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COMPLETE NOTES: Lower Limb Anatomy (MS-A-047 to MS-A-066)

Human Anatomy - C2K23 Year-01

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MS-A-047 | MUSCLES OF THE LEG

Compartments of the Leg

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ANTERIOR COMPARTMENT

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LATERAL COMPARTMENT

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POSTERIOR COMPARTMENT

Superficial Group

Triceps surae = Gastrocnemius + Soleus (share the Achilles tendon)

Deep Group

Mnemonic for deep posterior muscles (Tom, Dick AND Harry): Tibialis posterior, flexor Digitorum longus, posterior tibial Artery + tibial Nerve, flexor Hallucis longus

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MS-A-048 | NEUROVASCULAR SUPPLY OF THE LEG

Nerves of the Leg

Vessels of the Leg

Clinical Conditions

Compartment Syndrome

• Increased pressure within a closed fascial compartment
• Causes: fracture, crush injury, reperfusion, tight cast
• 6 P's: Pain (especially on passive stretch), Pressure (tense compartment), Paresthesia, Paralysis, Pallor, Pulselessness (late sign)
• Management: Urgent fasciotomy (all 4 compartments of leg)
• Anterior compartment most commonly affected

Foot Drop

• Inability to dorsiflex the foot
• Cause: Damage to common peroneal (fibular) nerve at fibular neck
• Causes: fibular neck fracture, prolonged pressure (leg crossing), plaster cast
• Patient walks with high-stepping (steppage) gait
• Paralysis of anterior and lateral compartment muscles
• Sensory loss: dorsum of foot and 1st web space

Cutaneous Nerves and Veins of the Leg

Cutaneous Nerves

• Medial surface: Saphenous nerve (femoral nerve branch) - runs with great saphenous vein
• Lateral surface: Sural nerve - lateral side of leg and foot
• Lateral upper leg: Lateral cutaneous nerve of calf (common peroneal branch)
• Anterior: Superficial peroneal nerve (distal 2/3 of anterior leg + dorsum of foot)

Superficial Veins

• Great (long) saphenous vein: Begins dorsal venous arch of foot, passes anterior to medial malleolus, runs up medial aspect of leg/thigh, drains into femoral vein at saphenofemoral junction (4 cm below and lateral to pubic tubercle)
• Small (short) saphenous vein: Passes posterior to lateral malleolus, runs up back of leg, drains into popliteal vein at popliteal fossa

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MS-A-049 | FLEXOR, EXTENSOR, AND PERONEAL RETINACULA

Retinacula at the Ankle

Extensor Retinacula

Flexor Retinaculum (Laciniate Ligament)

• Spans from medial malleolus to medial surface of calcaneus
• Forms the tarsal tunnel
• Structures (medial to lateral) - "Tom, Dick And Very Nervous Harry":
  • Tibialis posterior tendon
  • Digitorum longus tendon
  • posterior tibial Artery
  • tibial Vein (posterior tibial)
  • tibial Nerve
  • flexor Hallucis longus tendon
• Tarsal tunnel syndrome: compression of tibial nerve → pain/tingling in sole and toes

Peroneal Retinacula

Calcaneal (Achilles) Tendon - Tendo Calcaneus

• Formed by union of tendons of gastrocnemius + soleus (triceps surae)
• Plantaris tendon joins medially (vestigial)
• Inserts into middle 1/3 of posterior calcaneal surface
• No synovial sheath - surrounded by paratenon
• Pre-Achilles bursa (retrocalcaneal bursa) lies between tendon and calcaneus
• Clinical: Achilles tendon rupture - most common in 30-50 year old males, squash/tennis players; Thompson (Simmonds) test positive

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MS-A-050 | TIBIOFIBULAR JOINTS

Superior (Proximal) Tibiofibular Joint

• Type: Plane (gliding) synovial joint
• Articulation: Head of fibula with inferior facet on posterior lateral tibial condyle
• Ligaments: Anterior and posterior tibiofibular ligaments (superior), fibular collateral ligament reinforces
• Nerve supply: Common peroneal and tibial nerves
• Movement: Slight gliding during ankle movements

