Proximal phalanx of index finger: anatomy, location and function

What it is

The longest of the three phalanges of the index finger (second digit), nearest the palm.

Location

Its base articulates with the head of the metacarpal at the metacarpophalangeal joint; its head articulates with the middle phalanx at the proximal interphalangeal joint.

Function

Forms the base of the finger and allows flexion, extension, abduction and adduction at the knuckle.

Body system

Skeletal · paired (left and right)

FMA ID

FMA71915 (Foundational Model of Anatomy)

Key facts

• The first dorsal interosseous inserts on the radial side of its base and the first palmar interosseous on the ulnar side, mainly through the extensor expansion.
• Its head forms the proximal interphalangeal joint, a hinge joint stabilised by collateral ligaments and the palmar plate.
• The extensor expansion (dorsal hood) wraps around it, receiving the lumbrical on its radial side.

Clinical relevance

Fractures of the proximal phalanx usually angulate with the apex toward the palm because of the pull of the interossei and extensor hood; rotation must be corrected so the index finger does not cross its neighbours when making a fist.

The nearest named structures in the 3D model, measured from the centre of each part:

• Proximal phalanx of middle finger · skeletal
• Middle phalanx of index finger · skeletal
• Lumbricals of hand · muscular
• Distal phalanx of thumb · skeletal
• Middle phalanx of middle finger · skeletal
• Proximal phalanx of ring finger · skeletal
• Proximal phalanx of thumb · skeletal
• Distal phalanx of index finger · skeletal
• Palmar interossei of hand · muscular
• Second metacarpal bone · skeletal