Osteology: Metacarpals

The five metacarpal bones make up the palm of the hand. The metacarpals are often referred to by the abbreviation “MC” plus the number of the ray to which they belong. Thus, MC1 is the first metacarpal or the thumb metacarpal. Each metacarpal is a tubular bone, with an expanded base which articulates with one or more carpal bones, and a rounded head which articulates with a manual phalanx. It is much easier to identify and side metacarpals using their bases than their heads.

See the carpals or manual phalanges for more specimens of the hand, wrist, and fingers. Other specimens of may be found in the Digital Teaching Collection.

Metacarpal 1

Metacarpal 2

Metacarpal 3

Metacarpal 4

Metacarpal 5

The first metacarpal is easily recognizable. It is the shortest and broadest of the metacarpals. Its base has large saddle-shaped articulation for the corresponding facet on the trapezium. MC1 is the only metacarpal which does not articulate with another metacarpal. The head of MC1 is considerably flatter than the more rounded heads of the other metacarpals.

Siding: MC1 can be sided using the asymmetrical nature of the saddle-shaped base. The lateral portion of the saddle is more elongate and narrower than the medial portion.

The second metacarpal is usually the longest of the metacarpals. The dorsal aspect of the base is distinctively W shaped. There are three articular surfaces visible in proximal view. The trapezoid facet is located in between a smaller facet for the trapezium on the lateral side of the bone and a blunted projection on the medial side which ends in a small facet for the capitate. The medial side of this blunted projection bears the proximal-distally oriented facet for MC3. MC2 does not articulate with MC1.

Siding: MC2 can be sided because the blunted, proximal-most projection of the base is medial.

The third metacarpal is distinguished by its styloid process which projects proximally from the dorsal-lateral corner of the base. The broad articular surface on the proximal end is for the capitate. The medial and lateral sides bear articulations for MC4 and MC2 respectively. These facets are usually double, with two small separate articular surfaces oriented in the same plane.

Siding: The position of the styloid process on the dorsal and lateral side of the base makes siding relatively straightforward

The fourth metacarpal has an almost square base in proximal view. The large proximal articular surface is for the hamate. The medial side of the base has a small facet for MC5 which meets the facet for the hamate at a 90° angle. The lateral facet for MC3 is usually a double facet.

Siding: The most useful feature for siding MC4 is the pronounced 90° angle formed by the articular surfaces for the hamate and MC5 on the medial side of the base.

The fifth metacarpal is easy to recognize because it is quite small and its base bears only a single metacarpal articulation, in addition to the proximal articulation for the hamate. The lateral margin of the base bears an articular facet for MC4. It lacks any metacarpal articular facet on the medial margin of the base. The medial side of the base bears a medial tubercle in the same position that other metacarpals have metacarpal articulations.

Siding: The medial location of the medial tubercle makes siding straightforward.