Amputation (Lat. amputare, to cut off), a surgical operation by which a limb or portion of a limb, or a naturally projecting part of the body, is removed. The cutting away of a tumor is spoken of as an extirpation or excision. Amputation is required where the part is injured or diseased to such an extent as to render it useless and inconvenient, or a source of danger to life if it be retained. For many centuries an operation of extreme danger in itself, and performed only in the most urgent cases, surgical advance has rendered it one of little risk, though of late years there has been a tendency to curtail its sphere by improvements in other departments of the science. It was at first performed by a division of all the parts at the same level, and only through a joint. About the 1st century the practice of amputating between the joints was introduced, and also the very important principle of dividing the bone at a higher level than the soft parts, that the cut surfaces of these latter may be joined together over the bone and unite in that position.

Formerly the great source of danger was the haemorrhage which took place during and after the operation; to prevent which the parts were divided with red-hot knives, or the cut surfaces treated with heated irons or boiling liquids, in order to produce a charring of the tissues and plugging of the mouths of the vessels. A band encircling the limb, to restrain the bleeding during the operation, was used as early as the 1st century, but its permanent arrest was for a long time effected only by the means already mentioned. The band, applied ignorantly, failed of its complete purpose, and the inevitable separation of the eschars produced by hot bodies in many cases opened afresh the vessels, and haemorrhage and death were the result. The use of the ligature in amputation, especially as its proper application was developed, rendered the operation comparatively safe. The honor of its introduction is probably due to Ambroise Pare in the 16th century. If the ligature was employed in these cases by Celsus, it fell into immediate disuse; and even the teachings of Pare and his school were unable for many years to bring it into general favor. The invention of the tourniquet by Morel and its perfection by Petit, in the 17th and 18th centuries, still further diminished the dangers.

When it is done for a disease, it is spoken of as a pathological amputation; when for an injury, it is named "primary" or "secondary," according as it is performed before or after the occurrence of the inflammation which is induced by the violence done to the part. During the inflammatory period the operation is contra-indicated except for some very urgent reason. The deaths following primary amputations are somewhat fewer in number than those after secondary, except in the case of the thigh. Where done for disease, the mortality is very much less. No rule in surgery is better established than that the death rate increases as we approach the trunk. An amputation of the leg is less dangerous than of the thigh, and that through the lower part of the thigh less than through its upper part. Moreover, an amputation through the upper extremity is less grave than one through a corresponding part of the lower extremity. - In performing amputation, the patient is placed under the influence of an anaesthetic, which by its abolition of pain and much of the terror diminishes the shock to his system, and enables the surgeon to operate more carefully and on a part deprived of motion. The circulation through the main artery is arrested by pressure with the finger or the tourniquet.

The skin and muscles are then cut by a series of sweeps of the knife round the circumference of the limb, the parts being drawn toward the trunk by an assistant as each one is completed. In this way, as the bone is approached, the parts are divided at a higher and higher level. The bone is then sawed, the sharp edges or corners being rounded off so as not to press upon the part. The chief arteries are treated in such a way as to close their open extremities. This may be done by grasping the end with the forceps and twisting it several times, which is called torsion; or by pressure with a needle passed through the muscles and over or through the vessel, called acupressure; or, most usually, by tying it with a ligature, which consists of a well waxed string of silk or other material. The tourniquet is then removed, and the small vessels which bleed are treated in the same way, provided the contact with the air does not cause them to contract. The soft parts are then drawn over the end of the bone and stitched together. The method of cutting the soft parts described above is known as the circular. What is called the flap operation may be performed by transfixion, cutting from within outward, or by cutting from without inward. In either case a single or a double flap may be made.

This latter process may be rendered intelligible by taking a circular piece of paper and folding it along one of its diameters. The centre of the circle would represent the situation of the end of the bone, and the circumference the margins of the skin which are stitched together.

If the cut surfaces grow together at once, there is said to be primary union. This result is but seldom attained, at least throughout, and as a rule the union is secondary, in which case suppuration takes place, and granulations spring up which grow together and fill up the wound. - For the accidents which may occur after amputation, see Gangrene, HAemorrhage, Necrosis, Osteo-myelitis, and Tetanus.