Inferior (Distal) Tibiofibular Joint

• Type: Fibrous joint (syndesmosis) - NOT synovial
• Articulation: Fibular notch of tibia + distal fibula
• Ligaments: Anterior inferior tibiofibular ligament (AITFL), Posterior inferior tibiofibular ligament (PITFL), Interosseous ligament, Transverse tibiofibular ligament
• Nerve supply: Deep peroneal + sural nerves
• Movement: Slight spread/spring during dorsiflexion (fibula moves laterally and rotates)
• Clinical: Diastasis (widening) in Maisonneuve fracture / high ankle sprain

Interosseous Membrane

• Connects interosseous borders of tibia and fibula
• Fibres run downward + laterally from tibia to fibula
• Transmits forces from fibula to tibia
• Allows passage of anterior tibial vessels anteriorly (via oval opening near upper margin)

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MS-A-051 | ANKLE JOINT

Type

• Synovial, hinge (ginglymus) joint
• Also called talocrural joint

Articulating Surfaces

• Above: Lower end of tibia (tibial plafond) + medial malleolus (tibia) + lateral malleolus (fibula)
• Below: Superior (trochlear) surface of talus - wider anteriorly
• The mortise is formed by the two malleoli gripping the talus

Ligaments

Movements and Muscles

• Dorsiflexion (20°): Tibialis anterior, EDL, EHL, peroneus tertius
• Plantarflexion (50°): Gastrocnemius, soleus, tibialis posterior, FDL, FHL, fibularis muscles

Stability Factors

1. Bony mortise (most important) - talus is wider anteriorly, more stable in dorsiflexion
2. Medial (deltoid) ligament - strong
3. Lateral ligaments (ATFL, CFL, PTFL)
4. Tendons around the joint
5. Capsule

Nerve Supply

• Articular branches from deep peroneal, superficial peroneal, tibial, sural, saphenous nerves

Clinical Conditions

• Pott's fracture: Fracture-dislocation of ankle; eversion injury
• Lateral ankle sprain: Inversion injury → ATFL torn first (most common ligament injury in body)
• Dupuytren's fracture: Fracture of fibula with tearing of deltoid ligament
• Osteoarthritis: Common in post-traumatic setting

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MS-A-052 | PLANTAR FASCIA

Plantar Aponeurosis - Formation and Attachments

• Thick band of dense fibrous connective tissue
• Proximal attachment: Medial tubercle of calcaneus (posterior)
• Distal attachment: Divides into 5 slips → base of proximal phalanges, flexor tendon sheaths, skin
• Three parts: central (thickest), medial, lateral

Functions

• Supports medial longitudinal arch
• Protects plantar vessels and nerves
• Acts as a "windlass mechanism" - tightens when toes dorsiflexed, raises the arch, stabilizes foot for push-off

Plantar Fasciitis

• Most common cause of heel pain
• Inflammation/degeneration at calcaneal attachment
• Risk factors: Obesity, prolonged standing, flat foot (pes planus), tight calf muscles, ill-fitting footwear, athletes (runners)
• Signs & Symptoms:
  • Pain at medial aspect of heel (plantar surface)
  • Worst in the morning (first steps) and after prolonged rest ("start-up pain")
  • Improves with activity then worsens again
  • Point tenderness at medial calcaneal tubercle
  • Tinel's sign may be positive
• Anatomy of pain: Micro-tears at calcaneal enthesis, reactive inflammation
• X-ray: May show calcaneal heel spur (but spur ≠ cause of pain)
• Management: Rest, NSAIDs, heel cups, physiotherapy, night splints, steroid injection; surgery (fasciotomy) rarely needed

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MS-A-053 | MUSCLES OF THE FOOT

Dorsum of Foot

Sole of Foot - 4 Layers

Layer 1 (Most Superficial)

Layer 2

Layer 3

Layer 4 (Deepest)

Key point: The axis of abduction/adduction of the foot is the 2nd toe (unlike hand which uses 3rd finger)

Interossei and Lumbricals: Same action as in hand - flex MTP joints and extend IP joints. Lumbricals also prevent "claw toe" deformity.

