Fig. 72.—Bones of the right forearm
in a position of supination. (Toldt.)
In the living the olecranon process of the ulna is always felt at the elbow and the posterior border of the ulna forms the prominent ridge down the forearm, leading to the styloid process. The head of the radius is felt just below the external condyle and often makes a dimple in the muscles of the forearm. The rest of its upper half is concealed with muscles, but the lower half is easily felt as there are only tendons over it. The styloid process is felt externally. Normally that of the radius is a little lower than that of the ulna, so that in cases of fracture their relative position is of considerable importance as showing the amount of deformity.
The two forearm bones are more frequently broken together than separately and generally by direct violence, the lower fragment being usually drawn up by the action of the flexor and extensor muscles and producing a swelling on the palmar surface of the forearm. Indirect violence usually causes fracture of the radius only. In both cases, but especially in fracture of both bones, there is a tendency for membrane to get between the fragments, so the arm is put up in splints with the hand midway between pronation and supination in order to separate the bones as far as possible. Care must be taken not to have the bandage too tight or gangrene of the fingers may result. In most fractures of the arm it is put up bent, but in fracture of the olecranon it is put up fully extended, as the fragment is sure otherwise to be displaced by the pull of the triceps. In fact, the olecranon is sometimes fractured by the muscular force of the triceps, though usually its fracture, which is frequent, is due to direct violence. The ulna is also often fractured in the middle by direct violence or the styloid process may be broken. Fracture of the neck or shaft of the radius is very common, the most important arm fracture being that of the lower end of the radius or Colles’ fracture. This and the corresponding fracture in the leg, Pott’s fracture, are two of the commonest fractures. In dislocation of the wrist the normal relation of the two styloid processes remains unchanged, but in Colles’ fracture the lower fragment often projects on the back of the hand, making a typical deformity called the silver fork deformity.
The bones of the wrist and hand had best be described before the forearm muscles are taken up, as the muscles of the forearm are distributed largely to the fingers.
The Wrist.—The wrist or [carpus] is made up of eight bones arranged in two rows of four each. In the first row are the [scaphoid and semilunar bones], on the outer side, articulating with the radius, the [cuneiform] articulating with the fibro-cartilage of the wrist-joint, and the [pisiform]. In the second row, in corresponding positions, are the [trapezium, trapezoid, os magnum], and unciform. The eminence felt on the radial side of the wrist is the protuberance of the scaphoid, while the pisiform is generally felt on the ulnar side.
Fig. 73.—Right carpal bones, dorsal surface. T, trapezium; T´, trapezoid; 7, os magnum; U, unciform; S, scaphoid; L, semilunar; C, cuneiform; P, pisiform.
The Hand.—The hand contains nineteen bones, five metacarpal bones, one for each finger and the thumb, whose bases articulate with the lower row of wrist bones, and fourteen phalanges, three for each finger and two for the thumb, of which the first row articulate with the metacarpal bones. They are all long bones and are slightly concave anteriorly. When the hand is flexed it is the heads of the metacarpal bones, not the bases of the phalanges, that are so prominent, the head of the third metacarpal being most prominent.
The metacarpals are seldom fractured, though bad fractures occasionally occur. In comminuted fracture nothing can be done but remove the bone. If the periosteum is left the bone will grow again. Two diseases sometimes affect the metacarpals and the phalanges, tuberculosis and syphilis. Both cause swelling of the bones.