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# Proximal phalanx, index finger

The proximal phalanx of the index finger is its first bone beyond the knuckle; the small hand muscles that spread the finger attach to it.

Official name: Proximal phalanx of the index finger

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## What it is

The proximal bone of the index finger.

## What it does

One of the finger bones; the joints between them let the finger curl.

## Key points

- The first dorsal interosseous inserts on its radial base and the first palmar interosseous on its ulnar side, so it carries the pull for index abduction and adduction in pinch
- Proximal phalanx shaft fractures tend to angulate apex palmar: the interossei flex the base fragment while the central slip extends the distal one

## Key facts

**Joints with**
Metacarpal head (MCP joint), next phalanx (IP joint)

**Landmarks**
Base, shaft, head (condyles)

## Relations

**Above**
Head of the [2nd metacarpal](https://durgical.com/en/anatomy/2nd-metacarpal/) at the MCP joint

**In front**
FDS and [FDP tendons](https://durgical.com/en/anatomy/flexor-digitorum-profundus-tendons/) in their sheath under the A2 pulley

**Behind**
Extensor mechanism with the [extensor digitorum](https://durgical.com/en/anatomy/extensor-digitorum/) and [extensor indicis](https://durgical.com/en/anatomy/extensor-indicis/) tendons

**Lateral**
First dorsal interosseous and the first lumbrical joining the extensor hood

## How to find it

Run a finger along the back of the index from the second knuckle to the first finger joint: that bony segment is its shaft. On the palm, the crease at the base of the finger lies over the proximal half of this bone, not over the MCP joint.

## Examination

- Finger cascade: with the fingers half-bent, each nail should point toward the [scaphoid](https://durgical.com/en/anatomy/scaphoid/) tubercle; an index that crosses toward the middle finger points to a rotated fracture

## On imaging

Posteroanterior, oblique and true lateral views of the index finger, centred on the bone; the lateral view shows apex-palmar angulation, while rotation is judged at the bedside rather than on film.

## Clinical notes

- Rotational malunion makes the index overlap the middle finger when a fist is made
- The shaft sits right under the flexor tendons in the A2 pulley, so scarring after a fracture or fixation often limits active finger bending

## Development

Ossifies from a primary centre in the shaft before birth and a single secondary centre at its base, whose growth plate closes in adolescence.

## Test yourself

Think of the answer, then tap the question to see it.

## Which interossei insert on the proximal phalanx of the index finger?

The first dorsal interosseous on the radial base and the first palmar interosseous on the ulnar side.

## Why do proximal phalanx shaft fractures of the index finger angulate apex palmar?

The interossei flex the base fragment while the central slip extends the distal fragment.

## What does rotational malunion of the proximal phalanx of the index finger cause?

The index overlaps the middle finger when a fist is made.

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Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
phalanx proximalis manus TA2 1277

**Official Spanish (DeCS)**
Falange proximal del índice

**English (TA2)**
Proximal phalanx of the index finger

## Related

- [Digital arteries](https://durgical.com/en/anatomy/palmar-digital-arteries/)
- [A1 pulleys](https://durgical.com/en/anatomy/a1-pulleys-of-the-flexor-tendon-sheaths/)
- [Extensor tendons](https://durgical.com/en/anatomy/extensor-digitorum-tendons/)
- [FDP tendons](https://durgical.com/en/anatomy/flexor-digitorum-profundus-tendons/)
- [Finger joint capsules](https://durgical.com/en/anatomy/finger-joint-capsules/)
- [Finger pulleys](https://durgical.com/en/anatomy/flexor-tendon-sheaths-and-pulleys/)
- [Flexor tendon sheaths](https://durgical.com/en/anatomy/flexor-tendon-synovial-sheaths/)
- [Finger collateral ligaments](https://durgical.com/en/anatomy/collateral-ligaments-of-the-finger-joints/)

Sources: Terminologia Anatomica (TA2); [Anatomy, Shoulder and Upper Limb, Hand Bones](https://www.ncbi.nlm.nih.gov/books/NBK547684/); [8.2 Bones of the Upper Limb](https://openstax.org/books/anatomy-and-physiology-2e/pages/8-2-bones-of-the-upper-limb) (OpenStax (Rice University), 2022) · adapted, [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); [8.5 Development of the Appendicular Skeleton](https://openstax.org/books/anatomy-and-physiology-2e/pages/8-5-development-of-the-appendicular-skeleton) (OpenStax (Rice University), 2022) · adapted, [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); Anatomy of the Human Body (20th ed.): Articulations of the Digits (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain.

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/anatomy/proximal-phalanx-of-the-index-finger/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/proximal-phalanx-of-the-index-finger/