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MS-A-054 | SMALL JOINTS OF THE FOOT

Subtalar (Talocalcaneal) Joint

• Type: Synovial, modified plane joint (gliding)
• Articulation: Inferior talus with superior calcaneus (3 facets)
• Movements: Inversion and eversion
• Ligaments: Medial, lateral, posterior talocalcaneal, interosseous talocalcaneal

Talocalcaneonavicular Joint

• Type: Ball and socket (functionally)
• Head of talus articulates with navicular + calcaneus + plantar calcaneonavicular (spring) ligament
• Spring ligament supports head of talus; if weak → flat foot

Midtarsal (Transverse Tarsal / Chopart's) Joint

• Between talus/calcaneus proximally and navicular/cuboid distally
• Allows gliding movements contributing to inversion/eversion

Tarsometatarsal (Lisfranc) Joints

• Type: Plane synovial joints
• Clinical: Lisfranc injury - common in football, equestrians

Metatarsophalangeal (MTP) Joints

• Type: Condyloid synovial joints
• Movements: Flexion, extension, abduction, adduction
• Sesamoid bones in FHB tendons at 1st MTP

Interphalangeal Joints

• Type: Hinge synovial joints
• Proximal IP (PIP) and Distal IP (DIP)
• Hallux has only one IP joint

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MS-A-055 | ARCHES OF THE FOOT

Types of Arches

1. Medial Longitudinal Arch (MLA) - Higher

• Bones: Calcaneus, talus, navicular, 3 cuneiforms, medial 3 metatarsals
• Keystone: Talus (receives body weight)
• Static supports: Plantar calcaneonavicular (spring) ligament (most important), plantar fascia, long plantar ligament
• Dynamic supports: Tibialis posterior (main), FHL, FDL

2. Lateral Longitudinal Arch - Lower (nearly flat)

• Bones: Calcaneus, cuboid, lateral 2 metatarsals
• Static supports: Long plantar ligament, short plantar ligament (plantar calcaneocuboid), plantar fascia
• Dynamic supports: Fibularis longus and brevis, FDL

3. Transverse Arch

• Passes across metatarsal bases and cuneiforms
• Keystone: Intermediate cuneiform
• Supports: Fibularis longus tendon (crosses sole), adductor hallucis (transverse head), deep transverse metatarsal ligament

Clinical Conditions

Flat Foot (Pes Planus)

• Loss of medial longitudinal arch
• Causes: Ligamentous laxity (physiological in children under 3), tibialis posterior dysfunction, spring ligament tear, obesity
• Types: Flexible (arch reforms on tip-toes) vs Rigid (fixed deformity)
• Pain on medial side of ankle/foot; foot fatigue

Claw Foot (Pes Cavus)

• Exaggerated arches + claw toes
• Causes: Neurological (Charcot-Marie-Tooth disease, Friedrich's ataxia, polio), idiopathic
• Features: high arch, dorsal foot skin hyperkeratosis, claw toes (MTP hyperextension + IP flexion)

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MS-A-056 | RETINACULA OF THE FOOT

Fibrous Flexor Sheaths

• Osteofibrous tunnels enclosing flexor tendons on plantar surface of toes
• Prevent bowstringing during toe flexion
• Contain synovial sheaths for lubrication
• Annular (A) and cruciate (C) pulleys

Extensor Expansions (Dorsal Digital Expansions)

• Triangular aponeuroses on dorsum of toes
• Formed by: long extensor tendons (central slip) + interossei + lumbricals
• Allow simultaneous MTP flexion and IP extension (intrinsic-plus position)

Synovial Flexor Sheaths of Foot

• Individual digital sheaths for each toe
• Communicate with bursae near attachment sites

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MS-A-057 | NEUROVASCULAR SUPPLY OF THE FOOT

Arteries of the Foot

Dorsalis Pedis Artery

• Continuation of anterior tibial artery at ankle (crosses inferior extensor retinaculum)
• Course: lateral to EHL tendon; over dorsum of foot
• Branches: Medial and lateral tarsal arteries, arcuate artery (→ 2nd-4th dorsal metatarsal arteries), 1st dorsal metatarsal artery, deep plantar artery (joins plantar arch)
• Palpation: On dorsum of foot, lateral to EHL tendon, proximal to 1st intermetatarsal space
• Clinical significance: Absent in ~10-12% normal population; important marker of peripheral arterial disease; palpated routinely; lost in critical ischemia of foot

