1st metacarpal !
The first metacarpal is the palm bone of the thumb, from the wrist to the thumb knuckle; its short, mobile base lets the thumb oppose.
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What it is
The long bone in the palm leading to the thumb.
What it does
Forms the palm and the knuckle at its head.
Key facts
- Joints with
- Base: trapezium (saddle joint); head: proximal phalanx
- Landmarks
- Base, shaft, neck, head (knuckle)
Relations
- Above
- Trapezium at the saddle joint, held by the CMC ligaments, including the anterior oblique (beak) ligament
- Behind
- APL tendon on the radial side of the base; the EPB and EPL tendons run down the back of the shaft
- In front
- Opponens pollicis along the radial side of the shaft; the FPL tendon passes in front on its way to the thumb
- Medial
- First web space with the adductor pollicis and the first dorsal interosseous (one head arises from it); the radial artery passes between it and the 2nd metacarpal into the palm
- Below
- Proximal phalanx of the thumb at the MCP joint, with the thumb sesamoids and the thumb UCL
How to find it
Followed along the back of the thumb from the base, just distal to the anatomical snuffbox, to the head at the thumb knuckle; circling the thumb shows the carpometacarpal joint line.
On imaging
A true AP of the thumb (hand fully pronated) and a true lateral: a Bennett fracture shows a small fragment at the ulnar base with the shaft displaced; a Rolando fracture shows several fragments.
Clinical notes
- Bennett and Rolando fractures are unstable because of the pull of the APL and adductor pollicis and usually need reduction and fixation to protect the joint
- Extra-articular base fractures tolerate more angulation than other metacarpal fractures, thanks to the mobile saddle joint
Development
Unlike the other metacarpals, its secondary ossification centre is at the base, as in a phalanx.
Related conditions
Test yourself
Think of the answer, then tap the question to see it.
What is a Bennett fracture of the 1st metacarpal?
A two-part intra-articular base fracture: a palmar-ulnar fragment stays held by the beak ligament while the abductor pollicis longus pulls the shaft away.
How does a Rolando fracture of the 1st metacarpal differ from a Bennett fracture?
It is a comminuted (Y- or T-shaped) intra-articular base fracture, with a worse outlook.
Where is the secondary ossification centre of the 1st metacarpal?
At the base, as in a phalanx, unlike the other metacarpals.
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 I
- English (TA2)
- 1st metacarpal
Related
- A1 pulleys
- APB
- Adductor pollicis
- APL
- APL and EPB tendons
- Thumb base cartilage
- CMC ligaments
- Dorsal interossei
Sources: Terminologia Anatomica (TA2); Anatomy, Shoulder and Upper Limb, Hand Bones.
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Representative model, for educational purposes only.
