MRI Anatomy Flashcards · MSK

Hand Anatomy

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

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Hand anatomy, structure by structure

Hand and finger MRI is high-resolution, small-field work, and reading it starts with knowing the normal bones, joints, and tendons cold. This reference walks through every structure in our hand flashcard deck across the two planes it uses (sagittal and axial), with a plain-language definition, how each structure looks on MRI, and the pathology you will actually run into at the scanner.

Phalanges and metacarpals

The bony skeleton of the hand: five metacarpals in the palm and three phalanges per finger. On sagittal you follow a single ray tip to wrist; on axial you count the metacarpals across the palm.

Metacarpal

One of the five long bones of the palm that connect the wrist to the fingers, each with a base, shaft, and head.

On MRI: Seen along the proximal half of a sagittal finger image, between the carpometacarpal joint at the wrist and the metacarpophalangeal joint at the knuckle. Fatty marrow is bright on T1 and darker on fat-suppressed sequences, with a thin dark cortex.

Common pathology: Boxer fracture of the metacarpal neck (most often the fifth), stress fractures, and marrow-replacing lesions show as cortical breaks or abnormal marrow signal.

Proximal Phalanx

The first and longest of the three finger bones, articulating with the metacarpal head at the knuckle.

On MRI: Lies just beyond the metacarpophalangeal joint on a sagittal finger image; bright fatty marrow with a thin dark cortical rim, flexor tendons running along its palmar side.

Common pathology: Fractures, volar plate avulsions at its base, and marrow edema from osteomyelitis or enchondroma.

Middle Phalanx

The middle of the three finger bones, sitting between the proximal and distal phalanges (absent in the thumb).

On MRI: Found between the proximal interphalangeal joint and the distal interphalangeal joint on sagittal; same bright marrow and thin cortex as its neighbors.

Common pathology: Fractures, the central-slip insertion site for boutonniere injury, and marrow signal change from infection.

Distal Phalanx

The terminal finger bone that supports the fingertip and nail bed.

On MRI: The most distal bone on a sagittal finger image, beyond the distal interphalangeal joint; small, with a tufted tip.

Common pathology: Tuft fractures, mallet-finger avulsion at the extensor insertion, and glomus tumors of the nail bed.

Tip: On a sagittal ray, count bones from the tip: distal, then middle, then proximal phalanx, then the metacarpal.

First Metacarpal

The metacarpal of the thumb, the shortest and most mobile, set apart from the others toward the radial (lateral) side.

On MRI: The most lateral and isolated metacarpal on an axial slice through the palm, separated from the second by a wide soft-tissue gap.

Common pathology: Bennett and Rolando fractures at its base, and basal thumb (first carpometacarpal) osteoarthritis.

Second Metacarpal

The metacarpal of the index finger, one of the longest of the five (the second and third metacarpals are the longest, with the third usually slightly longer).

On MRI: The next metacarpal medial to the thumb on an axial palm image; round cortical ring with bright central marrow.

Common pathology: Fractures and the most common site of metacarpal stress injury in athletes.

Third Metacarpal

The metacarpal of the middle finger, central in the palm.

On MRI: The middle of the five metacarpal cross-sections on an axial slice, aligned with the central axis of the hand.

Common pathology: Fractures and the styloid base avulsion at the extensor carpi radialis brevis insertion.

Fourth Metacarpal

The metacarpal of the ring finger.

On MRI: The fourth cross-section moving toward the ulnar (medial) side on an axial palm image.

Common pathology: Neck and shaft fractures, often grouped with fifth-metacarpal injuries.

Fifth Metacarpal

The metacarpal of the little finger, on the ulnar (medial) edge of the palm.

On MRI: The most medial metacarpal cross-section on an axial slice, at the ulnar border of the hand.

Common pathology: Boxer fracture of the neck is the classic injury; base fractures involve the hamate articulation.

Sesamoid Bones

Small bones embedded within tendons, most consistently a pair on the palmar side of the thumb metacarpophalangeal joint.

On MRI: Tiny rounded ossicles with marrow signal sitting in the flexor tendons on the palmar aspect of the thumb on axial images.

Common pathology: Sesamoiditis, fracture, and osteonecrosis; distinguishing a bipartite sesamoid from a fracture is a common question.

Joints

The chain of joints from palm to fingertip. Sagittal is the workhorse plane: it lines up the carpometacarpal, metacarpophalangeal, and interphalangeal joints of a single ray in one image.

Carpometacarpal (CMC) Joint

The joint between the carpal (wrist) bones and the base of a metacarpal, at the proximal end of each ray.

On MRI: The most proximal joint on a sagittal finger image, where the metacarpal base meets the carpal row; the thumb (first) CMC is the most mobile and clinically important.

Common pathology: Basal thumb osteoarthritis at the first CMC is extremely common; look for joint-space narrowing, subchondral cysts, and marrow edema.

Metacarpophalangeal (MCP) Joint

The knuckle joint between a metacarpal head and the base of the proximal phalanx.

On MRI: The joint at the knuckle on a sagittal ray, between the metacarpal and proximal phalanx; the volar plate and collateral ligaments bracket it.

Common pathology: Thumb ulnar collateral ligament tear (skier or gamekeeper thumb), volar plate injury, and early erosive change in inflammatory arthritis.

