Upper limb
Trapezoid bone
Os trapezoideum
- Origin
- Smallest bone of the distal row, wedge shaped with the broad side facing backwards. Wedged between the trapezium, the capitate, the scaphoid and the base of the second metacarpal.
- Insertion
- Attachment for the trapeziotrapezoid and trapezoidocapitate ligaments and for part of flexor pollicis brevis.
- Function
- Anchors the second ray and so forms, with the capitate, the fixed central pillar around which the hand folds.
- Innervation
- Posterior interosseous nerve (articular branches, C6-C7)
- Movement & chain
- Practically immobile: the carpometacarpal joint of the index finger allows only a few degrees, and that is exactly the point.
- Palpation
- From the back, in line with the second metacarpal and distal to Lister tubercle; it lies deeper than its neighbours.
- Clinical
- Rarely affected thanks to its sheltered position and strong ligaments. An isolated fracture or dislocation points to high energy trauma and almost always comes with injury to its neighbours.
- Segmental innervation
- C6-C7
- In clinical practice
- In dorsal wrist pain after a fall, do not stop at the scaphoid: the whole distal row deserves a systematic check.
- Region in the model
- Upper limb