Human Anatomy Vol 1

UPPER LIMB

Hamate

Trapezium

The year of appearance of centre of ossification in

the carpal bones is shown in Figs 2.35a and b.

Appearance-3rd year

Fusion-18th year

Appearance-2nd year

Fusion-1Bth year

Each bone has a head placed distally, a shaft and a

base at the proximal end.

i. The head is round. It has an articular surface

which extends more anteroposteriorly than

laterally. It extends more on the palmar surface

than on the dorsal surface. The heads of the

metacarpal bones form the knuckles.

ii. The shaft is concave on the palmar surface. Its

dorsal surface bears a flat triangular area in its

distal part.

iii. The base is irregularly expanded.

A metacarpal bone can be distinguished from a

metatarsal bone because of the differences given in

Table 2.3.

Trapezoid

c Frnclure of the scaphoid is qulle corunon. The bone

fractures through the waist at right angles to its

long axis. The fracture is caused by a fall on the

optstretched hand, or on the tips of the fingers.

Tlr.is causes tenderness and swelling in the

anatomical snuff bo>r, and pain on longitudinal

percussion of the thumb and index finger, The

residual disability is more marked in the

midcarpal joint than in the wrist joint. The

importance of the fracture lies in its liability to

nonunionr and avascular necrosis of the body of

thebone. Normally, the scaphoidhas two nutrient

arteries, one entering the palmar surface of the

tubercle and the other the dorsal surface of the

body. Occasionally (13% of cases) both vessels

enter through the tubercle or through the distal

half of the bone. In such cases, fracture may

deprive the proxirnal half of the bone of its blood

supply leading to avascular necrosis (Fig. 2.36).

o Dislocation of the lunate may be produced by a

fall on the acutely dorsiflexed hand with the elbow

joint flexed. This displaces the lunate anteriorly,

also leading to carpaltunnel syndrome like features

(Figs 2.37a to c).

. During scaphoid fracture, pain is felt in the
anatomical snuff box.

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1 The metacarpal bones are 5 miniature long bones,

which are numbered from lateral to the medial side

(Fig.2sa).

Nutrient arteries

Two types of arterial supply

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Necrosis of proximal

segment

Fig. 2.36: Fracture of the scaphoid