Trapezium !
The trapezium is the wrist bone at the base of the thumb; its saddle joint with the thumb lets it swing across the palm and often wears with age.
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What it is
The wrist bone that forms the saddle-shaped base of the thumb.
What it does
One of the eight carpal bones that let the wrist bend and carry load to the forearm.
Key facts
- Joints with
- Scaphoid, trapezoid, 1st and 2nd metacarpals
- Landmarks
- Tubercle, groove for FCR; saddle joint with the thumb metacarpal
Relations
- Above
- Scaphoid at the STT joint
- Below
- Base of the 1st metacarpal (saddle joint, held by the CMC ligaments) and the side of the 2nd metacarpal base
- Medial
- Trapezoid
- In front
- Ridge with the flexor retinaculum; origins of the abductor pollicis brevis, opponens pollicis and flexor pollicis brevis; the flexor carpi radialis tendon in its groove
- Behind
- Radial artery on the floor of the distal snuffbox; the APL tendon to the base of the 1st metacarpal nearby
How to find it
Felt at the base of the thumb, at the distal end of the anatomical snuffbox, just proximal to the base of the 1st metacarpal; circling the thumb shows where the joint line is. The palmar ridge lies deep in the thenar eminence.
Examination
- Grind test: pressing the 1st metacarpal into the trapezium and rotating it reproduces pain and crepitus in thumb-base arthritis
On imaging
A true AP of the thumb with the hand fully pronated (Robert view) and a true lateral show the saddle joint; arthritis is staged by joint narrowing, osteophytes, subluxation and involvement of the STT joint (Eaton–Littler). Ridge fractures are best seen on a carpal tunnel view or CT.
Clinical notes
- Trapeziectomy, with or without ligament reconstruction, is a common operation for advanced thumb-base arthritis
- Fractures of the body often come with a Bennett fracture or a CMC dislocation; ridge fractures are easily missed
- Dorsoradial approaches to the thumb base pass close to the radial artery and the branches of the superficial radial nerve, which are identified and protected
Development
Ossifies around age 5–6.
Test yourself
Think of the answer, then tap the question to see it.
Which joint does the trapezium form with the thumb, and why is it clinically important?
The saddle carpometacarpal joint of the thumb, one of the most common sites of hand osteoarthritis.
Which tendon runs in the groove of the trapezium?
The flexor carpi radialis tendon, just medial to the palmar ridge that anchors the flexor retinaculum.
Which examination test reproduces thumb-base arthritis pain at the trapezium?
The grind test: pressing the 1st metacarpal into the trapezium and rotating it reproduces pain and crepitus.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- os trapezium TA2 1255
- Official Spanish (DeCS)
- Hueso trapecio
- English (TA2)
- Trapezium
- Also called
- greater multangular
Related
- APB
- Thumb base cartilage
- CMC ligaments
- Dorsal intercarpal ligament
- FPB
- Flexor tendon sheaths
- FPL tendon
- Midcarpal ligaments
Sources: Terminologia Anatomica (TA2); Anatomy, Shoulder and Upper Limb, Hand Carpal Bones.
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Representative model, for educational purposes only.
