metatarsal → supports transverse arch
• Peroneus brevis — plantar flexion + eversion; inserts 5th metatarsal base (avulsion fracture in foot inversion injury)

Posterior Compartment (Tibial nerve, posterior tibial artery):

• Gastrocnemius — plantarflexion; most powerful; sural nerve (S1,S2)
• Soleus — plantarflexion; "second heart" (muscle pump)
• Plantaris — vestigial; long tendon

• Tibialis posterior — plantarflexion + inversion + arch support
• Flexor digitorum longus — flexes toes 2–5; Tom in Tom, Dick + Harry
• Flexor hallucis longus — flexes hallux; Harry; strongest toe flexor; grooves in talus + sustentaculum
• Popliteus — unlocks knee (lateral rotation of femur or medial rotation of tibia)

• Tibialis posterior (tendon)
• Digital flexors (FDL)
• Artery (posterior tibial) + Nerve (tibial)
• Hallucis flexor (FHL)

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3.11 Ankle Joint (Snell/BD)

• Type: Synovial, hinge; mortise and tenon
• Mortise: Formed by inferior tibia + medial malleolus (tibia) + lateral malleolus (fibula)
• Tenon: Body of talus (widest anteriorly — more stable in dorsiflexion)

• Medial (Deltoid) ligament: Strong triangular; tibionavicular, tibiocalcaneal, anterior + posterior tibiotalar; resists eversion
• Lateral ligaments (3 bands):
  • ATFL (anterior talofibular) — weakest; most commonly sprained (inversion sprain)
  • CFL (calcaneofibular)
  • PTFL (posterior talofibular) — strongest

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3.12 Foot Arches (KLM/Snell)

• Bones: Calcaneus → Talus → Navicular → 3 Cuneiforms → Metatarsals 1–3
• Keystone: Talus
• Maintained by: Tibialis posterior, tibialis anterior, flexor hallucis longus, plantar fascia, spring ligament (plantar calcaneonavicular)
• Pes planus (flat foot) — fallen medial arch; tibialis posterior tendon dysfunction most common cause

• Calcaneus → Cuboid → Metatarsals 4,5
• Peroneus longus + brevis maintain

• Across midfoot (cuboid + cuneiforms)
• Maintained by peroneus longus + tibialis posterior

• From calcaneal tuberosity → five slips to toes
• Plantar fasciitis — heel pain at calcaneal insertion; most common cause of heel pain

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3.13 Superficial Veins of the Lower Limb (KLM/BD)

• Great (Long) Saphenous Vein:
  • Starts medial dorsal venous arch → ascends anterior to medial malleolus → medial leg → posterior to medial femoral condyle → saphenous opening (4 cm inferolateral to pubic tubercle) → femoral vein
  • Contains ~10–20 valves; accompanied by saphenous nerve (terminal branch of femoral nerve)
  • Varicose veins most common here
• Small (Short) Saphenous Vein:
  • Lateral dorsal venous arch → posterior to lateral malleolus → posterior leg → pierces popliteal fascia → popliteal vein

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Summary Table: Key Clinical Correlations (Snell)

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• Full vertebral column with ligaments, discs, curvatures, specific vertebrae (atlas/axis)
• Back muscles (superficial extrinsic + deep intrinsic layers, suboccipital triangle)
• Spinal cord, meninges, dermatomes, myotomes, reflexes
• Complete brachial plexus with all 5 nerve palsies (axillary, radial, musculocutaneous, ulnar, median)
• All compartments of arm, forearm, hand with intrinsic muscle innervation
• Lower limb plexuses (femoral, obturator, sciatic with branches)
• All thigh compartments, gluteal muscles + piriformis as landmark
• Femoral triangle and canal, knee joint (ligaments + menisci), popliteal fossa
• Leg compartments, ankle ligaments, foot arches
• Clinical signs: Trendelenburg, Froment, Tinel, Phalen, Lachman, posterior sag