Distal phalanx, thumb !

The distal phalanx of the thumb is the bone of the thumb tip; the long thumb flexor and extensor attach to its base.

Official name: Distal phalanx of the thumb

See in 3D →

Opens in the Durgical app, no sign-up needed.

What it is

The distal bone of the thumb. It carries the nail and the fingertip pad.

What it does

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

Key facts

Joints with: Proximal phalanx (thumb IP)
Landmarks: Base (FDP/FPL insertion, terminal extensor), tuberosity under the nail

Relations

Above: Head of the proximal phalanx of the thumb at the IP joint, with its volar plate
In front: FPL tendon to the base; the fingertip pulp with the digital nerves
Behind: EPL tendon to the base; the nail bed and nail plate over the tuft

How to find it

Under the thumbnail and pulp. The FPL pull on its palmar base is checked by holding the proximal phalanx and asking for the tip of the thumb to bend.

Examination

OK sign: asked to make a ring with the thumb and index, the person pinches with flat pads instead of tips when the anterior interosseous nerve (FPL and index FDP) is affected

On imaging

True AP and lateral views of the thumb. Crush injuries give a comminuted tuft fracture. A small fragment pulled from the dorsal base means an EPL avulsion (mallet thumb); one from the palmar base means an FPL avulsion. When no fragment is seen and the IP joint cannot be flexed, ultrasound finds the retracted FPL tendon end.

Clinical notes

Tuft fractures from crush injuries often come with a nail bed laceration or a painful subungual haematoma
Mallet thumb: the EPL tendon tears or pulls a fragment off its dorsal base and the IP joint droops; it is less common than mallet finger
Pulp infection (felon) of the thumb can spread to the bone if the pressure in the pulp compartments is not relieved

Development

Ossifies from a primary centre that starts at the tip early in fetal life and one secondary centre at its base, which fuses in adolescence.

Test yourself

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

Which tendons insert on the distal phalanx of the thumb?

The flexor pollicis longus on the palmar base and the extensor pollicis longus on the dorsal base.

Loss of active flexion of the thumb IP joint suggests which lesions?

A cut flexor pollicis longus or an anterior interosseous nerve palsy.

What is the OK sign?

In anterior interosseous nerve palsy the person pinches with flat pads instead of tips when asked to make a ring with thumb and index.

Add to my cards (3)

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

Its names

Official Latin (TA2): phalanx distalis manus TA2 1279
Official Spanish (DeCS): Falange distal del pulgar
English (TA2): Distal phalanx of the thumb

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

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.