This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
When it is possible to do so the interarticular fibrocartilage over the lower end of the ulna is not to be interfered with. The lower radio-ulnar joint is therefore not injured and the movements of pronation and supination are preserved.
The styloid process of the radius is 1 cm. below that of the ulna. It is directly on the outer side of the radius, while the styloid process of the ulna is toward the posterior surface.
On account of retraction, the knife is entered 1 cm. (2/5 in.) below the radial styloid process - the thumb being abducted to render the tissues tense, and, if the left hand is being operated on, the knife is carried straight down well on the thenar prominence. It is then curved abruptly across the palm on a level almost or quite as low as the web of the thumb. It is continued to the ulnar side and up to within 1 cm. of the styloid process of the ulna. The flap should be an almost square one with rounded ends. The incision goes down to but does not divide the flexor tendons (Fig. 359).
This flap, embracing the palmar fascia and part of the thenar and hypothenar muscles, is at once raised from the flexor tendons, care being taken not to catch the knife on the unciform and pisiform bones.
The hand is now pronated and a dorsal flap 2.5 cm. (1 in.) long is cut. As the skin is loose and elastic this length is needed to provide against retraction.
The flaps being reflected and the hand flexed, disarticulation is begun by entering the knife on the ulnar side of the dorsum, beneath the styloid process. The joint is followed around to the radial side, bearing in mind that it curves markedly upwards.
If the right hand is being operated on and the knife is entered transversely it will strike the scaphoid bone, therefore it must be at once inclined obliquely upward. Section of the flexor muscles and anterior ligament completes the disarticulation. The radial artery will be cut in the snuff-box. The ulnar will be seen on the inner side of the palmar flap, and on the outer side may be seen the superficial volar. Some small branches of the anterior and posterior carpal and interosseous arteries may require ligation.
Some operators remove the styloid processes of the radius and ulna. If this is done, care is to be taken not to go so high as to injure the insertion of the brachio-radialis on the radius and the attachment of the triangular cartilage on the ulna. Usually the styloid processes are not interfered with, in order to avoid impairing the movements of pronation and supination.
The radial artery can be ligated in the anatomical snuff-box as it crosses the back of the hand to dip between the first and second metacarpal bones and the two heads of the abductor indicis muscle. The course of the artery is indicated by a line drawn from the tip of the styloid process of the radius to the upper end of the first interosseous space (see Fig. 348, p. 338).
Fig. 359 - Amputation through the wrist-joint of the right side.
The incision is usually made in the direction of the tendons from the styloid process down. As soon as the skin is divided there may be exposed in the superficial fascia some branches of the radial nerve and the radial vein. These being pushed aside, the deep fascia is opened and the artery found with its two companion veins lying deep down on the external lateral ligament and trapezium. The most common error in this operation is mistaking the superficial vein for the artery and not searching deep enough.
If the radial artery is wounded as it passes through the snuff-box bleeding will be very free. It is almost impossible to ligate the divided ends in the wound because the proximal end retracts under the short extensor tendons of the thumb and the distal end retracts through the first interosseous space deep into the palm of the hand so that they cannot be reached. When such is the case it is necessary either to ligate the ulnar and radial arteries on the anterior surface just above the wrist or, as we did in one case, pack the wound with antiseptic gauze and keep the hand well elevated.