Lower Limb – Ankle & Foot Region Review

Bones of the Ankle

• Tibia, fibula and talus articulate to form the talocrural (ankle) joint.

• Key functional idea: the ankle mortise (distal tib-fib) grips the talar trochlea like a wrench; stability is maximal in dorsiflexion when the wider talar surface is wedged.

Bones of the Foot

• 7 tarsal bones, 5 metatarsals, 14 phalanges.

• Organization

  • Tarsus (proximal): talus, calcaneus, navicular, cuboid, 3 cuneiforms.

  • Metatarsus (middle): numbered I–V (medial → lateral).

  • Phalanges (distal): proximal, middle, distal; hallux has only proximal & distal.

Detailed Bony Landmarks & Significance

Talus

• Head (articulates with navicular).

• Neck: common stress-fracture site in forced dorsiflexion (aviators, snowboarders).

• Medial/lateral malleolar facets—congruent surfaces for mortise.

• Posterior process

  • Medial & lateral tubercles separated by groove for flexor hallucis longus (FHL).

  • Os trigonum = unfused lateral tubercle → pain in dancers during maximal plantarflexion.

• Entire body is covered by articular cartilage; no muscular attachments → vascular supply is precarious, predisposing to avascular necrosis after fracture.

Calcaneus

• Largest tarsal; primary weight-bearing point at heel strike.

• Landmarks

  • Sustentaculum tali (medial): shelf supporting talar head; forms roof of tarsal canal; groove for FHL passes inferiorly.

  • Peroneal (fibular) trochlea (lateral): pulley for fibularis longus & brevis.

  • Posterior surface: calcaneal (Achilles) tendon insertion → Achilles tendinitis, rupture, or calcaneal bursitis.

  • Medial & lateral processes of calcaneal tuberosity: plantar fascia origin & weight distribution during stance.

  • Distal surface articulates with cuboid; superior surface with talus (anterior, middle, posterior facets forming subtalar complex).

Tarsal Canal & Sinus Tarsi

• Canal lies posterior to sustentaculum tali; communicates with sinus tarsi via calcaneal sulcus.

• Clinical pearl: swelling/effusion here disrupts mechanoreceptors → proprioceptive deficits → chronic ankle instability.

• NOT the tarsal tunnel ("Tom Dick | and Nervous Harry" mnemonic for structures deep to flexor retinaculum).

Navicular

• Proximal articulation with talar head; distal with 3 cuneiforms.

• Medial navicular tuberosity: primary insertion of tibialis posterior; often palpable/visible (“fallen navicular” in pes planus).

Cuneiforms

• Medial (largest), intermediate (smallest), lateral (most lateral).

• Serve as keystones in transverse arch; provide wedge-shape stability.

• Articulations

  • Medial: navicular ↔ bases of MT I & II + intermediate cuneiform.

  • Intermediate: navicular ↔ base of MT II ; flanked by other cuneiforms.

  • Lateral: navicular ↔ cuboid + base MT III.

Cuboid

• Lateral mid-foot link between calcaneus & MT IV–V.

• Groove for fibularis longus on plantar surface (mechanical stirrup).

Metatarsals & Phalanges

• Miniature long bones; heads bear body weight during push-off.

• Sesamoids in tendon of flexor hallucis brevis under MT I head → protect FHL & serve as pulleys; can be fractured.

Joints of the Ankle & Foot

• Talocrural (hinge)

• Subtalar (talocalcaneal)

• Transverse tarsal / mid-tarsal (talonavicular + calcaneocuboid)

• Tarsometatarsal (Lisfranc line)

• Metatarsophalangeal (MTP)

• Interphalangeal (IP)

Talocrural Joint—Stability & Ligaments

• Lateral collateral ligaments (inversion sprain complex)

  • Anterior talofibular (ATFL)—first to fail; restrains anterior talar translation.

  • Calcaneofibular (CFL)—resists subtalar inversion.

  • Posterior talofibular (PTFL)—strongest; injured only in severe dislocation.