Plantar Arteries

• Posterior tibial artery passes behind medial malleolus → divides under flexor retinaculum into:
  • Medial plantar artery (smaller): Runs along medial side of sole between abductor hallucis and FDB; supplies medial toes
  • Lateral plantar artery (larger): Crosses sole obliquely to form plantar arch (with deep plantar artery); supplies lateral toes and plantar arch → plantar metatarsal arteries → digital arteries

Nerves of the Foot

Medial Plantar Nerve (equivalent of median nerve of hand)

• Accompanies medial plantar artery
• Motor: Abductor hallucis, FDB, FHB, 1st lumbrical
• Sensory: Medial 3.5 toes (plantar surface) + medial sole

Lateral Plantar Nerve (equivalent of ulnar nerve of hand)

• Accompanies lateral plantar artery
• Motor: All other intrinsic muscles (quadratus plantae, abductor digiti minimi, lumbricals 2-4, all interossei, adductor hallucis, flexor digiti minimi)
• Sensory: Lateral 1.5 toes + lateral sole

Sural Nerve

• Lateral side of foot and little toe

Saphenous Nerve

• Medial side of foot

Superficial Peroneal Nerve

• Most of dorsum of foot (except 1st web space + lateral border)

Deep Peroneal Nerve

• 1st web space skin (dorsum); EDB and EHB muscles

Cutaneous Nerves and Dermatomes of Foot

• Dorsum: Superficial peroneal nerve (main) + deep peroneal (1st web space) + sural (lateral border) + saphenous (medial border)
• Sole: Medial plantar (medial 3.5 toes + medial sole) + lateral plantar (lateral 1.5 toes + lateral sole)

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MS-A-058 | ARTERIAL AND VENOUS DRAINAGE OF LOWER LIMB

Superficial Veins

Great Saphenous Vein (GSV)

• Origin: Medial end of dorsal venous arch of foot
• Course: Anterior to medial malleolus → medial surface of leg → posterior to medial condyle of femur → anteromedial thigh → saphenous opening (4 cm below and lateral to pubic tubercle) → drains into femoral vein (saphenofemoral junction)
• Tributaries: Superficial epigastric, superficial circumflex iliac, superficial external pudendal veins (at saphenofemoral junction); accessory saphenous veins
• Communications: Multiple perforating (communicating) veins connect to deep veins; valves direct blood from superficial → deep
• Clinical: Varicose veins (incompetent valves); used as coronary artery bypass graft conduit; line of saphenous nerve

Small Saphenous Vein (SSV)

• Origin: Lateral end of dorsal venous arch
• Course: Posterior to lateral malleolus → midline of calf → popliteal fossa → drains into popliteal vein (saphenopopliteal junction)
• Communications: Drains lateral calf; communicates with GSV via thigh veins

Concept Map Summary

Dorsal venous arch of foot
├── Medially → Great saphenous vein → Femoral vein (at SFJ in femoral triangle)
└── Laterally → Small saphenous vein → Popliteal vein (at SPJ in popliteal fossa)

Factors Favoring Venous Return of Lower Limb

1. Calf muscle pump (most important) - gastrocnemius/soleus contractions compress deep veins
2. Venous valves - prevent retrograde flow
3. Foot pump - compression of plantar venous plexus on weight bearing
4. Arterial pulsation (minor effect)
5. Respiratory pump - inspiration decreases intrathoracic pressure, increases abdominal pressure, aids venous return from lower limb
6. Gravity - when legs are elevated

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MS-A-059 | DEEP VENOUS THROMBOSIS (DVT) & LOWER LIMB ARTERIES

Deep Venous Thrombosis

Anatomical Basis of Formation - Virchow's Triad

1. Venous stasis (immobility, heart failure, pregnancy, long-haul flights)
2. Hypercoagulability (pregnancy, malignancy, thrombophilia, OCP)
3. Endothelial injury (trauma, surgery, IV cannula)