Proximal Interphalangeal (PIP) Joint

The middle finger joint between the proximal and middle phalanges.

On MRI: The next joint distal to the knuckle on a sagittal finger image, between the proximal and middle phalanges.

Common pathology: Volar plate avulsion, central-slip injury leading to boutonniere deformity, and osteoarthritis (Bouchard nodes).

Distal Interphalangeal (DIP) Joint

The fingertip joint between the middle and distal phalanges (the thumb has only one interphalangeal joint).

On MRI: The most distal joint on a sagittal ray, just behind the fingertip, between the middle and distal phalanges.

Common pathology: Mallet finger from extensor avulsion, osteoarthritis (Heberden nodes), and psoriatic arthritis (a classic DIP target).

Tendons and tunnel

The flexor tendons run along the palmar side and the extensors along the dorsal side. Sagittal traces a tendon along the finger; axial is best for sorting tendon cross-sections and the carpal tunnel.

Flexor Tendon

The tendon group on the palmar side of the finger that bends (flexes) the digit toward the palm.

On MRI: A dark band running along the palmar surface of the phalanges on a sagittal finger image, low signal on all standard sequences within its sheath.

Common pathology: Flexor tendon tears, trigger finger (stenosing tenosynovitis at the A1 pulley), and tenosynovitis with bright fluid in the sheath.

Extensor Tendon

The tendon on the dorsal side of the finger that straightens (extends) the digit.

On MRI: A thin dark band along the dorsal surface of the phalanges on a sagittal finger image, thinning into the extensor hood over the joints.

Common pathology: Mallet finger (distal avulsion), central-slip rupture (boutonniere), and sagittal-band injury causing extensor tendon subluxation at the knuckle.

Extensor Digitorum Tendon

The tendon of the extensor digitorum muscle that extends the four fingers, lying on the dorsum of the hand.

On MRI: Round to oval dark tendon cross-sections lined up along the dorsal (back) surface of the metacarpals on an axial palm image.

Common pathology: Extensor tenosynovitis, lacerations from dorsal hand wounds, and subluxation at the metacarpophalangeal level.

Flexor Digitorum Profundus Tendon

The deep finger flexor tendon that flexes the distal interphalangeal joint, inserting on the distal phalanx.

On MRI: A dark tendon cross-section on the palmar side, lying deep (dorsal) to the superficialis tendon within the same flexor sheath on axial images.

Common pathology: Jersey finger (avulsion of the FDP insertion on the distal phalanx) and tenosynovitis.

Tip: In the flexor sheath the deep profundus sits behind the superficialis; closer to the bone is profundus.

Flexor Digitorum Superficialis Tendon

The superficial finger flexor tendon that flexes the proximal interphalangeal joint, splitting to insert on the middle phalanx.

On MRI: A dark tendon cross-section lying superficial (palmar) to the profundus tendon within the flexor sheath on axial images.

Common pathology: Tendon laceration, tenosynovitis, and entrapment within the fibro-osseous tunnel.

Carpal Tunnel

The fibro-osseous passage at the wrist, roofed by the flexor retinaculum, that carries the flexor tendons and the median nerve into the hand.

On MRI: Shown on the sagittal hand image as the flexor tendons coursing deep to the flexor retinaculum, which forms the roof of the tunnel; the tunnel and its contents (the flexor tendons and the median nerve) are characterized in cross-section on axial images.

Common pathology: Carpal tunnel syndrome with median nerve swelling proximally and flattening within the tunnel (assessed on axial images), ganglion cysts, and tenosynovial thickening narrowing the tunnel.

Frequently asked questions

What structures are seen on a hand MRI?

A hand MRI shows the bony skeleton (the five metacarpals and the proximal, middle, and distal phalanges, plus the thumb sesamoids), the joints of each ray (carpometacarpal, metacarpophalangeal, proximal interphalangeal, and distal interphalangeal), and the soft tissues, including the flexor and extensor tendons and the carpal tunnel. This page labels every structure in the deck with its MRI appearance.

Which planes are used for hand and finger MRI?

Sagittal and axial are the core planes in this deck. Sagittal lines up a single finger ray so you can follow the metacarpal, phalanges, joints, and tendons end to end, while axial is best for counting the metacarpals across the palm and sorting the flexor and extensor tendon cross-sections. A coronal is often added clinically to compare the rays side by side.

How do you tell the flexor digitorum profundus from the superficialis tendon?

On an axial image through the finger both tendons sit in the same flexor sheath on the palmar side. The superficialis lies superficial (closer to the palm) and the profundus lies deep (closer to the bone). The profundus continues to the distal phalanx, while the superficialis splits to insert on the middle phalanx.

What sequences are typical for hand and finger MRI?

Hand imaging uses a small field of view with high in-plane resolution. T1-weighted images show marrow and anatomy well, fluid-sensitive fat-suppressed sequences (such as STIR or fat-suppressed T2 or proton density) highlight marrow edema, tenosynovitis, and soft-tissue fluid, and contrast is added when infection, inflammatory arthritis, or a mass is suspected. Tendons and cortex stay dark on all standard sequences.

Do I need an account to use these hand 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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