• Medial (Deltoid) ligament—fan-shaped, rarely torn; resists eversion. Parts: anterior tibiotalar, tibionavicular, tibiocalcaneal, posterior tibiotalar.

• Distal tibiofibular syndesmosis (anterior/posterior tib-fib ligs) → "high-ankle" sprain; widens mortise.

• Motions: \text{dorsiflexion} and \text{plantarflexion} around oblique M–L axis.

Subtalar (Talocalcaneal) Joint

• Second only to SIJ in complexity; primary source of inversion/eversion.

• Part of functional talo-calcaneo-navicular unit (TCN) acting as torque converter between leg & forefoot.

• Ligaments

  • Interosseous talocalcaneal (deep within canal) → key stabilizer.

  • Medial, lateral, posterior talocalcaneal ligs.

  • Plantar calcaneonavicular ("spring") ligament: sling supporting talar head; integrates with tibialis posterior tendon; failure → medial arch collapse (pes planus).

Transverse (Mid-Tarsal) Joints

• Talonavicular (ball-and-socket orientation proximal-plantar → distal-dorsal).

• Calcaneocuboid (saddle/flat; joint line ⟂ lateral foot border).

• Added clinical joints: cubonavicular, naviculocuneiform.

• Ligaments: dorsal talonavicular, bifurcate (“Y”) ligament (calcaneonavicular + calcaneocuboid bands), calcaneocuboid (dorsal, lateral).

• Together with subtalar, mid-tarsal joints allow pronation/supination adaptability during gait.

Tarsometatarsal (Lisfranc) Joints

• Plane joints between distal tarsals & MT bases; provide rigid lever for push-off yet allow twist.

Arches of the Foot

• Medial longitudinal: calcaneus → talus (keystone) → navicular → cuneiforms → MT I–III.

  • Dynamic support: tibialis anterior, tibialis posterior, fibularis longus.

• Lateral longitudinal: calcaneus → cuboid → MT IV–V; flatter, ground-contacting.

• Transverse: cuboid + cuneiforms + MT bases; maintained by fibularis longus & tibialis posterior forming stirrup.

• Passive supports: plantar aponeurosis, spring ligament, long & short plantar ligaments, plantar calcaneocuboid.

Plantar Aponeurosis

• Dense fascia from calcaneal tuberosity → toes; analogous to palmar fascia.

• Supports arches; can develop plantar fasciitis (microtears at medial tubercle after over-pronation or tight triceps surae).

Intrinsic Muscles (Plantar) — 4 Layers

Layer 1

• Abductor hallucis (medial plantar n.) — abducts/flexes hallux; maintains medial arch.

• Flexor digitorum brevis (medial plantar n.) — flexes lateral 4 toes.

• Abductor digiti minimi (lateral plantar n.) — abducts/flexes 5th toe.
  Layer 2

• Quadratus plantae (lateral plantar n.) — straightens pull of FDL; assists toe flexion.

• Lumbricals 1–4

  • #1: medial plantar n.; #2–4: lateral plantar n.

  • Flex MTPs & extend IPs (balanced "table-top" posture).

  • Illustrates dual nerve supply concept (similar to hand).

• Tendons passing: FDL & FHL.
  Layer 3

• Flexor hallucis brevis (medial plantar n.) — two heads with sesamoids; flexes hallux.

• Adductor hallucis (lateral plantar n.) — transverse & oblique heads; adducts hallux, supports transverse arch.

• Flexor digiti minimi brevis (lateral plantar n.).
  Layer 4

• Plantar interossei (PADs, lateral plantar n.) — 3 muscles adduct toes III–V, flex MTP, extend IP.

• Dorsal interossei (DABs, lateral plantar n.) — 4 muscles abduct toes II–IV.

Intrinsic Muscles (Dorsum)

• Extensor digitorum brevis & extensor hallucis brevis (deep fibular n.) — assist toe extension; originate from calcaneus within sinus tarsi.

Segmental & Peripheral Innervation (Lower Limb Recap)

• Major myotomes

  • Hip flexion L2–L3, extension L4–L5.

