Tubercle of trapezium bone

The tubercle of the trapezium (tuberculum ossis trapezii) is a palpable bony ridge/prominence on the palmar (volar) surface of the trapezium, the most radial bone of the distal carpal row. In standard anatomical usage this "tubercle" refers to the trapezial ridge (crest of the trapezium), an oblique elevation on the anterior/palmar aspect of the bone that serves as an attachment point for the flexor retinaculum (transverse carpal ligament) and forms the radial (lateral) boundary of the carpal tunnel, together with the tubercle of the scaphoid. Medial to this ridge lies a vertical groove that transmits the tendon of the flexor carpi radialis as it courses toward its insertion.

Location and relations: The ridge/tubercle projects palmarly and forms the lateral wall of the carpal tunnel; the median nerve and flexor carpi radialis tendon run in close proximity, which is why fractures or non-union here can cause median nerve or FCR tendon irritation.

Ligamentous attachment: It anchors the flexor retinaculum (transverse carpal ligament). Avulsion of this ligament, or direct trauma from a fall onto an outstretched hand, produces the uncommon trapezial ridge fracture, classified as type I (fracture at the base of the ridge) or type II (fracture at the tip).

Other named tubercles: The trapezium also has smaller dorsal tubercles described in the literature — a dorsoradial tubercle (site of attachment of the dorsoradial ligament and the first dorsal interosseous aponeurosis, contributing to trapeziometacarpal joint stability) and a dorsoulnar tubercle (which can undergo isolated, easily missed fractures). The palmar "trapezial ridge/tubercle" and these dorsal tubercles are distinct structures, so the intended meaning depends on context.