Upper limb
Trapezium bone
Os trapezium
- Origin
- Radial bone of the distal row. Its distal surface carries a saddle shaped facet for the first metacarpal, and it meets the scaphoid proximally and the trapezoid on the ulnar side.
- Insertion
- Attachment for the flexor retinaculum on its tubercle, and for abductor pollicis brevis, opponens pollicis and flexor pollicis brevis.
- Function
- Carries the thumb base joint and so makes thumb opposition possible, the movement the human grasping hand rests on.
- Innervation
- Median nerve, recurrent branch (C6-C7)
- Movement & chain
- Barely mobile itself; all movement happens in the saddle joint above it, which allows two degrees of freedom plus a screw movement.
- Palpation
- On the thumb side, distal to the anatomical snuffbox, between the scaphoid and the base of the first metacarpal.
- Clinical
- Osteoarthritis of the thumb base joint is one of the most common hand conditions, especially in women after the menopause: pain on pinching and twisting, and in time an adducted thumb. In the groove on its palmar side the flexor carpi radialis tendon can become irritated.
- Segmental innervation
- C6-C7
- In clinical practice
- In thumb base pain, measure pinch and key grip force and go through daily loading: turning taps and lids is the classic trigger.
- Region in the model
- Upper limb