Signs and Symptoms

• Unilateral leg swelling
• Calf pain and tenderness
• Warmth and erythema
• Homan's sign (pain on dorsiflexion) - not reliable
• Dilated superficial veins
• Low-grade fever

Investigations

• D-dimer (sensitive, not specific); Wells score for pre-test probability
• Gold standard: Compression duplex ultrasound

Complications

• Pulmonary embolism (PE) - most dangerous
• Post-thrombotic syndrome (chronic venous insufficiency)

Management

• Anticoagulation (LMWH → DOAC/warfarin)
• Compression stockings
• IVC filter in selected cases

Clinical Correlations: Lower Limb Arteries

Intermittent Claudication

• Pain in calf (or thigh/buttock) on walking, relieved by rest
• Due to occlusive arterial disease (atherosclerosis)
• ABI (Ankle-Brachial Index): Normal >1.0; Claudication 0.4-0.9; Rest pain <0.4; Tissue loss <0.2
• Fontaine stages: I (asymptomatic) → II (claudication) → III (rest pain) → IV (ulceration/gangrene)

Collateral Circulation

• Critical after occlusion of major vessels
• Femoral artery: profunda femoris collaterals
• Popliteal artery: geniculate anastomoses

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MS-A-060 | LYMPHATIC DRAINAGE OF THE LOWER LIMB

Superficial Lymphatics

• Follow great saphenous vein → drain into superficial inguinal lymph nodes (horizontal group: drain perineum, gluteal region, lower trunk; vertical group: drain leg along GSV)
• Follow small saphenous vein → popliteal nodes → deep inguinal nodes

Deep Lymphatics

• Follow deep vessels (femoral, popliteal) → popliteal nodes → deep inguinal nodes → external iliac nodes → common iliac nodes → lumbar (para-aortic) nodes

Inguinal Lymph Nodes

• Superficial inguinal nodes: In femoral triangle below inguinal ligament; drain most of lower limb, perineum, lower abdominal wall, gluteal region
• Deep inguinal nodes: Medial to femoral vein; drain glans penis/clitoris, deep structures; receive efferents from popliteal nodes

Clinical: Lymphedema

• Obstruction of lymphatics → painless pitting edema
• Primary (Milroy's disease) vs Secondary (filariasis, malignancy, post-radiation)

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MS-A-061 | CUTANEOUS DERMATOMES & NERVE SUPPLY OF LOWER LIMB

Dermatomes of Lower Limb

Clinical Correlates of Lower Limb Nerve Injuries

Femoral Nerve Injury (L2, L3, L4)

• Cause: Penetrating groin wounds, inguinal hernia repair, pelvic fractures, psoas hematoma, lithotomy position
• Motor loss: Quadriceps femoris (knee extension), iliacus (hip flexion), sartorius, pectineus
• Sensory loss: Anterior/medial thigh and medial leg (saphenous nerve)
• Reflex: Loss of knee jerk (L3, L4)
• Gait: Inability to extend knee; hyperextend knee to "lock" it; difficulty climbing stairs

Sciatic Nerve Injury (L4, L5, S1, S2, S3)

• Cause: Posterior hip dislocation, deep IM injection (lower outer quadrant), hip replacement, pelvic fractures
• Motor loss: Hamstrings + all muscles below knee (tibial and peroneal)
• Sensory loss: Most of leg and foot (except medial strip by saphenous)
• High injury: Complete loss of all movement below knee + posterior thigh
• Low (popliteal) injury: Acts like combined tibial + peroneal nerve injury

Common Peroneal (Fibular) Nerve Injury (L4, L5, S1, S2)

• Cause: Fibular neck fracture, leg crossing, tight cast, compartment syndrome
• Motor loss: All anterior and lateral compartment muscles → foot drop + loss of eversion
• Sensory loss: Dorsum of foot, lateral leg, 1st web space
• Deformity: Foot drop + inversion (tibialis posterior unopposed)
• Gait: Steppage (high-stepping) gait

Tibial Nerve Injury (L4, L5, S1, S2, S3)

