Manual of Surgery, Alexis Thomson [new books to read txt] 📗
- Author: Alexis Thomson
- Performer: -
Book online «Manual of Surgery, Alexis Thomson [new books to read txt] 📗». Author Alexis Thomson
In the large nerve-trunks of the limbs he has worked out the exact position of the bundles for the various groups of muscles, so that in a cross section of a particular nerve the component bundles can be labelled as confidently and accurately as can be the cortical areas in the brain. In the living subject, by using a fine needle-like electrode and a very weak galvanic current, he has been able to differentiate the nerve bundles for the various groups of muscles. In several cases of spastic paralysis he succeeded in picking out in the nerve-trunk of the affected limb the nerve bundles supplying the spastic muscles, and, by resecting portions of them, in relieving the spasm. In a case of spastic contracture of the pronator muscles of the forearm, for example, an incision is made along the line of the median nerve above the bend of the elbow. At the lateral side of the median nerve, where it lies in contact with the biceps muscle, is situated a well-defined and easily isolated bundle of fibres which supplies the pronator teres, the flexor carpi radialis, and the palmaris longus muscles. On incising the sheath of the nerve this bundle can be readily dissected up and its identity confirmed by stimulating it with a very weak galvanic current. An inch or more of the bundle is then resected.
Injuries of NervesNerves are liable to be cut or torn across, bruised, compressed, stretched, or torn away from their connections with the spinal medulla.
Complete Division of a Mixed Nerve.—Complete division is a common result of accidental wounds, especially above the wrist, where the ulnar, median, and radial nerves are frequently cut across, and in gun-shot injuries.
Changes in Structure and Function.—The mere interruption of the continuity of a nerve results in degeneration of its fibres, the myelin being broken up into droplets and absorbed, while the axis cylinders swell up, disintegrate, and finally disappear. Both the conducting and the insulating elements are thus lost. The degeneration in the central end of the divided nerve is usually limited to the immediate proximity of the lesion, and does not even involve all the nerve fibres. In the distal end, it extends throughout the entire peripheral distribution of the nerve, and appears to be due to the cutting off of the fibres from their trophic nerve cells in the spinal medulla. Immediate suturing of the ends does not affect the degeneration of the distal segment. The peripheral end undergoes complete degeneration in from six weeks to two months.
The physiological effects of complete division are that the muscles supplied by the nerve are immediately paralysed, the area to which it furnishes the sole cutaneous supply becomes insensitive, and the other structures, including tendons, bones, and joints, lose sensation, and begin to atrophy from loss of the trophic influence.
Nerves divided in Amputation.—In the case of nerves divided in an amputation, there is an active, although necessarily abortive, attempt at regeneration, which results in the formation of bulbous swellings at the cut ends of the nerves. When there has been suppuration, and especially if the nerves have been cut so as to be exposed in the wound, these bulbous swellings may attain an abnormal size, and are then known as “amputation” or “stump neuromas” (Fig. 84).
When the nerves in a stump have not been cut sufficiently short, they may become involved in the cicatrix, and it may be necessary, on account of pain, to free them from their adhesions, and to resect enough of the terminal portions to prevent them again becoming adherent. When this is difficult, a portion may be resected from each of the nerve-trunks at a higher level; and if this fails to give relief, a fresh amputation may be performed. When there is agonising pain dependent upon an ascending neuritis, it may be necessary to resect the corresponding posterior nerve roots within the vertebral canal.
Fig. 84.—Stump Neuromas of Sciatic Nerve, excised forty years after the original amputation by Mr. A. G. Miller.
Other Injuries of Nerves.—Contusion of a nerve-trunk is attended with extravasation of blood into the connective-tissue sheaths, and is followed by degeneration of the contused nerve fibres. Function is usually restored, the conducting paths being re-established by the formation of new nerve fibres.
When a nerve is torn across or badly crushed—as, for example, by a fractured bone—the changes are similar to those in a divided nerve, and the ultimate result depends on the amount of separation between the ends and the possibility of the young axis cylinders bridging the gap.
Involvement of Nerves in Scar Tissue.—Pressure or traction may be exerted upon a nerve by contracting scar tissue, or a process of neuritis or perineuritis may be induced.
When terminal filaments are involved in a scar, it is best to dissect out the scar, and along with it the ends of the nerves pressed upon. When a nerve-trunk, such as the sciatic, is involved in cicatricial tissue, the nerve must be exposed and freed from its surroundings (neurolysis), and then stretched so as to tear any adhesions that may be present above or below the part exposed. It may be advisable to displace the liberated nerve from its original position so as to minimise the risk of its incorporation in the scar of the original wound or in that resulting from the operation—for example, the radial nerve may be buried in the substance of the triceps, or it may be surrounded by a segment of vein or portion of fat-bearing fascia.