  • Knee extension L3–L4, flexion L5–S1.

  • Ankle dorsiflexion L4–L5; plantarflexion S1–S2.

  • Foot inversion L4–L5; eversion L5–S1.

• Dermatomal vs. cutaneous nerve fields: overlapping spinal segments vs. discrete peripheral distributions—important in lesion localization (e.g., L5 radiculopathy vs. superficial fibular neuropathy).

Cutaneous & Motor Nerves of the Foot

Dorsum

• Superficial fibular n. → majority dorsal skin + dorsal digital nn. to lateral 4 toes.

• Deep fibular n. → web space between hallux & 2nd toe; motor to EDB/EHB.

• Sural n. → posterolateral border & lateral dorsum via lateral dorsal cutaneous n.

• Saphenous n. → medial ankle & foot margin.
  Plantar

• Medial plantar n. (analogous to median): medial 3.5 digits, abductor hallucis, FHB, FDB, 1st lumbrical.

• Lateral plantar n. (analogous to ulnar): lateral 1.5 digits & most intrinsic muscles.

• Medial calcaneal branches (from tibial) → heel skin.

Vascular Supply

Dorsal (from anterior tibial → dorsalis pedis)

• Branches: lateral tarsal a., arcuate a. (→ dorsal metatarsal & digital aa.), deep plantar a. (dives through 1st interspace to plantar arch).
  Plantar (from posterior tibial)

• Medial plantar a. (smaller) → digital branches.

• Lateral plantar a. → curves medially to join deep plantar a., forming deep plantar arch → plantar metatarsal & digital aa.

Clinical Blue-Box Highlights

• Calcaneal fracture: high-energy axial load (falls); Bohler angle ↓ on X-ray.

• Talar neck fracture: forced dorsiflexion; risk of AVN.

• Metatarsal stress fractures: dancers, military recruits; 2nd MT common.

• Os trigonum syndrome: posterior ankle impingement in ballet & soccer.

• Sesamoiditis/fracture under MT I: turf toe, runners.

• Achilles tendinopathy/rupture: positive Thompson test; absent plantarflexion & calcaneal tendon reflex.

• Gastrocnemius strain (“tennis leg”): sudden push-off.

• Pes planus: collapse of medial arch due to spring ligament/tibialis posterior insufficiency.

• Hallux valgus (bunion): lateral deviation of hallux → altered weight bearing.

• Hammer/claw toes: MTP extension with PIP/DIP flexion due to intrinsic/extrinsic imbalance.

• Clubfoot (talipes equinovarus): congenital; foot inverted, plantarflexed, adducted.

• Posterior tibial pulse: palpated posterior to medial malleolus; diminished in PVD.

Conceptual & Functional Connections

• Foot arches function as trusses & springs; during gait the subtalar joint "locks" in supination for rigid push-off, "unlocks" in pronation for shock absorption.

• Tibialis posterior + fibularis longus form a stirrup supporting transverse arch—demonstrates complementary action of medial & lateral compartment muscles.

• Plantar intrinsic muscles mirror hand intrinsics; their coordinated activity stabilizes toes during stance, preventing hammer/claw deformity.

• Ligamentous integrity (ATFL/CFL vs. Deltoid) explains higher frequency of inversion sprains.

• Neural & vascular pathways wrap around malleoli; tight casts or edema threaten deep fibular n. (anterior compartment) or posterior tibial art/nerve (tarsal tunnel).

Quick-Reference Numbers & Mnemonics

• "Tom, Dick, \text{and Nervous} Harry" (tibialis posterior, flexor digitorum longus, posterior tibial a./v./n., flexor hallucis longus) in tarsal tunnel.

• "PAD & DAB": Plantar = ADduct, Dorsal = ABduct interossei.

• 7 tarsals, 5 metatarsals, 14 phalanges → 26 bones per foot.

• Weight distribution during quiet standing: \approx 60\% calcaneus, 40\% metatarsal heads.