The tubercle of the trapezium is a vertical ridge on the palm side of the trapezium, at the base of the thumb. With the scaphoid tubercle it anchors the outer end of the flexor retinaculum, forming the lateral wall of the carpal tunnel, and the flexor carpi radialis tendon runs in a groove just on its medial side. Several thenar muscles take origin from it.
| Articulations |
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|---|---|
| Landmarks |
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| Ossification | The trapezium ossifies from a single centre that appears at about 4-6 years of age. |
Fractures of the trapezial ridge are uncommon and easily missed on standard wrist X-rays; a carpal tunnel view or CT shows them. Tenderness just distal to this point, made worse by grinding the thumb metacarpal against the trapezium, points to thumb base osteoarthritis. The ridge is a reference point in carpal tunnel release.
Turn the hand palm up and extend the wrist slightly. Find the scaphoid tubercle at the distal wrist crease at the base of the thenar eminence, then move about 1 cm further toward the thumb and fingers. Press firmly through the thenar muscles to feel a deep bony ridge; gently moving the thumb metacarpal helps confirm you are on the trapezium.
A fall on the outstretched hand or direct blow to the thenar area breaks the ridge, causing pain with gripping and pinching.
Wear of the joint between the trapezium and the first metacarpal, causing aching at the base of the thumb and weak pinch, very common in older women.
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