Injuries of nerves resulting from gun-shot wounds include: (1) those in which the nerve is directly damaged by the bullet, and (2) those in which the nerve-trunk is involved secondarily either by scar tissue in its vicinity or by callus following fracture of an adjacent bone. The primary injuries include contusion, partial or complete division, and perforation of the nerve-trunk. One of the most constant symptoms is the early occurrence of severe neuralgic pain, and this is usually associated with marked hyperæsthesia.
Regeneration.—Process of Repair when the Ends are in Contact.—If the wound is aseptic, and the ends of the divided nerve are sutured or remain in contact, they become united, and the conducting paths are re-established by a regeneration of nerve fibres. There is a difference of opinion as to the method of regeneration. The Wallerian doctrine is that the axis cylinders in the central end grow downwards, and enter the nerve sheaths of the distal portion, and continue growing until they reach the peripheral terminations in muscle and skin, and in course of time acquire a myelin sheath; the cells of the neurolemma multiply and form long chains in both ends of the nerve, and are believed to provide for the nourishment and support of the actively lengthening axis cylinders. Another view is that the formation of new axis cylinders is not confined to the central end, but that it goes on also in the peripheral segment, in which, however, the new axis cylinders do not attain maturity until continuity with the central end has been re-established.
If the wound becomes infected and suppuration occurs, the young nerve fibres are destroyed and efficient regeneration is prevented; the formation of scar tissue also may constitute a permanent obstacle to new nerve fibres bridging the gap.
When the ends are not in contact, reunion of the divided nerve fibres does not take place whether the wound is infected or not. At the proximal end there forms a bulbous swelling, which becomes adherent to the scar tissue. It consists of branching axis cylinders running in all directions, these having failed to reach the distal end because of the extent of the gap. The peripheral end is completely degenerated, and is represented by a fibrous cord, the cut end of which is often slightly swollen or bulbous, and is also incorporated with the scar tissue of the wound.
Clinical Features.—The symptoms resulting from division and non-union of a nerve-trunk necessarily vary with the functions of the affected nerve. The following description refers to a mixed sensori-motor trunk, such as the median or radial (musculo-spiral) nerve.
Sensory Phenomena.—Superficial touch is tested by means of a wisp of cotton wool stroked gently across the skin; the capacity of discriminating two points as separate, by a pair of blunt-pointed compasses; the sensation of pressure, by means of a pencil or other blunt object; of pain, by pricking or scratching with a needle; and of sensibility to heat and cold, by test-tubes containing water at different temperatures. While these tests are being carried out, the patient's eyes are screened off.
After division of a nerve containing sensory fibres, there is an area of absolute cutaneous insensibility to touch (anæsthesia), to pain (analgesia), and to all degrees of temperature—loss of protopathic sensibility; surrounded by an area in which there is loss of sensation to light touch, inability to recognise minor differences of temperature (72°–104° F.), and to appreciate as separate impressions the contact of the two points of a compass—loss of epicritic sensibility (Head and Sherren) (Figs. 91, 92).
Motor Phenomena.—There is immediate and complete loss of voluntary power in the muscles supplied by the divided nerve. The muscles rapidly waste, and within from three to five days, they cease to react to the faradic current. When tested with the galvanic current, it is found that a stronger current must be used to call forth contraction than in a healthy muscle, and the contraction appears first at the closing of the circuit when the anode is used as the testing electrode. The loss of excitability to the interrupted current, and the specific alteration in the type of contraction with the constant current, is known as the reaction of degeneration. After a few weeks all electric excitability is lost. The paralysed muscles undergo fatty degeneration, which attains its maximum three or four months after the division of the nerve. Further changes may take place, and result in the transformation of the muscle into fibrous tissue, which by undergoing shortening may cause deformity known as paralytic contracture.
Vaso-motor Phenomena.—In the majority of cases there is an initial rise in the temperature of the part (2° to 3° F.), with redness and increased vascularity. This is followed by a fall in the local temperature, which may amount to 8° or 10° F., the parts becoming pale and cold. Sometimes the hyperæmia resulting from vaso-motor paralysis is more persistent, and is associated with swelling of the parts from œdema—the so-called angio-neurotic œdema. The vascularity varies with external influences, and in cold weather the parts present a bluish appearance.
Trophic Phenomena.—Owing to the disappearance of the subcutaneous fat, the skin is smooth and thin, and may be abnormally dry. The hair is harsh, dry, and easily shed. The nails become brittle and furrowed, or thick and curved, and the ends of the fingers become club-shaped. Skin eruptions, especially in the form of blisters, occur, or there may be actual ulcers of the skin, especially in winter. In aggravated cases the tips of the fingers disappear from progressive ulceration, and in the sole of the foot a perforating ulcer may develop. Arthropathies are occasionally met with, the joints becoming the seat of a painless effusion or hydrops, which is followed by fibrous thickening of the capsular and other ligaments, and terminates in stiffness and fibrous ankylosis. In this way the fingers are seriously crippled and deformed.
Treatment of Divided Nerves.—The treatment consists in approximating the divided ends of the nerve and placing them under the most favourable conditions
Comments (0)