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 facts

Joints with: Metacarpal head (MCP joint), next phalanx (IP joint)
Landmarks: Base, shaft, head (condyles)

Relations

Above: Head of the 2nd metacarpal at the MCP joint
In front: FDS and FDP tendons in their sheath under the A2 pulley
Behind: Extensor mechanism with the extensor digitorum and 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 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

Sources: Terminologia Anatomica (TA2); Anatomy, Shoulder and Upper Limb, Hand Bones; 8.2 Bones of the Upper Limb (OpenStax (Rice University), 2022) · adapted, CC BY 4.0; 8.5 Development of the Appendicular Skeleton (OpenStax (Rice University), 2022) · adapted, CC 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.

Proximal phalanx, index finger highlighted on the Durgical 3D model