MRI Anatomy Flashcards · MSK

Foot Anatomy

Learn to identify every labeled structure on a Foot MRI, plane by plane.

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Foot anatomy, structure by structure

Foot MRI is a high-volume musculoskeletal study, and reading it cleanly starts with knowing which bone you are looking at on a small, busy field of view. This reference walks through every structure in our foot flashcard deck across the two scan planes used here (axial, the long axis of the foot, and coronal, the short axis), with a plain-language definition, how each structure looks on MRI, and the pathology you will actually run into at the scanner.

Forefoot bones

The metatarsals and toe phalanges that make up the front of the foot. On the axial (long axis) plane you read the rays out toward the toes; on the coronal (short axis) plane you compare the metatarsals side by side.

First Metatarsal

The long bone of the great-toe ray, the shortest and thickest of the five metatarsals, running from the medial cuneiform to the base of the great toe.

On MRI: On the axial (long axis) plane it is the most medial metatarsal, seen end to end as a long bone with bright fatty marrow on T1; on the coronal (short axis) plane it is the largest metatarsal cross-section, sitting medial and slightly plantar to the others.

Common pathology: Stress reaction, first-ray osteoarthritis, and gout at the first metatarsophalangeal joint.

Second Metatarsal

The longest metatarsal, forming the second ray and recessed at its base into the cuneiforms, which makes it the most rigidly fixed.

On MRI: Lies just lateral to the first metatarsal and is the longest metatarsal, so on the axial (long axis) plane it projects furthest toward the toes in the normal length cascade. Bright fatty marrow on T1, intermediate on T2.

Common pathology: A classic site for metatarsal stress (march) fractures and for Freiberg infraction at the head.

Third Metatarsal

The central metatarsal of the third ray, sitting between the second and fourth metatarsals.

On MRI: Tracked between the second and fourth rays on the axial (long axis) plane; on the coronal (short axis) plane it is the middle of the five metatarsal cross-sections.

Common pathology: Stress fractures and, at the second/third interspace, Morton neuroma involving the plantar digital nerve.

Fourth Metatarsal

The metatarsal of the fourth ray, lying between the third and fifth metatarsals and articulating proximally with the cuboid.

On MRI: Seen lateral to the third metatarsal; on the coronal (short axis) plane its base abuts the cuboid rather than a cuneiform. Normal fatty marrow signal.

Common pathology: Stress fractures and adjacent third/fourth interspace Morton neuroma.

Fifth Metatarsal

The most lateral metatarsal, forming the fifth ray, with a prominent tuberosity at its base on the lateral border of the foot.

On MRI: The most lateral metatarsal on both planes; its flared base and styloid tuberosity are the easiest lateral forefoot landmark. Fatty marrow on T1.

Common pathology: Avulsion fractures of the tuberosity and Jones fractures at the metaphyseal-diaphyseal junction.

Tip: On the lateral edge of the foot, follow the bone with the flared, beak-like base out toward the little toe; that is the fifth metatarsal.

Head of Fifth Metatarsal

The rounded distal end of the fifth metatarsal that articulates with the proximal phalanx of the little toe.

On MRI: The lateral-most, distal-most metatarsal head on the axial (long axis) plane, capped by a thin dark line of articular cartilage facing the small toe.

Common pathology: Bunionette (tailor bunion) deformity and lateral metatarsophalangeal joint degeneration.

Base of Fifth Metatarsal

The proximal, flared end of the fifth metatarsal, including the styloid tuberosity where the fibularis brevis tendon attaches.

On MRI: A broad, beak-shaped proximal segment on the lateral foot, projecting toward the cuboid; the tuberosity points proximally and laterally.

Common pathology: One of the most common avulsion-fracture sites in the foot, plus the closely related Jones fracture just distal to it.

Tip: This is the lateral bony bump patients land on with an inversion injury; check carefully for an avulsion fragment here.

Proximal Phalanx Great Toe

The base bone of the great toe (hallux), articulating with the first metatarsal head at the first metatarsophalangeal joint.

On MRI: The large, single proximal phalanx of the medial-most ray on the axial (long axis) plane; the great toe has only two phalanges, so this is its more proximal segment.

Common pathology: First metatarsophalangeal joint arthritis, gout, and sesamoid-related pain referred from beneath this joint.

First Distal Phalanx

The distal (tip) bone of the great toe, the terminal segment of the hallux.

On MRI: The small distal bone at the very tip of the medial-most ray on the axial (long axis) plane, distal to the proximal phalanx of the great toe.

Common pathology: Subungual lesions, osteomyelitis spreading from a nail-bed or tip infection, and tuft injuries.

Proximal Phalanx

The base bone of a lesser toe (toes two through five), articulating with its metatarsal head.

On MRI: The most proximal of the three small toe bones in a lesser ray on the axial (long axis) plane, lined up just distal to the metatarsal head.

Common pathology: Osteomyelitis (especially in diabetic forefoot infection) and stress changes.

Middle Phalanx

The central bone of a lesser toe, present in toes two through five but absent in the great toe.

