5th metacarpal !
The fifth metacarpal is the palm bone of the little finger; its neck breaks in a punch, the classic boxer's fracture.
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What it is
The long bone in the palm leading to the little finger.
What it does
Forms the palm and the knuckle at its head.
Key facts
- Joints with
- Base: hamate; head: proximal phalanx; adjacent metacarpals
- Landmarks
- Base, shaft, neck, head (knuckle); neck = boxer's fracture
Relations
- Above
- Hamate at the base
- Behind
- ECU insertion on the back of the base; extensor digiti minimi tendon; the dorsal branch of the ulnar nerve crosses near the base
- In front
- Opponens digiti minimi along the shaft; the flexor carpi ulnaris reaches the base through the pisometacarpal ligament
- Lateral
- Fourth dorsal interosseous and third palmar interosseous
- Medial
- Subcutaneous ulnar border; abductor digiti minimi passes alongside to the little finger
- Below
- Proximal phalanx of the little finger
How to find it
The ulnar border is subcutaneous from the base, just distal to the hamate with the ECU tendon, to the knuckle; the neck lies just behind the knuckle.
On imaging
PA, lateral and oblique views; the lateral shows how far the head is tilted. A reverse Bennett fracture is best seen on a pronated oblique view or CT.
Common problems
- Boxer's fracture of the neck, from punching a hard object.
- Rotation of the broken bone can make the little finger cross over the ring finger when making a fist.
How it is diagnosed
Exam of the knuckle and of finger rotation in a fist. X-rays show the angle.
Treatment
- Splint or cast with early motion for most fractures.
- Pins or a plate when the finger is rotated or the angle is large.
Clinical notes
- Rotation is judged with the fingers flexed: the nails normally point toward the scaphoid tubercle, and a rotated fracture makes the little finger cross under the ring finger
- Base fractures can be accompanied by injury of the dorsal branch of the ulnar nerve
Development
Ossifies in cartilage: a primary centre appears in the shaft before birth and one secondary centre later forms at the head, not at the base as in the 1st metacarpal. On a child's X-ray the open plate near the head shows as a dark line that should not be confused with a boxer's fracture.
Related conditions
Test yourself
Think of the answer, then tap the question to see it.
What is a boxer's fracture of the 5th metacarpal?
A neck fracture in which the head tips toward the palm (apex dorsal), from punching a hard object.
Why does the 5th metacarpal tolerate the most angulation of all metacarpals?
Its carpometacarpal joint with the hamate is the most mobile.
How is a wound over the 5th knuckle after a punch treated?
As a human bite (fight bite) that may have entered the MCP joint.
How is rotation of a 5th metacarpal fracture judged?
With the fingers flexed: the nails normally point to the scaphoid tubercle; a rotated fracture makes the little finger cross under the ring finger.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- ossa metacarpi TA2 1264
- Official Spanish (DeCS)
- Hueso metacarpiano V
- English (TA2)
- 5th metacarpal
Related
- A1 pulleys
- Abductor digiti minimi
- CMC ligaments
- Dorsal interossei
- ECU
- Extensor tendons
- FCU tendon
- Finger joint capsules
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.
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Representative model, for educational purposes only.
