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# Middle phalanx, index finger

The middle phalanx of the index finger is its middle bone, between the two finger joints; tendons that bend and straighten the finger attach here.

Official name: Middle phalanx of the index finger

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## What it is

The middle bone of the index finger.

## What it does

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

## Key points

- The two slips of FDS insert on the sides of its shaft and the central slip of the extensor on its dorsal base
- A volar plate avulsion fragment at its palmar base follows PIP hyperextension; a large fragment can let the joint sublux dorsally

## Key facts

**Joints with**
Proximal phalanx (PIP), distal phalanx (DIP)

**Landmarks**
Base, shaft, head; FDS inserts on its sides

## Relations

**Above**
Head of the proximal phalanx at the PIP joint, with the [volar plates (fingers)](https://durgical.com/en/anatomy/volar-plates-of-the-interphalangeal-joints/) and [finger collateral ligaments](https://durgical.com/en/anatomy/collateral-ligaments-of-the-finger-joints/)

**In front**
FDP tendon on its way to the distal phalanx, between the FDS slips

**Behind**
Central slip at the base; lateral bands passing on each side toward the distal phalanx

## How to find it

The short bony segment on the back of the index between the two finger joints; the middle finger crease on the palm marks the PIP joint at its base.

## Examination

- Superficialis test: with the other fingers held straight, the person bends only the index at the PIP joint; failure suggests an FDS tendon cut (the index FDS can sometimes be helped by its own FDP, so compare both sides)
- Elson test: with the PIP bent 90° over a table edge, weak middle-phalanx extension and a rigid DIP suggest a central slip rupture

## On imaging

A true lateral view of the index is the key film: it shows a palmar base fragment from the volar plate and any dorsal subluxation of the base (a gap shaped like a V on the back of the joint).

## Clinical notes

- Central slip rupture at its base leads to a boutonnière deformity (PIP flexed, DIP hyperextended)
- In a dorsal PIP fracture-dislocation, the loss of a large part of its palmar base lets the phalanx slide backward; a congruent joint on the true lateral view is the aim of treatment

## Development

Like the other phalanges, it ossifies from a shaft centre before birth and one secondary centre at its base; middle phalanges are generally the last phalanges to start ossifying.

## Test yourself

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

## Which tendons insert on the middle phalanx of the index finger?

The two slips of flexor digitorum superficialis on the sides and the extensor central slip on the dorsal base.

## What deformity follows rupture of the central slip at the base of the middle phalanx?

Boutonnière deformity: PIP flexed and DIP hyperextended.

## What injury causes a volar plate avulsion fragment at the palmar base of the middle phalanx?

Hyperextension of the PIP joint; a large fragment can let the joint sublux dorsally.

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

## Its names

**Official Latin (TA2)**
phalanx media manus TA2 1278

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

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

## Related

- [Extensor tendons](https://durgical.com/en/anatomy/extensor-digitorum-tendons/)
- [FDP](https://durgical.com/en/anatomy/flexor-digitorum-profundus/)
- [FDP tendons](https://durgical.com/en/anatomy/flexor-digitorum-profundus-tendons/)
- [FDS](https://durgical.com/en/anatomy/flexor-digitorum-superficialis/)
- [FDS tendons](https://durgical.com/en/anatomy/flexor-digitorum-superficialis-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/)

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/middle-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/middle-phalanx-of-the-index-finger/