Trapezium
Os Trapezium
location_on Distal row of carpal bones, at the base of the thumb
The trapezium is the carpal bone that articulates with the first metacarpal to form the carpometacarpal (CMC) joint of the thumb. This saddle-shaped joint is uniquely human in its range of motion and enables the opposition of the thumb, which is fundamental to human hand function. The trapezium has a prominent tubercle and groove on its palmar surface through which the flexor carpi radialis tendon passes.
Key Anatomical Features
- Saddle-shaped articular surface for the first metacarpal enables thumb opposition
- Tubercle on the palmar surface provides attachment for the flexor retinaculum
- Groove for the flexor carpi radialis tendon passes along the palmar tubercle
- Articulates with the scaphoid proximally and the first and second metacarpals distally
- Palmar surface is larger than the dorsal surface
Muscle Attachments
| Muscle | Attachment | Action |
|---|---|---|
| Opponens pollicis | Trapezium tubercle | Opposes the thumb (brings it across the palm) |
| Abductor pollicis brevis | Trapezium tubercle | Abducts the thumb perpendicular to the palm |
| Flexor pollicis brevis (superficial head) | Trapezium tubercle | Flexes the proximal phalanx of the thumb |
| Flexor retinaculum | Lateral attachment to trapezium tubercle and scaphoid | Forms the roof of the carpal tunnel |
| Adductor pollicis (oblique head, indirect) | Adjacent to trapezium on capitate and metacarpals | Adducts the thumb |
Joints and Articulations
| Joint | Type | Connects to |
|---|---|---|
| First carpometacarpal joint | Synovial saddle | First metacarpal |
| Scaphotrapezial joint | Synovial plane | Scaphoid |
| Trapeziotrapezoid joint | Synovial plane | Trapezoid |
Common Pathologies
Thumb CMC arthritis (basal joint arthritis)
The most common site of hand arthritis, particularly in postmenopausal women. Causes pain at the base of the thumb with pinching and gripping. Staged by Eaton classification.
Trapezium fracture
Uncommon carpal fracture, accounting for about 4% of carpal fractures. Usually involves the body or ridge and is associated with Bennett or Rolando fractures of the first metacarpal.
De Quervain tenosynovitis (related)
Tendinopathy of the first dorsal compartment tendons that pass over the trapezium area, causing radial-sided wrist pain.
Clinical Relevance
The grind test (axial compression with rotation of the thumb metacarpal) reproduces pain in thumb CMC arthritis. Trapeziectomy (removal of the trapezium) with or without ligament reconstruction is the gold standard surgical treatment for severe thumb CMC arthritis. The flexor carpi radialis tendon passes through a groove in the trapezium and can become inflamed (FCR tendinitis), mimicking CMC arthritis.
Development and Ossification
The trapezium ossifies from a single center appearing between ages 4 and 6. It is entirely cartilaginous at birth. The saddle shape of its first metacarpal articular surface is present from the earliest stages of ossification.
Did You Know?
- The trapezium's saddle joint with the thumb metacarpal is considered one of the key anatomical features that distinguishes human hand function
- Trapezium comes from the Greek trapezion meaning small table
- Thumb CMC arthritis is 10-15 times more common in women than men
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