• Cause: Knee dislocation, posterior compartment syndrome, tarsal tunnel
• Motor loss: Posterior compartment of leg + all intrinsic foot muscles
• Sensory loss: Sole of foot, heel
• Deformity: Calcaneovalgus (calcaneal gait) + loss of toe flexion
• High injury: Loss of plantarflexion + inversion; claw toes not present initially

Obturator Nerve Injury (L2, L3, L4)

• Cause: Obturator hernia, pelvic fractures, prolonged labor
• Motor loss: Adductors of thigh (adductor longus, brevis, magnus, gracilis, obturator externus)
• Sensory loss: Medial thigh
• Gait: Wide-based, scissoring in severe adductor spasm

Reflexes

• Knee jerk (patellar reflex): Tap patellar tendon → quadriceps contraction → knee extension. Nerve roots: L3, L4 (femoral nerve). Tests L3-L4 integrity.
• Ankle jerk (Achilles reflex): Tap Achilles tendon → gastrocnemius/soleus contraction → plantarflexion. Nerve roots: S1, S2 (tibial nerve). Tests S1-S2 integrity.
• Plantar reflex (Babinski test): Stroke lateral sole from heel to ball of foot then across to big toe. Normal: plantarflexion of toes (downgoing). Abnormal (Babinski positive/extensor): dorsiflexion of big toe + fan out of other toes → upper motor neuron lesion.

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MS-A-062 | TOPOGRAPHICAL AND RADIOLOGICAL ANATOMY OF LOWER LIMB

Surface Markings - Key Nerves and Vessels

• Femoral artery: Midinguinal point; runs to adductor canal
• Femoral vein: Medial to femoral artery in femoral triangle
• Popliteal artery: Vertical line in midline of popliteal fossa
• Posterior tibial artery: Behind medial malleolus
• Common peroneal nerve: Around neck of fibula (palpable)
• Sciatic nerve: Midpoint between ischial tuberosity and greater trochanter

Bony Landmarks

• ASIS, PSIS, iliac crest: Pelvis
• Greater trochanter: Lateral hip
• Patella: Anterior knee
• Tibial tuberosity: Proximal tibia
• Head of fibula: Lateral knee (common peroneal nerve here)
• Medial and lateral malleoli: Ankle
• Sustentaculum tali: Below medial malleolus (FHL passes underneath)
• Base of 5th metatarsal: Lateral foot (Jones fracture here)

Cross-sectional Anatomy of Leg (at mid-shaft level)

• Tibia medially (superficial, subcutaneous)
• Fibula posterolaterally
• Anterior compartment: muscles + deep peroneal nerve + anterior tibial vessels
• Lateral compartment: peroneal muscles + superficial peroneal nerve
• Posterior compartment (deep): deep flexors + tibial nerve + posterior tibial + peroneal vessels
• Posterior (superficial): triceps surae

Radiology

• X-ray: AP and lateral views; assess for fractures, joint space, alignment
• CT scan: Best for complex fractures (calcaneus, Lisfranc, tibial plateau)
• MRI: Ligament, tendon, cartilage injuries; bone stress fractures
• Ultrasound: DVT, tendon ruptures

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MS-A-063 | BONE FRACTURES

General Principles

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MS-A-064 | JOINT DISLOCATIONS

General Principles

Shoulder Joint Dislocation

• Most commonly dislocated joint in body
• Anterior dislocation (95%): Fall on abducted, externally rotated arm; axillary nerve at risk (deltoid paralysis, loss of sensation "regimental badge" area); Hill-Sachs lesion (posterior humeral head notch) + Bankart lesion (inferior glenoid labrum tear)
• Posterior dislocation (rare): Epileptic fit, electric shock, fall on internally rotated arm; often missed on AP X-ray (lightbulb sign)
• Inferior (luxatio erecta): Very rare; arm fixed above head
• Management: Reduction (Kocher's, Hippocratic, Cunningham technique) → immobilization → physio; recurrent → Bankart repair/Latarjet procedure

Elbow Joint Dislocation

• Most common dislocation in children
• Posterior dislocation (most common) - fall on outstretched hand
• Risk: brachial artery, median + ulnar nerve injury
• Terrible triad: Posterior dislocation + radial head fracture + coronoid fracture
• Management: Closed reduction under sedation; assess neurovascular status

