First metacarpal bone: Difference between revisions

Revision as of 07:57, 3 December 2017

Revision as of 08:03, 3 December 2017

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The body or shaft is thick and broad — averaging {{convert|6|to|11|mm}}. On its dorsal side, the shaft is flat and wide, while the anteroposterior side is less pronounced; usually resulting in an oval-triangular cross-section.

The dorsal surface of the shaft is weakly convex longitudinally, while its palmar, radial, and ulnar surfaces tend to be concave. The palmar and medial surface exhibits a blunt ridge which separates a larger lateral part – the insertion of the [[opponens pollicis muscle]] – and a smaller medial part – the origin of the lateral head of the first [[Dorsal interossei of the hand|dorsal interosseous muscle]].

<ref name="Doyle-Shaft">{{harvnb|Doyle|Botte|2003| loc=Shaft of the Thumb Metacarpal}}</ref><!-- ref for subsection -->

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The base is significantly different from the bases of the other metacarpals. It is trumpet-shaped and ends in a saddle-shaped articular surface matching that of the trapezial articular surface. The configuration of the thumb carpometacarpal joint plays an important role in the mechanism of opposition. The articular surface is delimited by a thick, crest-like ridge extending around its circumference.

On the palmar (and lateral) side of the base is the insertion of the tendon of the [[abductor pollicis longus muscle]], usually featuring a small tubercle. The origin of the first [[Palmar interossei muscles|palmar interosseous muscle]] is on the ulnar aspect of the base, and can sometimes extend onto the shaft. In contrast to the other metacarpals, the first metacarpal has no articular facets on the sides of its base (for intermetacarpal articulations) because it articulates exclusively with the trapezium.

<ref name="Doyle-Base">{{harvnb|Doyle|Botte|2003| loc=Base of the Thumb Metacarpal}}</ref><!-- ref for subsection -->