Hand

The metacarpus

The metacarpus consists of five bones, the metacarpals, one corresponding to each digit and numbered in sequence from the lateral side. Each is a long bone with a proximal quadrilateral base, a shaft and a distal rounded head. The variations in shape of the ases provide a means of distinguishing them. The base of the first metacarpal has a saddle-shaped articular surface which fits a corresponding surface on the trapezium. The base of the second metacarpal articulates with the trapezium, trapezoid and capitate. The base of the third has a single articulation with the capitate. The bases of the fourth and fifth metacarpals articulate with the hamate. The bases of the second to fifth also articulate with the adjacent metacarpal bones, having articular facets in appropriate positions.

The heads of the metacarpals are smooth and rounded, extending further onto the palmar surface. The palmar articular margin is notched in the midline. The head of the first metacarpal is wider than the others having two sesamoid bones, usually found in the short tendons crossing the joint and which articulate with the palmar part of the joint surface occasionally grooving it. The heads fit into a concavity on the base of the proximal phalanx at the metacarpophalangeal joints. The shaft of the metacarpals is slightly curved with a longitudinal palmar concavity. That of the first metacarpal is nearly as wide as the base and has a rounded dorsal surface. The palmar surface is divided by a blunt ridge into a larger lateral part and a smaller medial part.

Palpation

If the fingers are flexed to form a fist, the heads of the metacarpals can easily be palpated as the knuckles. Running proximally on the dorsal surface of the hand the shafts can also be distinguished. At the proximal end of the shaft the gap between the base of the metacarpal and the carpus can be palpated as the line of the carpometacarpal joint.

Ossification

Primary ossification centres appear in the shaft in the ninth week in utero, so that the bones are well ossified at birth. Secondary centres appear in the heads of the second to fifth metacarpals between 2 and 3 years. The secondary centre for the base of the first metacarpal appears slightly later. Fusion of the epiphysis with the shaft occurs between 17 and 19 years for all metacarpals. Occasionally, a secondary centre may appear in the head of the first metacarpal.

The phalanges

There are 14 phalanges in each hand, three for each finger and two for the thumb. As they are long bones, each phalanx has a shaft, a large proximal end and a smaller distal end, the head. The phalanges of the thumb are shorter and broader than those of the fingers.

The proximal phalanx has a concave oval facet on its base for articulation with the head of the metacarpal. The rounded head, which extends further onto the palmar surface, has a wide, pulley – shaped articular surface for the base of the next phalanx. The shaft is curved along its length being convex dorsally. It is convex from side to side on its dorsal surface, and is flat on the palmar surface. The middle and distal phalanges are similar to the proximal phalanx. However, the base of the distal phalanx is large, and the head is expanded to support the pulp pad of the digits.

By convention, the digits are described by name rather than by number, and are from lateral to medial, the thumb, index, middle, ring and little fingers.

Palpation

By flexing the fingers into a fist, the heads of the proximal and middle phalanges can be palpated. The shafts of the phalanges are also easily followed throughout their length, especially on their dorsal surface.

Ossification

Primary ossification centres appear in the shafts of the phalanges between the eighth and twelfth week in utero, with the distal phalanges ossifying first. Secondary centres appear in the bases of the phalanges during the second and third year, fusing with the shaft between 17 and 19 years. Occasionally, a secondary centre may appear in the head as well as in the base.