Interphalangeal Joint of Hand

• Usually dorsal (PIP most common)
• Risk: volar plate tear, collateral ligament injury
• Management: Closed reduction + buddy strapping; assess for fracture-dislocation

Hip Joint Dislocation

• Posterior (90%): Flexed, adducted, internally rotated hip (dashboard injury)
• Femoral head exits through greater sciatic foramen
• Risk: Sciatic nerve injury (especially common peroneal division), avascular necrosis of femoral head (within 6 hours is critical)
• X-ray: Femoral head above and lateral acetabulum in anterior; below and medial in posterior
• Management: Emergency closed reduction within 6 hours to reduce AVN risk; traction

Knee Joint Dislocation

• High energy injury; tibiofemoral dislocation
• Risk: Popliteal artery injury (must rule out), common peroneal nerve, cruciate ligaments, collaterals
• Reduce immediately; arteriogram or CT angiogram; repair ligaments

Ankle Joint Dislocation

• Rare in isolation (usually associated with fractures - Pott's/Maisonneuve)
• Lateral (most common with fractures); posteromedial
• Risk: skin pressure necrosis (must reduce urgently)
• Management: Urgent reduction; assess for open injury

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MS-A-065 | DEVELOPMENT OF MUSCLES (Embryology)

Skeletal Muscle Development

• Origin: Somites → dermomyotomes → myotomes
• Process: Somitic myotomes segment around week 4-5; each myotome = one spinal segment
• Axial muscles: Each myotome gives epimere (back/extensor muscles) and hypomere (ventrolateral/flexor muscles)
• Myotome concept: Each muscle group receives innervation from corresponding spinal segments → basis for segmental innervation/dermatomes

Cardiac Muscle Development

• Origin: Splanchnic mesoderm (cardiogenic plate)
• Cardiac myoblasts differentiate into cardiac muscle; forms heart tube from week 3
• Innervated by autonomic (not somatic) nervous system

Smooth Muscle Development

• Origin: Splanchnic mesoderm (gut, vessels), neural crest (pupil, arrector pili), somatic mesoderm
• Not derived from myotomes
• (Detailed coverage in respective system modules)

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MS-A-066 | DEVELOPMENT OF LIMB

Limb Development

• Begins week 4 (upper limb) and week 5 (lower limb); upper limb 1-2 days ahead
• Limb buds: Lateral plate mesoderm core covered by ectoderm
• Apical ectodermal ridge (AER): Thickened ectoderm at tip of bud; drives proximodistal elongation; signals FGFs (FGF8, FGF10)
• Zone of polarizing activity (ZPA): Posterior mesenchyme; controls anteroposterior axis via Sonic hedgehog (Shh)
• Non-AER ectoderm: Dorsoventral patterning (Wnt7a = dorsal; BMP = ventral)
• Limb axes:
  • Proximodistal: AER (FGF)
  • Anteroposterior: ZPA (Shh)
  • Dorsoventral: non-AER ectoderm (Wnt7a)
• Rotation: Lower limb rotates medially (so knee points anteriorly, big toe is medial) during development
• Apoptosis: Interdigital necrosis removes webbing (programmed cell death via BMPs); failure = syndactyly

Limb Growth after Birth

• Long bones grow at epiphyseal plates (growth plates)
• Growth continues until skeletal maturity (~18-20 years)
• Ossification: endochondral

Embryological Basis of Cutaneous Innervation

• Each somite-derived myotome is accompanied by its dermatome (corresponding skin area)
• As limb bud elongates, dermatomes are dragged distally in sequential strips
• This produces the characteristic axial lines (preaxial and postaxial borders)
• Preaxial border (thumb/hallux side): L4
• Postaxial border (little toe side): S1

Common Limb Developmental Anomalies

• Amelia: Absence of limb
• Hemimelia: Absence of distal limb
• Polydactyly: Extra digit (failure of apoptosis or duplication)
• Syndactyly: Fused digits (failure of interdigital apoptosis)
• Clubfoot (talipes equinovarus): Most common congenital foot deformity - equinus + varus + adductus; multifactorial; treated with Ponseti method

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QUICK REFERENCE SUMMARY TABLE

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