On MRI: The middle of the three small bones in a lesser ray on the axial (long axis) plane, between the proximal and distal phalanges.

Common pathology: Hammer/claw-toe deformity changes and small-bone osteomyelitis in diabetic infection.

Distal Phalanx

The tip bone of a lesser toe, the terminal segment of toes two through five.

On MRI: The smallest, most distal bone at the tip of a lesser ray on the axial (long axis) plane.

Common pathology: Tip osteomyelitis, subungual pathology, and traumatic tuft fractures.

Midfoot

The tarsal bones that bridge the forefoot and hindfoot. They are best confirmed on the axial (long axis) plane where their wedge shapes and articulations line up.

Medial Cuneiform Bone

The largest of the three cuneiform bones, sitting on the medial midfoot between the navicular and the base of the first metatarsal.

On MRI: A wedge-shaped tarsal bone medially on the axial (long axis) plane, articulating distally with the first metatarsal; bright fatty marrow on T1.

Common pathology: Midfoot (Lisfranc) injury and osteoarthritis at the first tarsometatarsal joint.

Cuboid Bone

The cube-shaped tarsal bone on the lateral midfoot, articulating with the calcaneus behind and the fourth and fifth metatarsals in front.

On MRI: A roughly square tarsal bone on the lateral side on the axial (long axis) plane, sitting proximal to the fourth and fifth metatarsal bases; a groove on its plantar surface carries the fibularis longus tendon.

Common pathology: Cuboid stress fractures, cuboid syndrome, and lateral-column involvement in Lisfranc injury.

Plantar soft tissue and sesamoids

The supporting soft tissue and the two small bones under the great toe. The sesamoids and the plantar fascia stand out best on the coronal (short axis) plane.

Plantar Aponeurosis

The thick fibrous band (plantar fascia) running along the sole from the calcaneus to the forefoot that supports the longitudinal arch.

On MRI: A thin, uniformly dark (low signal) band hugging the plantar surface of the foot on the coronal (short axis) plane, just superficial to the plantar fat pad.

Common pathology: Plantar fasciitis (thickening with edema near the calcaneal origin), plantar fibromatosis, and fascial tears.

Tip: It is the dark fibrous sheet right under the skin and fat on the bottom of the foot; normal fascia stays thin and uniformly low signal.

Medial Sesamoid Bone

The medial (tibial) of the two small bones embedded in the flexor hallucis brevis tendon beneath the first metatarsal head.

On MRI: A small ovoid bone on the medial side of the plantar first metatarsal head on the coronal (short axis) plane, with fatty marrow on T1; it can be bipartite normally.

Common pathology: Sesamoiditis, stress fracture, avascular necrosis, and turf-toe complex injuries.

Tip: Of the two bones under the big-toe joint, the one toward the inside (great-toe side) of the foot is the medial sesamoid.

Lateral Sesamoid Bone

The lateral (fibular) of the two small bones embedded in the flexor hallucis brevis tendon beneath the first metatarsal head.

On MRI: A small ovoid bone lateral to the medial sesamoid under the plantar first metatarsal head on the coronal (short axis) plane, sharing fatty marrow signal.

Common pathology: Sesamoiditis, stress fracture, and disruption as part of turf-toe injury.

Frequently asked questions

What structures are seen on a foot MRI?

A forefoot and midfoot MRI shows the five metatarsals (with the head and base of the fifth highlighted separately), the toe phalanges (proximal, middle, and distal, plus the great-toe proximal and distal phalanges), the medial cuneiform and cuboid in the midfoot, the medial and lateral sesamoids beneath the first metatarsal head, and the plantar aponeurosis (fascia). This page labels each one with its MRI appearance.

Which planes are used for foot MRI anatomy?

This deck uses two planes named for the foot itself: the axial plane runs along the long axis of the foot and is best for reading the metatarsals and phalanges out toward the toes, while the coronal plane is the short axis (a cross-section through the forefoot) and is best for the sesamoids and the plantar fascia. Many clinical foot protocols add a third, sagittal plane as well.

How do you tell the fifth metatarsal base from a Jones fracture region?

The base of the fifth metatarsal is the flared, beak-shaped proximal end with the styloid tuberosity where the fibularis brevis attaches; it is a common avulsion-fracture site after an inversion injury. The Jones fracture sits just distal to it at the metaphyseal-diaphyseal junction. Knowing the exact base landmark helps you center coverage and spot small avulsion fragments.

What sequences best show the plantar fascia and sesamoids?

Fluid-sensitive sequences (T2 or PD with fat saturation, or STIR) make marrow edema in the sesamoids and inflammation around the plantar fascia stand out as bright signal, while T1 shows the normal fatty marrow and the thin dark plantar aponeurosis. Reading them together separates a normal bipartite sesamoid or thin fascia from sesamoiditis, a stress fracture, or plantar fasciitis.

Do I need an account to use these Foot MRI flashcards?

No. The interactive flashcards and this full labeled reference are open to use, with no account required to start. Creating an account lets you save your progress across devices and track which packs you have mastered.

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