Tarsus

TERMINOLOGY

Definitions

• 3 major divisions

Hindfoot : Calcaneus and talus

Midfoot : Navicular, cuneiforms, and cuboid

Forefoot : Metatarsals and phalanges
• 2 columns

Medial column : Talus, navicular, cuneiforms 1-3, digits 1-3

Lateral column : Calcaneus, cuboid, digits 4 and 5
• Some authors use 2 columns in hind and midfoot but divide forefoot into 3 columns

Medial column: 1st toe

Middle column: 2nd-4th toes

Lateral column: 5th toe

IMAGING ANATOMY

Overview

• Alignment of foot can only be assessed on weight-bearing radiographs

Arches of Foot

• Foot is arched from posterior to anterior and from medial to lateral
• Transverse arch of foot

Cuneiform bones form keystone of arch due to triangular shape

Major supporting structures of transverse arch

– Spring ligament

– Lisfranc ligament and intermetatarsal ligaments

– Intertarsal ligaments
• Longitudinal arch of foot

From posterior process calcaneus to metatarsal heads

Medial side is higher than lateral

Apex of arch is at navicular and cuneiforms

Metatarsals slant downward from apex of arch to metatarsophalangeal (MTP) joint

– This is called inclination angle

– Inclination angle decreases from 20° at 1st to 5° at 5th metatarsal

Major supporting structures of longitudinal arch

– Plantar fascia

– Long and short plantar ligaments

– Spring ligament

– Posterior tibial tendon, peroneus longus tendon
• Radiographic assessment of normal longitudinal arch

Evaluate talometatarsal alignment

– Normal: Axis of talus continues along axis of 1st metatarsal

– Pes planus: Axis of talus points below axis of 1st metacarpal due to flattened arch

– Pes cavus: Axis of talus points above axis of 1st metacarpal due to exaggerated arch

Distribution of Weight Bearing

• 50% of weight is borne on subtalar joint and calcaneus
• Remainder is transmitted via arch anteriorly to MTP joints, greatest weight on 1st toe

Bony Anatomy

• Cuboid bone

Roughly cuboidal shape

1 ossification center: Ossifies between 9th fetal month and 6 months of age

Articulates with calcaneus, navicular, 3rd cuneiform, and 4th and 5th metatarsals, rarely head of talus

– Dorsal ligaments (calcaneocuboid, cubonavicular, cuneocuboid, cubometatarsal) strengthen each of these articulations

– Short and long plantar ligaments attach to plantar surface

Sulcus at lateral margin, under which passes peroneus longus tendon

5th metatarsal base extends beyond lateral margin
• Navicular bone

Curved shape, concave proximally and convex distally

1 ossification center: Ossifies in 3rd year of life

Articulates with talus, cuboid, cuneiforms

– Dorsal ligaments strengthen each of these articulations

– Single facet proximally for articulation with head of talus

– 3 facets distally for cuneiform articulations

– 1 facet laterally for articulation with cuboid

– Connected to anterior process of calcaneus by bifurcate ligament

– Connected to sustentaculum tali by spring ligament

Large median eminence for attachment of posterior tibial tendon is located more plantar than main body of navicular
• Cuneiform bones

Wedge-shaped with base of wedge at dorsal surface of 2nd and 3rd cuneiforms, dorsomedial surface of 1st cuneiform

In combination, form arch

1st cuneiform (medial cuneiform)

– Articulates with navicular, 2nd cuneiform, 1st metatarsal

– 1 or 2 ossifications centers: Ossify in 2nd year of life

2nd cuneiform (middle or intermediate cuneiform)

– Articulates with navicular, 1st and 3rd cuneiforms, 2nd metatarsal

– Smallest of cuneiforms

– 1 ossification center: Ossifies in 3rd year of life

3rd cuneiform (lateral cuneiform)

– Articulates with navicular, 2nd cuneiform, cuboid, 3rd metatarsal
• Metatarsal bones

2 ossifications centers: Shaft ossifies in 9th prenatal week, epiphysis in 3rd-4th years of life

– 1st metatarsal has epiphysis at proximal end, others at distal end

2nd-5th metatarsals have articulations at bases with adjacent metatarsals

1st metatarsal

– Largest of metatarsals

– Articulates with 1st cuneiform, 1st proximal phalanx, sesamoids of metatarsal head

– Variable articulation with 2nd metatarsal base

2nd-3rd metatarsals

– Articulate with respective cuneiforms and proximal phalanges

– 2nd metatarsal base recessed relative to 1st and usually 3rd

4th-5th metatarsals

– Articulate with cuboid and respective proximal phalanges

– Styloid process of 5th metatarsal extends lateral to cuboid
• Phalanges

1st toe is biphalangeal, other toes are triphalangeal

5th toe sometimes has failure of segmentation of middle and distal phalanges

2 ossification centers: Shaft ossifies 9th-15th prenatal weeks, epiphysis 2nd-8th years

Musculature

• Plantar muscles : 4 muscle layers, numbered from superficial to deep

1st layer: Abductor hallucis, flexor digitorum brevis, abductor digiti minimi

2nd layer: Quadratus plantae (flexor accessorius), flexor digitorum and hallucis longus tendons, lumbricals

3rd layer: Flexor hallucis brevis, adductor hallucis, flexor digiti minimi brevis, tibialis posterior tendon

4th layer: Plantar interossei (3), dorsal interossei (4)

Peroneus longus tendon courses across all layers, from superficial plantar laterally to deep plantar medially
• Dorsal muscles : 2 muscle layers

Superficial layer: Tibialis anterior tendon, extensor hallucis longus tendon, extensor digitorum longus tendon, peroneus tertius tendon

Deep layer: Extensor hallucis brevis, extensor digitorum brevis

In forefoot, long and short extensors run side by side in single layer

Compartments

• Plantar compartments: 4 plantar compartments are located deep to plantar fascia

Divided by fascial layers

Lateral and medial intermuscular septa determine major compartment divisions

Medial plantar compartment

– Contains abductor hallucis, flexor hallucis longus, and flexor hallucis brevis tendons

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Apr 9, 2020 | Posted by admin in MUSCULOSKELETAL IMAGING | Comments Off

TERMINOLOGY

Definitions

IMAGING ANATOMY

Overview

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Tarsus

Tarsus

Arches of Foot

Distribution of Weight Bearing

Bony Anatomy

Musculature

Compartments

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