3rd metacarpal !
The third metacarpal is the palm bone of the middle finger; it forms the stable centre of the palm and anchors a main wrist extensor.
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What it is
The long bone in the palm leading to the middle finger.
What it does
Forms the palm and the knuckle at its head.
Key facts
- Joints with
- Base: capitate; head: proximal phalanx; adjacent metacarpals
- Landmarks
- Base, shaft, neck, head (knuckle)
Relations
- Above
- Capitate
- Behind
- ECRB on the styloid process; extensor digitorum tendon to the middle finger
- In front
- Transverse and oblique heads of the adductor pollicis; the deep palmar arch near its base
- Lateral
- Second dorsal interosseous
- Medial
- Third dorsal interosseous
- Below
- Proximal phalanx of the middle finger
How to find it
The styloid process is felt as a small bump at the base of the 3rd metacarpal on the back of the hand, just distal to the capitate, more obvious with the wrist flexed; the head is the most prominent knuckle of a fist.
On imaging
Seen on PA, oblique and lateral hand views. The styloid process sits on the dorsal radial corner of its base; a separate small bone there (os styloideum) or a bony bump (carpal boss) is best shown on a lateral view and should not be read as a fracture. CT clarifies complex CMC injuries; ultrasound shows a ganglion over a carpal boss.
Clinical notes
- A prominent styloid or an osteophyte here forms the carpal boss, which can be confused with a dorsal wrist ganglion
- Shaft fractures of this central metacarpal shorten little, because the deep transverse metacarpal ligaments tie its head to the neighbouring heads on both sides
- Fracture-dislocations at its carpometacarpal joint are rare and need high energy, since the joint with the capitate is locked by strong ligaments
Anatomical variants
- Os styloideum: an accessory ossicle at the base, in place of a fused styloid process
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 is easy to mistake for a fracture.
Related conditions
Test yourself
Think of the answer, then tap the question to see it.
Which metacarpal has a styloid process, and what inserts on it?
The 3rd metacarpal; the extensor carpi radialis brevis inserts on its styloid process.
Why are finger abduction and adduction described relative to the 3rd metacarpal and middle finger?
The axis of the hand passes through the middle finger.
What forms a carpal boss at the 3rd metacarpal base?
A prominent styloid process or an osteophyte, which can be confused with a dorsal wrist ganglion.
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 III
- English (TA2)
- 3rd metacarpal
Related
- A1 pulleys
- Adductor pollicis
- CMC ligaments
- Dorsal interossei
- ECRB
- Extensor tendons
- Finger joint capsules
- Lumbricals
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.
